LECTURE NOTES ON SPINAL ANATOMY (AN 1330) BY Dr. ISIS ZAKI M.D., M.S., Ph.D. TEXAS CHIROPRACTIC COLLEGE BASIC SCIENCE DEPARTMENT VERTEBRAL COLUMN Introduction and overview: - AKA; spinal column (backbone, spine). - Extends from the skull to the tip of the coccyx. - Forms the main part of the axial skeleton (skull, vertebral column, ribs, sternum and hyoid bone). - Formed of alternating bony vertebrae & fibrocartilagenous intervertebral discs (IVDs). - The vertebrae are connected by strong ligaments, supported and moved by powerful musculotendinous masses. Number of vertebrae: - The vertebral column is formed of 33 vertebrae in new born (7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal). - In the adult, it is formed of 24 true movable vertebrae (7 cervical, 12 thoracic, 5 lumbar) and 2 false (composite) vertebrae: 1 sacrum and 1 coccyx (Total= 26). Length: - 71 cm in male (28?): Cervical: 12.5 cm Thoracic: 28 cm Lumbar: 18 cm Sacral and coccygeal: 12.5 cm 61 cm in females (25?) In the morning, the vertebral column is 2 cm longer due to imbibition of water by IVDs (nucleus pulposus) at night. Intervertebral Discs (IVDs): - There are 23 IVDs that contribute to 25% of the total length of the vertebral column. - There are no IVDs between the occiput-C1, C1-C2. The first IVD is between C2-C3. - They are thickest in the lumbar region and smallest in the cervical region. Pyramids: - When the vertebral column is viewed from the front, there are 2 major pyramids that could be observed using the transverse diameter of vertebral bodies as a reference: Long upright pyramid: extends between the axis (C2) to fifth lumbar (L5). Short inverted pyramid: base of sacrum to tip of coccyx. - The long general upright pyramid may be subdivided into 3 smaller pyramids: An upright pyramid: Apex at odontoid process of C2 and base at body of T1 vertebra. An inverted pyramid: Base at body of T1 vertebra and apex at T5 vertebra. An upright pyramid: Apex at T5 and base at L5. Curves of the spine: The lateral view of the vertebral column displays 4 curves of 2 types: I. Primary/Kyphotic curves (present at birth and develop during fetal life): Thoracic. Sacral. - They are concave anteriorly - They are due to difference in height between the anterior and posterior parts of vertebral bodies. - They are accommodation curves to accommodate for thoracic, abdominal and pelvic viscera. II. Secondary/Lordotic curves (appear after birth): 3. Cervical: forms at 3-4 months (baby holds his head erect). 4. Lumbar: forms at 12-18 months (walking) - They are convex anteriorly. - They are due to difference in thickness between anterior and posterior parts of IVDs. - They are compensation curves since they compensate for a change in posture; holding the head erect and walking. The curves of the spine increase its resistance to axial compression. It can withstand up to 700 Ibs of axial pressure. Abnormal curvatures of vertebral column: (1) Kyphosis (humpback, hunchback): Abnormal increase in the thoracic curvature (anterior concavity). Could be due to osteoporosis. (2) Lordosis (swayback, hollow back): Abnormal increase in lumbar curvature (anterior convexity). Pregnant women develop lordosis to compensate for change in their line of gravity during late months of pregnancy. Obesity( lordosis and low back pain (potbelly). (3) Scoliosis (croaked or curved back): - Abnormal lateral curvature of the spine (right or left) accompanied by rotation of vertebrae. The spinous processes point towards the concavity. It may be structural (developmental) or functional (mechanical or neurological). Functions of vertebral column: (1) Protects the spinal cord and spinal nerves. (2) Supports the weight of the body. (3) Provides a rigid and flexible axis for the body and pivot for the head. (4) Plays an important role in posture and locomotion. (5) Resiliency: has the ability to absorb shock that may damage visceral structures. STRUCTURE AND FUNCTION OF VERTEBRAE TYPICAL VERTEBRAE - Possess the following parts: A vertebral body and a vertebral arch formed of: 2 pedicles 2 laminae One spinous process 2 transverse processes 4 articular processes (2 superior, 2 inferior) The vertebra is formed of an outer layer of compact bone and a core of trabecular (spongy) bone that contains the red bone marrow. The pattern of trabeculation is variable as it develops along the lines of greatest stress. - The vertebra is an irregular bone covered by periosteum that is innervated by nerve fibers that transmit pain and proprioception. - The density of the bone increases during puberty, reaches a peak during midtwenties and then decreases gradually, with marked decrease at menopause. A decrease in bone density = osteoporosis. - Osteoporosis may predispose to vertebral fractures (because of the weight-bearing function of the spine). Vertebral body (centrum): - It is the anterior, largest part of the vertebra. - It increases in size from above downward( weight bearing. - The bodies of successive vertebrae are connected to one another by IVDs. - The bodies are concave posteriorly and form the anterior part of vertebral foramina. - The upper and lower surfaces of the body are covered by hyaline cartilage: cartilaginous end plate (CEP)/ vertebral end plate. - The anterior surface shows foramina for nutrient arteries. - The posterior surface has one or two foramina for exit of basivertebral veins. Vertebral arch (neural arch): - It is posterior to the vertebral body and is formed of 2 pedicles and 2 laminae. - The vertebral arch and the posterior surface of vertebral body form the vertebral foramen. The succession of vertebral foramina in the articulated column forms the vertebral canal (spinal canal), which contains the spinal cord, meninges, fat, nerve roots of spinal nerves and blood vessels. - The vertebral arch protects the spinal cord and associated structures. - Vertebral foramina are trefoil in shape in cervical, lumbar and sacral regions of spinal column and circular and smallest in thoracic region - The antero-posterior diameter of vertebral canal/neural canal is 15 mm in lumbar region, less than that is considered spinal stenosis Pedicles (roots): - Short strong processes that project backwards from the upper portion of vertebral body. - Pedicles form the anterior part of the vertebral arch. - Each pedicle possesses a shallow superior and a deep inferior vertebral notch. - The superior and inferior vertebral notches of adjacent vertebrae contribute to the formation of IVF(contains spinal nerve roots, vessels and dorsal root ganglia). - A loss of proper vertebral relationship may alter the IVFs in such a manner as to create insult to the structures found there. - The size of IVFs (31 pairs) decrease with age. A smaller IVF size was found among patients with chronic neck pain. Laminae: - They are continuous with the pedicles. - Flat, broad plates of bone that form the posterior part of the vertebral arch. They curve posteromedially to meet the middle line at the spinous process. - Seven processes arise from the vertebral arch of a typical vertebra: A spinous process: Projects posteriorly from the vertebral arch at the junction of the laminae. Spinous processes serve as levers for muscle attachments (extension, lateral flexion and rotation). Two transverse processes (TPs): Project laterally from the junction of the pedicles and laminae They serve as muscle attachment sites where rotation and lateral flexion of the spine can occur. Each TP is composed of the true TP (posteriorly) and a costal element (anteriorly): The cervical costal elements( anterior tubercles. The thoracic costal element ( develop into ribs. The lumbar costal elements( anterior aspects of TPs. The sacral costal elements( alae of sacrum (right and left). Four articular processes (Greek: zygapophyses): - 2 superior (pre-zygapophyses) and 2 inferior (post-zygapophyses). - Arise from the junctions of the pedicles and laminae (pediculolaminar junction). - The articular processes are oriented in different planes in different regions of the vertebral column and this affects the type and range of motion in each region.The joint between inferior articular process of one vertebra and the superior articular process of the vertebra below forms zygapophyseal joint (Z/ facet joint). - Function of articular processes: restrict movements in certain directions and to prevent vertebrae from slipping anteriorly. - Thus, each motion segment (functional spinal unit)) of the vertebral column is formed of 2 vertebrae and 3 joints: IVD (anteriorly) and 2 facet joints (posteriorly). - Clinical consideration: Pain from IVDs and facet joints is a common cause of back pain, which could be treated by spinal adjustment. ATYPICAL VERTEBRAE They either lack a necessary descriptive part or possess a peculiar feature. They are: Cervical: C1, 2 and 7. Thoracic: T1, 9, 10, 11 and 12. Lumbar: L5 Sacrum and coccyx. REGIONAL CHARACTERISTICS OF VERTEBRAE Cervical vertebrae - Form the bony skeleton of the neck (cervix = neck). - Located between the skull and thorax. - The smallest of the 24 movable vertebrae because they bear less weight than the subsequent vertebrae. - All cervical vertebrae are characterized by having foramina in the TPs/transverse foramina (for passage of vertebral arteries and veins except those of the C7 which transmit only vertebral veins). - The vertebral foramina are triangular/trefoil and large to accommodate the cervical enlargement of the spinal cord. TYPICAL CERVICAL VERTEBRAE: - C3 ? C6. - The vertebral bodies are small, rectangular when viewed from above. Their transverse diameter increases from C2-C7. - The anterior surface of the vertebral body is convex, the posterior surface is flat. - Two lateral lips (uncinate processes) project upwards from the superior surface of each typical vertebra. One anterior inferior lip projects down from vertebral body. - Uncovertebral joints (of Luschka) form at the uncinate processes of successive vertebrae( interlocking of cervical vertebrae. - The uncinate processes allow for flexion and extension and limit lateral flexion in cervical spine. - The TPs of typical cervical vertebrae show anterior and posterior tubercles. The large anterior tubercles of C6 are called carotid tubercles because the common carotid arteries may be compressed against them to control bleeding from these vessels. - The spinous processes are short and bifid (SPs develop from two separate centers of ossification). - The superior articular facets face mainly posterosuperiorly and the inferior articular facets face mainly anteroinferiorly. They are oriented in a plane that makes 45o with the horizontal. This orientation determines the motion. ATYPICAL CERVICAL VERTEBRAE: ATLAS (C1): A ring of bone - It is given its name because it supports the weight of the head (Atlas: Greek= God). - Has no body. - Has no spinous process. - Has two arches, 2 lateral masses (forming atlas ring) and 2 TPs. - Anterior arch: - is smaller than the posterior arch (1/5 of the atlas ring). - has a tubercle on its anterior surface (longus colli muscle and ALL ligament). - has a smooth articular facet (fovea dentalis) on its posterior surface for articulation with the dens (odontoid process of axis; C2). - can easily pivot (rotate) around the dens at this joint. - Posterior arch: - is larger, forms about 2/5 of the ring of the atlas. - has a posterior tubercle for attachment of ligamentum nuchae and origin of rectus capitis posterior minor. - superior surface has a groove for vertebral artery (sulcus arteriae vertebralis) and suboccipital nerve (C1). - Lateral masses: - Each lateral mass forms 1/5 of the atlas ring. - Consist of a superior articular process and an inferior articular process. - The superior articular facets are concave, narrow in the center (kidney-shaped) and articulate with the occipital condyles to form the atlanto-occipital joint. - The inferior articular facets are flat or slightly concave and articulate with the superior articular facets of C2 to form the lateral atlantoaxial joints. - The medial surface of each lateral mass has a small tubercle for attachment of the transverse ligament of the atlas. - Transverse processes: The TPs of the atlas are large and strong and thus the atlas is wider than all other cervical vertebrae, except for C7 occasionally. They have transverse foramina for the passage of vertebral arteries and veins. TPs serve as sites of muscle attachments. TPs of the atlas don?t have anterior or posterior tubercles as typical cervicals - Vertebral foramen (neural ring): - Large, triangular (trefoil) - Anterior one-third is filled with odontoid process. - Middle one-third is filled with spinal cord. - Posterior one-third: epidural fat and blood vessels. AXIS (C2): - Second cervical vertebra (AKA: epistropheus = pivot) - The strongest, thickest of cervical vertebrae. - It is the main site of rotation of the head (pivot). - It is formed of the following parts: (1) Vertebral body: - Presents a lip anteroinferiorly that overlaps third cervical vertebra. - Its anterior surface presents a midline ridge and 2 shallow grooves on each side. - Its lower surface articulates with the third cervical vertebra at the first IVD. (2) Dens (odontoid process): - A blunt tooth-like process that projects upwards from the body. It is believed to be the body of the atlas that fused with the axis during development. - It articulates anteriorly with the atlas at the fovea dentalis. - It is held in position by the transverse ligament of the atlas posteriorly (ADI: Atlas Dens Interval, is also known as predental space or atlanto-odontoid interspace; AOI). - Clinical consideration: i. Fracture of the dens( posterior displacement( injury of the spinal cord( quadriplegia or injury of medulla oblongata( death. ii. Fracture of the pedicles (Hangman?s fracture) ( death or quadriplegia. iii. Os Odontoideum: unfused odontoid ; shows on X-ray What are the normal measurements of ADI? What could be the cause of increased ADI? (3) Pedicles: - They are thick and strong. - The inferior vertebral notch is deep. - Superior articular processes: lie flush with the pedicles (do not project superiorly). (4) Laminae: - They are taller, thicker and stronger than the rest of cervical vertebrae. - They fuse posteriorly to form spinous process. (5) TPs: are the smallest of cervical vertebrae. (6) Spinous processes: - Bifid, broad, large and very strong. - Palpated 5 cm below the EOP. VERTEBRA PROMINENS (C7): - C7 is so called because of its prominent spinous process (longest and most easily palpated cervical spine). - Spinous process is not bifid. - Serves for muscle attachments. - Transverse processes: are unique: The anterior tubercle is small. The posterior tubercle is large. The anterior tubercle is the costal element of C7 and may develop into a cervical rib. The transverse foramen is small. Why? OCCIPUT (CO) - The external surface of the occipital bone is so intimately related to the cervical spine (direct articulation, muscle and ligamentous attachment). - Occiput is pierced by the foramen magnum which divides it into 3 parts: (1) Squamous (2) Lateral (condylar): right and left (3) Basilar - Squamous part: - Located posterior to foramen magnum. - External occipital protuberance (EOP): most prominent part. - Its center (summit) is known as inion (provides attachment for a muscle and a ligament). - External occipital crest (EOC): extends inferiorly from EOP. - Superior nuchal lines: extend laterally from EOP (attachment of trapezius and SCM muscles) - Inferior nuchal lines: extend laterally and inferiorly from EOC. - Highest (supreme) nuchal lines: extend laterally and superiorly from EOP, are not always prominent. - Condylar parts: - Located lateral to the foramen magnum. - Include: occipital condyles, jugular notch and jugular process. - Occipital condyles are convex, located on each side of the foramen magnum and articulate on each side with the superior articular facets of the atlas. - On the medial surface of each condyle is a tubercle for attachment of the alar ligament. - The jugular notch is a groove along the lateral margin of each side of the occiput. It forms the jugular foramen with the temporal bone. - The jugular process projects laterally from the jugular notch. The rectus capitis lateralis (laterally flexes the head) is attached to it. - Basilar part: - Located anterior to the foramen magnum, it meets the back of body of sphenoid bone to form the clivus that accommodates the brain stem. - The superior constrictor muscle of the pharynx is attached to pharyngeal tubercle (on its outer aspect). - Many ligaments are attached to the basilar part of occipital bone e.g. apical ligament, alar ligaments, superior band of cruciform ligament, and tectorial membrane. OVERVIEW AND CLASSIFICATION OF JOINTS - Joints hold bones together and may or may not permit some degree of movements. - Articulation is the area of contact between bones. Structural classification: Joints can be classified according to the presence or absence of a space between the articulating surfaces (joint cavity) and the type of connective tissue that binds the bones together into 3 types: 1. Fibrous joints: no joint cavity, held together by fibrous connective tissue. 2. Cartilagenous joints: no joint cavity, held together by cartilage. 3. Synovial joints: joint cavity, synovial membrane, synovial fluid. Bone ends are covered with articular cartilage, united by an articular capsule and ligaments. Functional classification: Joints are classified according to the degree of movement they permit into 3 types: 1. Synarthrosis: immovable joints. 2. Amphiarthrosis: slightly movable joints. 3. Diarthrosis: freely movable joints. Fibrous joints: 3 types: 1. Sutures: e.g., sutures between flat bones of the skull ( no movement (synarthrosis). 2. Syndesmosis: bones are held together by fibrous ligaments or membranes. Example e.g. radius and ulna of forearm that are joined by interosseous membrane, slightly movable. 3. Gomphosis: cone-shaped process fits into a socket. Example: roots of teeth are held in alveolar process of maxilla and mandible by periodontal membrane. Cartilagenous joints: 2 types: 1. Synchondrosis (primary cartilagenous): 2 bones joined together by hyaline cartilage. Example: epiphyseal plate of long bones: no movement, temporary. and joint between first rib and manubrium of sternum: permanent synchondrosis 2. Symphysis (secondary cartilagenous): 2 bones joined by fibrocartilage: stronger slightly movable = amphiarthrosis provides strength and shock absorption as well as flexibility examples: IVDs and symphysis pubis (between pubic bones). Synovial joints: 6 major types based on the shape of articular surfaces and or type of movement they permit: 1. Plane (gliding): - The opposed surfaces of the bones are flat or almost flat. - They permit gliding or sliding movement. - Mono-axial. - Example: zygapophyseal (facet) joints of vertebral column, and acromioclavicular joint. 2. Hinge (ginglymus): - Convex cylinder of one bone is applied to a concavity in the other bone. - Monoaxial: movement in one plane; flexion and extension. - Bones are joined by strong collateral ligaments - Examples: interphalangeal joints, elbow, knee and ankle joints . 3. Pivot (trochoid): - Formed of a central long axis surrounded by a bony-ligamentous ring. - Monoaxial: movement is rotation around a long axis. - Example: median atlantoaxial (atlanto-odontoid) joint and proximal and distal radio-ulnar joints. 4. Condyloid (ellipsoid): - Opposing surfaces are concave and convex. - Biaxial: movements: flexion and extension adduction and abduction - Example: atlanto-occipital, and metacarpophalangeal joints. 5. Saddle = sellar: - Opposing surfaces are concavo-convex and oriented at right angles to each other. - Biaxial - Example: carpometacarpal joint of the thumb and sternoclavicular joint. 6. Ball and socket: - Spherical head of a bone is received in a socket of the other bone. - Movement is multiaxial: all directions. - Example: shoulder joint and hip joint. JOINTS OF THE CERVICAL REGION 1. Atlanto-occipital joint. 2. Atlanto-axial joints. 3. Uncovertebral joints (of Luschka). 4. Joints of the vertebral bodies: IVD 5. Joints of vertebral arches: zygapophyseal joints (z joints = facet joints). Atlanto-occipital joints: - They are synovial joints of the condyloid (ellipsoid) type - Articular surfaces: occipital condyles and superior articular facets of atlas. - Have thin, loose articular capsule lined by synovial membrane. - Biaxial joint. - Nodding of the head is the main movement at this joint (flexion and extension, approval, yes movement). - Lateral flexion of the head is also possible (adduction and abduction). Atlanto-axial joints: - There are 3 atlanto-axial synovial articulations: - Two lateral atlanto-axial joints: synovial plane joints between the articular facets of C1 and C2 - One median atlanto-axial joint: synovial pivot (trochoid joint) between the dens of C2 and the fovea dentalis of C1. A synovial pocket is also present between the dens and the transverse ligament of the atlas. - Rotation is the main movement at all the three joints (disapproval, no movement). The skull and C1 rotate on C2 as a unit. - Excessive rotation at these joints is prevented by the alar (check) ligaments. Uncovertebral joints of Luschka: - Located between the uncinate processes of C3-C7 and the small grooves on the inferior aspect of vertebral bodies above. - They are considered as small synovial joints. - They allow flexion and extension and limit lateral flexion. - They are frequent sites of spur formation that may cause neck pain due to encroachment on cervical nerves. Occipito-axial complex (syndesmosis): Four ligaments connect the occiput to the axis posteriorly: 1. Tectorial membrane: - Upward continuation of the posterior longitudinal ligament. - It extends between the body of C2 to anterior rim of foramen magnum (basilar part of occipital bone). It covers the alar, apical and cruciate ligaments. 2. The longitudinal band of cruciate ligament/cruciform ligament. The cruciate ligament is formed of: (a) Transverse ligament of the atlas: - Extends from one median tubercle on the lateral mass of the atlas to a similar tubercle on the other side. - Holds the dens against the posterior surface of the anterior arch of atlas. - Forms a synovial joint with the posterior surface of the dens. (b) longitudinal band (cranial/superior band and caudal/inferior band): - Runs from the back of body of axis to anterior rim of foramen magnum - Located posterior to the apical ligament and anterior to the tectorial membrane 3. Apical ligament (suspensory ligament of the dens): extends from the apex of the dens to the anterior rim of foramen magnum deep to the longitudinal band of cruciate ligament. 4. Alar ligaments (check ligaments): - Extend from the sides of the apex of the dens to the tubercles on the medial sides of occipital condyles. They are considered as check ligaments because they limit rotation of the head. N.B.: Accessory part of tectorial membrane: limits rotation between axis and atlas. Clinical application: significance of ADI seen on lateral cervical x-ray OTHER LIGAMENTS OF CERVICAL REGION Posterior atlanto-occipital membrane: extends between the posterior arch of atlas and posterior margin of foramen magnum (vertebral artery passes below it). Anterior atlanto-occipital membrane: extends between the anterior arch of atlas and anterior margin of foramen magnum. COMMON LIGAMENTS OF THE VERTEBRAL COLUMN (9) 1. Anterior longitudinal ligament (anterior common ligament, ALL) - It is a strong broad fibrous band that covers and connects the anterior aspect of vertebral bodies and IVDs. - It extends from the occiput and anterior tubercle of the atlas to the pelvic surface of the sacrum. It is supplied with pain fibers. - It is narrowest at its upper end and widens as it descends. - It limits extension and is frequently damaged in hyperextension injuries to the cervical region; whiplash injury. Type of articulation: amphiarthrodial syndesmosis. 2. Posterior longitudinal ligament (posterior common ligament, PLL) - It is the downward continuation of the tectorial membrane. - Much narrower and weaker than ALL. - Forms part of the anterior boundary of vertebral canal. - It extends from the posterior aspect of C2 body( anterior to spinal cord) to sacrum It is firmly attached to the back of IVDs on the sides, thus limiting posterior disc protrusion. It prevents hyperflexion of the vertebral column and herniation of IVDs. It is supplied with pain fibers. Type of articulation: amphiarthrodial syndesmosis. 3. Ligamentum flavum (yellow ligaments) - Paired ligaments (right and left) that run between laminae of adjacent vertebrae. - They form part of the posterior boundary of vertebral canal. - It extends from C1-C2 superiorly to L5-S1 inferiorly. - It is thin in cervical region, thicker in thoracic region and thickest in lumbar region. - They almost fuse with each other posteriorly. - Elastic fibers are the predominant fibers. - Functions: (1) arrest abrupt flexion of vertebral column and prevent injury to IVDs. (2) assist in extension of vertebral column after flexion (elastic fibers). (3) The elasticity prevents buckling of ligamentum flavum into the vertebral canal during extension. 4. Ligamentum nuchae=nuchal ligament (cervical region only): - It extends from the EOP superiorly to C7 spinous process inferiorly, and from cervical spinous processes anteriorly to the dermis of the skin of the back of neck posteriorly. - It is the homologue of the supraspinous ligaments in thoracic and lumbar regions. - It limits flexion of cervical spines. 5. Supraspinous ligaments - Continuation of ligamentum nuchae. - Strong fibrous cord that connects the tips of SPs together. - Extends from the tip of C7 spinous process to the S1 tubercle. - It limits flexion of the spine. 6. Interspinous ligaments - Weak, thin, membrane-like that connect adjoining spinous processes along the entire process from root to tip. - They join the ligamentum flava anteriorly and the supraspinous ligaments posteriorly. - They are well developed in the lumbar region. 7. Intertransverse ligaments: - They connect the TP of one vertebra to TP of the lower vertebra. - They are well developed in the lumbar region, in the other regions of the column, they are replaced by the intertransverse muscles. N.B. - All the ligaments are supplied with sensory afferent fibers that transmit pain sensation if any of the ligaments is stretched or damaged. - All the ligaments of the spine form syndesmosis types of joints What are the nine common ligaments of the spine? VERTEBRAL ARTERY - Closely related to cervical vertebrae. - A branch of first part of subclavian artery. - Can be divided into 4 parts: - First part: - From the subclavian artery to TP of C6. - It courses between longus colli and scalenus anterior muscle. - It is joined by the vertebral vein and sympathetic nerve plexus. - Second part: - The part that ascends through the transverse foraminae of C6-C1. - It is accompanied by the vertebral vein and a sympathetic nerve plexus. - It makes a dramatic lateral curve (45o) as it passes through TP of C2. This allows the artery to reach the more laterally placed TP of C1. - Extension with rotation of the head to one side normally impairs blood flow through the second part of vertebral artery of the opposite side. - Third part: - It begins as the artery passes through TP of C1. - It curves around superior articular process of C1, reaches posterior arch of atlas where it lies in the groove for vertebral artery separated from it by (suboccipital nerve: C1). Then, it passes below the posterior atlanto-occipital membrane that may ossify and form a bridge for the artery. - Fourth part: - Begins as the artery passes below the bridge of the posterior atlanto-occipital membrane. - It runs medially, pierces the dura mater and arachnoid mater and enters the cranial cavity through the foramen magnum. It ascends along the clivus where it joins the other vertebral artery and form the basilar artery at the lower border of the pons. - Branches of the 4th part of vertebral artery (1) Posterior meningeal artery (2) Anterior spinal artery: arises from each vertebral artery and then unite into one anterior spinal artery which supplies the anterior aspect of spinal cord. (3) Posterior spinal arteries: one branch from each vertebral artery. They course parallel to each other and supply the posterior aspect of the spinal cord. (4) Posterior inferior cerebellar arteries (PICA): supply the cerebellum. George?s test: Evaluates the patency of vertebral arteries in all clinical cases of cervical spine: rotation and extension of the head( dizziness, tennitus and vertigo (positive test). BASILAR ARTERY - Formed at the lower border of the pons by union between the two vertebral arteries. - Gives the following branches: Anterior inferior cerebellar arteries (AICA). Labyrinthine (inner ear) arteries. Pontine arteries. Superior cerebellar arteries. Posterior cerebral arteries: are the two terminal branches of the basilar artery and participate in the formation of arterial circle of Willis. ARTERIAL CIRCLE OF WILLIS - It supplies the brain. - Formed by the anastomosis between branches of 4 main arteries: 2 internal carotid arteries and 2 vertebral arteries. - Located on the inferior surface of the brain and is formed of: 2 posterior cerebral arteries. 2 posterior communicating arteries. 2 internal carotid arteries. 2 anterior cerebral arteries. One anterior communicating artery. Clinical considerations: Decreased blood supply of the brain by embolism, thrombosis or hemorrhage may lead to sudden onset of neurological symptoms( stroke. Thus, if one of the four main arteries supplying the brain is blocked, little exchange of blood takes place, especially in old people leading to vascular stroke. Transient ischemic attacks (TIA): Episodes of vascular insufficiency that cause temporary loss of brain function, with total recovery within 24 hours. Most attacks follow lodgment of fibrin clots or detached atheromatous tissue at an arterial branch point with subsequent dissolution. Transient symptoms may include motor weakness (a heavy feeling) in an arm or leg, hemisensory deficit (a numb feeling), blindness of one eye, vertigo, ataxia, amnesia Recognition of TIAs is important, because they serve notice of impending heart attacks and strokes Without treatment, one patient in four will die from a heart attack within 5 years, and one in six will suffer a stroke THORACIC (DORSAL) VERTEBRAE - Twelve in number and their size increases caudally. - They are attached to the ribs. - They have two characteristic features: Possess costal facets on the sides of the body to articulate with the heads of ribs. Possess costal facets on the TPs of T1-T10 to articulate with the tubercles of ribs. RIBS: vertebral end:(head, neck, tubercle), angle, shaft, and sternal end. (Plate 186) TYPICAL THORACIC VERTEBRAE: T2-T8 Vertebral body: - Heart-shaped. - Body has two pairs of costal demifacets; the upper pair is near the pedicles and the lower pair is anterior to inferior vertebral notch (thus the body articulates with two ribs;the corresponding rib and the rib below). Pedicle: is short and shows a shallow superior vertebral notch (groove) and a deep inferior vertebral notch. Laminae: short, broad and thick. Spinous process: long, directed obliquely downward. SPs of T5-T8 overlap the most. Transverse processes: - Thick and strong. - Arise from the neural arch posterior to the superior articular process. - Their costal elements developed into ribs. - Have a costal facet on their anterior aspect for articulation with the tubercle of the rib except T11 and T12. Articular processes: (oriented in coronal plane) - The superior articular processes (pre-zygapophyses) arise from lamina-pedicle junction and extend vertically upward and face posteriorly. - The inferior articular processes (post-zygapophyses) arise from inferior surface of laminae and extend vertically downward and face anteriorly. Vertebral foramen (neural ring): small and circular. ATYPICAL THORACIC VERTEBRAE: T1,9,10,11 and 12 T1 (transitional vertebra): - Vertebral body has one upper pair of full facets and a lower pair of demifacets. - Has a small uncinate process that is usually found on cervicals. - Has a superior vertebral notch (not a groove). - In 33% of population, T1 is the vertebra prominens instead of C7. T9: has one or 2 pairs of costal demifacets, making it articulate with the ninth or ninth and tenth pairs of ribs. T10: has one pair of full costal facets that articulate with the tenth pair of ribs only. T11(transitional vertebra): - Has one pair of full costal facets that articulate with the eleventh ribs only. - Has no transverse costal facets. - The body approaches that of lumbar vertebrae (transitional). - the spinous process is short, club-shaped with no overlapping. T12 (transitional vertebra): - Has one pair of full costal facets for the 12th ribs. - Has no transverse costal facets. - Post-zygapophysis (inferior articular process) faces laterally (sagittal plane) like lumbar vertebrae (unlike all other thoracic vertebrae where it faces anteriorly: coronal plane). - TP is short and knob-like and has 3 tubercles that are homologous of the following lumbar processes: Superior tubercle of T12 is the homologue of lumbar mamillary process. Inferior tubercle of T12 is the homologue of lumbar accessory process. Lateral tubercle of T12 is the homologue of lumbar transverse process. - SP is also short, club-shaped with no overlapping. To summarize: Each side of thoracic vertebral bodies shows the following costal facets: T1: one full facet and one demifacet. T2- T8: 2 demifacets. T9: one or two demifacet. T10-T12: one full facet. Clinical application: scoliosis and kyphosis COSTOVERTEBRAL ARTICULATIONS 1. Costovertebral (costocorporeal) articulations: - Synovial plane (gliding) joints: between head of a rib and two adjacent vertebral bodies and intervening IVD (typical thoracic vertebrae) or one vertebral body (atypical vertebrae). - The rib head articulates with the superior demifacet of the same number vertebra and the inferior demifacet of the vertebra above. - Articular capsule: attaches at the margins of articular surfaces. Movement: slight gliding movement and rotation. - Ligaments of the joint: Radiate ligament; ligament of the head (from T1-T12): fans out from the anterior aspect of the head of the rib to the sides of the two vertebral bodies and IVD between them. Intra-articular ligament (from T2-T9): between the crest of the head of the rib and the IVD thus dividing the joint into 2 synovial cavities. 2. Costotransverse joints: - Synovial gliding (plane) joints, between the tubercle of a rib and the TP of the corresponding vertebra. Do not exist in the 11th and 12th ribs. - Articular capsule: attaches at the margins of articular surfaces - Ligaments of the joint: Costotransverse ligament: from the posterior aspect of the neck of the rib to the anterior aspect of adjacent TP (anterior to the joint). Lateral costotransverse ligament (ligament of tubercle): short , strong between tubercle of the rib (non-articular part) to the tip of corresponding TP (posterior to the joint). Superior costotransverse ligament: From the sharp crest on the upper border of the neck of the rib to the lower border of the TP superior to it. It is divided into 2 parts; anterior and posterior. All those ligaments are present from T1- T10. Movement: slight gliding movement and rotation. LUMBAR VERTEBRAE - The lumbar vertebrae (5) are in the lower back (small of the back). - They are characterized by massive bodies (carrying the weight of the body except the lower limbs), strong laminae, absence of costal facets and transverse foramina. - 80% of individuals will have low back pain during their lifetime. - The annual cost related to low back pain is $ 100 billion in the USA alone. - The most common causes of low back pain are the lumbar zygapophyseal joints and IVDs. - The highest point of iliac crest is at the level of L4, while umbilicus is at L3/L4 IVD. - The first four lumbar vertebrae are typical, the 5th is atypical or peculiar. TYPICAL LUMBAR VERTEBRAE: Vertebral bodies: - Large, kidney-shaped. - Their transverse diameters are larger than their antero-posterior diameters. - Thicker anteriorly than posteriorly(lumbar lordosis. Pedicles: - Short, strong (transfer body weight to vertebral arch). - Shallow superior vertebral notch and deep inferior vertebral notch. Transverse processes: - Project posterolaterally from pediculolaminar junction. - Lumbar TPs are quite long, the TPs of L3 being the longest while TPs of L5 are the strongest. - They have no costal facets nor transverse foramina. - Their anterior aspects are the costal elements and may develop into ribs. Accessory processes: - Located on the inferior aspect of the base of TPs. - Serve for attachment of longissimus muscle and medial intertransverse muscles. Superior articular processes: face medially and posteriorly(oriented in sagittal plane) Mamillary processes: Project from the posterior aspect of the superior articular processes, serve as sites of origin of multifidus muscles. Inferior articular processes: Face laterally and anteriorly and fit in the superior articular processes of the vertebrae below. This articulation (Z joint) allows flexion and extension and limits rotation in lumbar spine (oriented in sagittal plane). Spinous processes: - Long, strong, club-shaped, flat and rectangular. - Project directly horizontal. - Give attachment to muscles and ligaments. Laminae: - Broad, thick and short. - The region of the lumbar laminae located between the superior and inferior articular processes is known as: pars interarticularis. This part is frequently fractured causing a condition known as spondylolysis. This may lead to anterior displacement of vertebral bodies, pedicles, TPs and superior articular processes. This condition is known as spondylolisthesis. - Spondylolysis and spondylolithesis are most common at L5. - The consequence is spinal canal stenosis or nerve compression( radicular pain. Vertebral foramen: moderate size and triangular ATYPICAL LUMBAR VERTEBRA (L5): 1- Has the greatest circumference of all lumbars. 2- Its body is wedge-shaped; thicker ventrally than dorsally( prominent lumbosacral angle. 3- The spinous process is the shortest of all lumbars and has a rounded tip. 4- The distance between the inferior articular processes is wider than other lumbars. 5- The inferior articular processes are oriented in the coronal plane. INTERVERTEBRAL JOINTS (IVDs) - Secondary cartilaginous joints (symphyses, amphiarthrodial) designed for weight-bearing, strength and shock absorption - The IVDs are named for the vertebra above e.g. T6 disc is between T6-T7 thoracic vertebrae. They are thicker in cervical and lumbar regions than in thoracic region. - The IVDs form part of the anterior boundary of IVFs. - The IVDs act as shock absorbers, but their main function is to bind vertebral bodies. - They are thicker anteriorly than posteriorly in the cervical and lumbar regions( secondary curves of vertebral column. - The cartilagenous end plates (CEP) that cover vertebral bodies are connected to IVDs. - There are 23 IVDs, the first one is between C2-C3 and the last one is between L5-S1. - A small IVD is located between the sacrum and the coccyx - The IVDS are reinforced by the attachment of the ALL and PLL. - Each IVD consists of 2 components: Anulus fibrosus (AF): Weight bearing - It is formed of concentric lamellae (12-20), the outer are collagenous fibers type I and the inner are fibrocartilage. Each lamella makes 120o angle with the previous lamella( criss-cross pattern (resist compression forces). - The anterior aspect of AF is stronger than the posterolateral aspect which is weak and most liable to protrusion and herniation. - The lamellae of AF may tear circumferentially; separation of adjacent lamellae, or radially; from deep fibers of AF to superficial fibers. Both tears may lead to bulging (protrusion) of NP or herniation (prolapse)( low back pain. (2) Nucleus pulposus (NP): Shock absorption - It is the central portion of the disc (remnant of the embryonic notochord). - It is soft, pulpy, gel-like mass. It fills 30-50% of total disc area. - Its water content is 70-90% and the rest is collagen fibers, cells (notochord cells, fibroblasts & chondrocytes) and ground substance(proteoglycans), mainly glucosaminoglycans (GAGs) as chondroitin sulphate. It is thickest in lumbar spine, followed by cervical region and thinnest in thoracic spine What is the effect of loads on the IVD? - The main function of GAGs is to provide support and transport water (imbibition)and nutrition to IVD. Its gel-like nature( shock absorber. - The water content of the nucleus pulposus continually decreases with age (88% at birth and 70% at the age of 70 years) because of decrease in GAGs. - It acts like a shock absorber for axial forces and like a semifluid ball yeilding during flexion, extension, rotation and lateral flexion. - What do you know about Schmorl?s nodes? Cartilagenous end plate (CEP): Nutrition A thin strip of hyaline cartilage (1-3mm) that covers the upper and lower surfaces of vertebral bodies and is firmly attached to AF. It provides support, resilience, distribution of forces and nutrition. Nerve supply of the IVD - The outer 1/3 of AF is provided with pain fibers from: sympathetic trunk ganglia: anteriorly. gray rami communicans: laterally and postrolaterally. recurrent meningeal nerve (sinovertebral nerve): posteriorly. Ventral primary rami of spinal nerves: laterally. Triad of x-ray findings in disc degeneration: - Disc narrowing. - Osteophytes (bone spurs): new bone formation at the edges. - Sclerosis of cartilagenous end plates (CEP). Ligaments attached to IVDs: - ALL: innervated by sympathetic ganglia. - PLL: innervated by recurrent meningeal nerves Relationship of spinal nerves to IVDs - The first seven spinal nerves exit through IVFs above the vertebra of the same number e.g. C5 exit through C4-C5 IVF. - The 8th cervical spinal nerve exits IVF below C7. - All spinal nerves below C8 nerve exit below the corresponding vertebrae e.g. T5 nerve exits through T5-T6 IVF. - Clinically: - disc herniation at C3-C4 affects C4 nerve. - disc herniation at T3-T4 affects T3 nerve. - disc herniation at L3-L4 affects L4 nerve roots Clinical considerations Vibration of the spine (truck drivers, more than 3 hours/day) may cause fatigue failure of AF( disc prolapse (more common in middle age)( back pain. Osteoarthritis: degenerative disease of the spine in old age( disc degeneration( back pain. Disc protrusion: is defined as a radial tear in AF posteriorly or posterolaterally with migration of the nucleus pulposus through the tear causing the posterior border of the anulus to bulge into the neural canal. This condition may cause compression of the nerve root and is characterized by back pain as the chief complaint and leg pain occurring later. These are aggravated by coughing,sneezing and strainig at the stools. A positive Valsalva?s maneuver is also noted. Disc prolapse: a radial tear in the anulus posteriorly or posterolaterally through which a piece of nuclear tissue migrates into the neural canal. The chief complaint is leg pain with minimal or no back pain. The patient presents with negative Valsalva?s maneuver because of loss of the nuclear tissue and a corresponding loss of pressure. A marked antalgia (patient presents a posture that minimizes his pain) is obvious together with root compression signs. FACET JOINTS ( Z joint/ zygapophyseal / apoghyseal / interlaminar joints) - Synovial plane (gliding) diathrodial joints between superior and inferior articular processes of adjacent vertebrae. - The Z joints permit gliding movement between vertebrae - The articular surface is covered by hyaline articular cartilage forming articular facets. - Each joint is surrounded by a thin loose articular capsule, which is attached to the margins of articular surfaces. Anteriorly the ligamentum flavum takes the place of the joint capsule. - The articular capsule is lined by synovial membrane. The capsule and synovial membrane extend into the joint cavity and cover part of the articular cartilage (synovial folds or menisci). - The shape and orientation of articular facets determine the type of movement in each region of the vertebral column. (remember that the superior articular facets in the cervical region are directed mainly posterosuperiorly and the inferior articular facets are directed anteroinferiorly; those in the thoracic region are directed mainly posteriorly and anteriorly respectively (oriented in coronal plane) and those in the lumbar region are directed mainly medially and laterally respectively (oriented in sagittal plane). - Normally the pain-sensitive articular capsule and synovial membrane are held out of the joint space by: a. Multifidus muscles: which arise from the mamillary process and posterior aspect of each capsule and pulls the capsule out of the joint?s posterior aspect. b. Ligamentum flavum: pulls the synovium out of the joint?s anterior aspect. Innervation of zygapophyseal joints: - Rich nerve supply for the articular capsule, synovial membrane, synovial folds. - From the medial branch of dorsal primary rami of spinal nerves of same level and one level above and below: thus pain from a Z joint has a very broad referral pattern. Clinical considerations: The z joints could be the source of back pain since they are richly supplied with pain fibers and can undergo degenerative changes (osteoarthritis) leading to osteophyte formation( compression of existing spinal nerve ( back pain. Interaction between zygapophyseal joints and IVDs: Aging leads to degeneration of IVDs which leads to increased stress on Z joints (normally the disc absorbs most of the compression forces of the spine). This results in pain from pressure on the synovial folds (menisci) being caught between the articular facets. SACRUM A large triangular wedge-shaped bone. - It is wedged between the hip bones. Consists of 5 fused segments in adults. In early life, the 5 sacral segments are separated by hyaline cartilage which ossifies at the age of 25 years. - It provides strength and stability to the pelvis and transmits the weight of the body to the pelvic girdle through the sacroiliac joints. - The sacrum articulates with the iliac bones laterally, coccyx inferiorly and the 5th lumbar vertebra superiorly. - The sacrum is tilted anteriorly so that it articulates with L5 vertebra at the lumbosacral angle. - The different parts of the sacrum are: base, apex, pelvic surface, dorsal surface and 2 lateral surfaces. Base: - It is formed of the first sacral segment (S1). - It has a large body, anterior projecting lip known as sacral promontory (important obstetrical landmark) and 2 lateral masses known as the alae of the sacrum. - The alae (wings) of sacrum are formed by fusion of the costal elements anteriorly and the TPs posteriorly. - The vertebral foramen of the first sacral segment is triangular and forms the beginning of the sacral canal. - The pedicles are small and lead to the laminae which meet posteriorly to form the first sacral spinous tubercle. - The superior articular processes articulate with the inferior articular processes of L5 vertebra and are oriented in the coronal plane. Apex: - It is the tapering inferior end of the sacrum. - It has an oval facet for articulation with the coccyx. Pelvic surface: - Smooth and concave. - Presents 4 transverse ridges (indicate fusion of the 5 sacral segments). - The ridges end at anterior sacral foramina (4 on each side), through which exit the ventral primary rami of S1-S4 spinal nerves (plate 497). Dorsal surface: - Rough and convex. - Presents 5 prominent longitudinal ridges. - The median sacral crest (collective name of 4 sacral spinous tubercles) represents the fused spinous processes of the upper 4 sacral segments (S5 has no spinous process( the only naturally occurring spina bifida, due to failure of fusion of laminae of S5 segment( sacral hiatus at lower end of sacral canal). - The medial (intermediate) sacral crests (2) represent the fused articular processes of S2-S5. The 5th articular processes extend inferiorly( sacral cornua on either side of the sacral hiatus. - The lateral sacral crests (2) represents the fused TPs of the five sacral segments. - Sacral tuberosity: an elevation on upper lateral part of the dorsal surface. - Sacral fossae: upper, middle and lower; lateral to lateral sacral crest. - Four pairs of posterior sacral foramina are located lateral to the intermediate sacral crest. They allow the exit of the dorsal primary rami of upper 4 sacral spinal nerves. - The sacral hiatus contains fatty tissue, filum terminale, S5 nerve and coccygeal nerve. - Clinically, the sacral cornua are important landmarks for locating the sacral hiatus used for induction of sacral epidural anesthesia. Lateral surface: - Is composed of the fused TPs of all sacral segments. - Presents an upper articular surface that looks like an ear( auricular surface for articulation with the articular surface of the ilium( synovial part of sacroiliac joint. - Inferior to the auricular surface, the lateral surface of the sacrum becomes narrow and presents inferior lateral angle, below which the sacrum rapidly tapers to sacral apex. - Below the angle is a notch which is converted into a foramen by the TP of the first coccygeal segment and the lateral sacrococcygeal ligament. This is the last or 31st IVF. Sacral canal: - It is triangular, it starts at vertebral foramen of S1 segment and ends at the sacral hiatus. - It does not contain the spinal cord which ends at L2. It contains the sacral and coccygeal nerves, filum terminale, dura and arachnoid mater, venous plexuses, lateral sacral arteries and lymph vessels N.B.: - Fusion of L5 vertebra with the sacrum( sacralization (sacrum 6 segments). Separation of S1 segment from sacrum and its fusion with L5( lumbarization (6 lumbar vertebrae). Sex difference of sacrum Female sacrum is: - Wider( wider pelvic inlet(more space for passage of fetal head during labor. - Shorter( wide pelvic outlet. - Pelvic surface is more curved( more pelvic space. - Larger lumbosacral angle (sacral promontory is more bulging anteriorly in males). COCCYX (Tail bone) - Small triangular bone. - Formed usually by 4 fused segments. - It has a base, apex, pelvic surface, dorsal surface and lateral borders. - The base is formed of an oval concave facet on the body of the first segment that articulates with the body of S5 segment. - The apex is only a small tubercle at the bottom of vertebral column. - The ventral surface is smooth and concave. - The dorsal surface is irregular and convex. - Co. segment #1 is the largest and broadest. Its short TPs are connected to the sacrum forming the last IVF and its rudimentary articular processes form coccygeal cornua. - The coccyx does not participate in support of body weight but provides attachment for gluteus maximus and coccygeus muscles and anococcygeal ligament and filum terminale externum (coccygeal ligament) PELVIS - It is the lower part of the trunk and its skeleton is referred to as the bony pelvis. - The bony pelvis is made up of: two hip bones, sacrum and coccyx. HIP (COXAL) BONE = OS COXAE=INNOMINATE BONE - The two hip bones articulate with each other anteriorly at the symphysis pubis, posteriorly with the sacrum at two sacroiliac joints. - The hip bone is formed of 3 parts: ilium, ischium and pubis. The three parts are fused at the acetabulum which is located on the external surface of hip bone. - The pelvic girdle, formed by the hip bones and sacrum transmits the weight of the body to the lower limbs. Ilium: - The superior, flattened, fan-shaped part of the hip bone. - The alae of the ilium represent the spread of the fan and the body represents the handle. - The body of the ilium shares in the formation of the acetabulum. - The iliac crest: the rim of the fan, it extends between the anterior and posterior superior iliac spines (ASIS and PSIS). The iliac crest has an external lip and an internal lip. The highest point of iliac crest is at the level of L4. - The iliac tubercle is a notable prominence on the external lip, 6 cm behind ASIS It is at the level of L5 (transtubercular plane). - Anterior inferior iliac spine (AIIS): a prominence above the acetabulum. - Posterior inferior iliac spine (PIIS): downward continuation of the PSIS. - Greater sciatic notch: where ilium and posterior border of ischium meet. - Gluteal surface (dorsal surface): located between acetabulum and iliac crest and presents 3 gluteal lines: a. Anterior gluteal line: from the greater sciatic notch to ASIS. b. Posterior gluteal line:begins above PIIS to external lip of iliac crest. c. Inferior gluteal line: from the greater sciatic notch toward the AIIS. - Iliac fossa: smooth concave pelvic surface of the ilium. - Sacropelvic surface: shows an auricular surface which articulates with the auricular surface of the sacrum to form the synovial part of sacroiliac joint. and an iliac tuberosity: a rough area posterior to the auricular surface. - Iliopubic eminence: marks the junction of pubic and iliac bones (below and medial to AIIS). - Arcuate line: separates true from false pelvis. Ischium: - It is the strongest part of the hip bone. - L-shaped, formed of a body that shares in the formation of the acetabulum and a ramus that shares in the formation of obturator foramen (largest foramen in the body). - Ischial tuberosity: large irregular area between body and ramus and supports the weight of upper body while sitting, attached to sacrotuberous ligament - Ischial spine: is a small pointed posterior projection between greater and lesser sciatic notches, attached to sacrospinous ligament - Lesser sciatic notch: between ischial spine and ischial tuberosity. (3) Pubis: - An angulated bone with a superior ramus that helps to form the acetabulum and an inferior ramus that helps form the obturator foramen. - Body of the pubis is flattened and has a smooth pelvic surface and a rough oval medial surface which articulates with the other pubic bone at symphysis pubis. - Pubic crest: thickened anterior part of the body - Pubic tubercle: the projecting lateral aspect of the pubic crest. - Pecten pubis = pectineal line: oblique ridge on superior pubic ramus between pubic tubercle and iliopubic eminence (together with arcuate line of ilium they form ileopectineal line which separates true from false pelvis) N.B.: - The acetabulum is a rounded pit on the lateral aspect of the hip bone. It is formed by the 3 parts of the hip bone. It articulates with the head of femur and shows an acetabular notch and an acetabular fossa. The pelvic brim: is formed by sacral promontory, alae of sacrum, iliopectineal line, pubic crest and pubic symphysis. It forms the inlet to the true pelvis. PELVIC JOINTS AND LIGAMENTS The joints of the pelvis are the lumbosacral joints, the sacrococcygeal joint, the pubic symphysis and the sacroiliac joints. Lumbosacral joints (3) - L5-S1 articulate anteriorly through the 23rd IVD. - L5-S1 articulate posteriorly through 2 zygapophyseal (facet) joints. The facets on S1 (oriented in coronal plane) face posteriorly, thus preventing L5 from sliding anteriorly. - Iliolumbar ligament: extends between TP of L4 and L5 and iliac crest. It helps to stabilize lumbosacral joints and is considered an accessory ligament to SIJ. Sacrococcygeal joint - Between apex of sacrum and base of coccyx. - A secondary cartilagenous joint (has a fibrocartilagenous IVD) - Reinforced by anterior and posterior sacroccocygeal ligaments. Symphysis pubis: - Between medial surfaces of bodies of pubic bones in the median plane. - A secondary cartilagenous joint with a fibrocartilagenous interpubic disc. - Reinforced by superior and inferior pubic ligaments. Sacroiliac joints (SIJ) - Diseases of SIJ account for 20% of low back pain. - Strong, weight bearing, atypical synovial joints between the auricular articular surfaces of the sacrum and ilium and sacral and iliac tuberosities. - These surfaces have irregular elevations and depressions that produce some interlocking of the bones. The lower anterior part of the joint is synovial and the upper posterior part is fibrous (syndesmosis). - Ligaments of SIJ: main ligaments are Articular capsule: - Located only along the anterior surface of the joint. - Lined with a synovial membrane. - innervated with nociceptive and proprioceptive fibers. Interosseous sacroiliac ligament: connects the iliac and sacral tuberosities. Anterior sacroiliac ligament: covers the anterior aspect of SIJ horizontally. Posterior sacroiliac ligaments: - Much stronger than the anterior sacroiliac ligament. - Formed of 2 parts: a. Short posterior sacroiliac ligament: extends horizontally between S1 and S2 sacral tubercles to iliac crest and iliac tuberosity. b. Long posterior sacroiliac ligament: extends vertically between PSIS and S3 and S4 sacral tubercles. - Accessory sacroiliac ligaments: The stability of SIJ is enhanced by three accessory ligaments: Sacrospinous ligament: extends between pelvic (anterior) surface of the sacrum to ischial spine. The greater sciatic foramen is superior to this ligament. Sacrotuberous ligament: extends between the dorsal inferior aspect of the sacrum and ischial tuberosity. The lesser sciatic foramen is formed between this ligament and sacrospinous ligament. (3) Iliolumbar ligament (page 27) - Innervation of SIJ: It is richly innervated anteriorly by ventral primary rami of L2-S2 spinal nerves and posteriorly by dorsal primary rami of L4-S3 spinal nerves( wide range of pain referral pattern. - Movement at SIJ: Movement is limited because of the interlocking of the articulating bones and the thick interosseous and posterior sacroiliac ligaments. Movement are: nodding, rotation and gapping. The main function of SIJ is to provide stability and to transmit the body weight to the lower limbs. N.B.: Relaxation of pelvic joints and ligaments occur during pregnancy and labor under the effect of female hormone( increase pelvic diameters by 10-15%. Clinical correlation: SIJs receive stress from below while sitting, e.g. driving on poorly maintained roads in a vehicle with poor suspension. Women are more susceptible than men to SIJs problems; hormone relaxin is secreted during menstruation, pregnancy and after labor. Chiropractic management (a regimen of manipulations) is used to treat SIJs disorders with about 90% improvement rates. What do you know about Ankylosing spondylitis? Patient sex:?????? Age:????????????????. Complaint:???????????????? Cause:??????????????????. Presentation:????????????????.. X-ray findings:???????????????? Consequencies:????????????????. MUSCLES OF THE BACK They are arranged in 6 layers: LAYER I: 2 muscles: Trapezius. Latissimus dorsi. These muscles connect the upper limb with the spine. TRAPEZIUS: A triangular muscle that covers the posterior portion of neck and upper portion of back. - Origin: More stable, wider attachment, more medial. - EOP and medial 1/3 of superior nuchal line. - Ligamentum nuchae. - Supraspinous ligaments of thoracic region. - Spinous processes of C7-T12. - Insertion: Mobile, narrow attachment, laterally situated. - Upper fibers: lateral 1/3 of the clavicle. - Middle fibers: acromion and spine of scapula. - Lower fibers: spine of scapula. - Nerve supply: - Motor: Spinal accessory: CN XI (motor). - Sensory: C3 and C4: proprioception (sense of position in relation to the body). - Action: Shoulder elevation (upper fibers). Shoulder retraction = retraction of scapula (middle fibers). Shoulder depression (lower fibers). If the scapula is stabilized: Unilateral contraction( extension of head, rotation of face( opposite side. Bilateral contraction( extension of head and neck. Arm abduction : 0o - 20o: supraspinatus 20o - 90o: deltoid 90o -180o: trapezius/serratus anterior (rotation of the scapula). LATISSMUS DORSI (swimmer?s muscle): Large triangular muscle that covers the lower ½ of thoracic and the lumbar regions. - Origin: Extensive: - SPs of T7-T12. - SPs of L1-L5. - Sacral tubercles. - Supraspinous ligaments. - Thoracolumbar fascia. - Iliac crest. - Lower 4 ribs. - Inferior angle of scapula (could be insertion). - Insertion: The fibers pass upwards and laterally to be inserted into the floor of bicipital groove of humerus (intertubercular sulcus). - Nerve supply: Thoracodorsal nerve: C6, C7, C8 (brachial plexus). - Action: Medial rotation. (2) Adduction. (3) Extension. (4) It also raises the body towards the arm during climbing. Triangle of auscultation: Boundaries: - Medially: trapezius. - Laterally: medial border of the scapula. - Inferiorly: latissmus dorsi. - Auscultation of posterior segments of the lung( breath sounds are best heard in the 6th intercostal space: when folding the arm across the chest and flexing the trunk, thus enlarging the triangle and parts of 6th and 7th ribs become subcutaneous. Lumbar triangle of Petit: Boundaries: - Medially: latissmus dorsi. - Laterally: external oblique muscle. - Inferiorly: iliac crest. LAYER II: 3 muscles that connect the scapula to the spine Levator scapulae. Rhomboid minor. Rhomboid major. LEVATOR SCAPULAE: - Origin: Posterior tubercles of TPs of C1-C4. - Insertion: Medial border of scapula above the root of the spine (superior angle). - Nerve supply: Dorsal scapular nerve: C5. - Action: - Elevates scapula. - Retracts (adducts) the scapula. RHOMBOID MINOR: - Origin: - Lower part of ligamentum nuchae. - SPs of C7 and T1. - Insertion: Medial border of the scapula at the root of the spine. - Nerve supply: Dorsal scapular nerve: C5. - Action: Retraction (adduction) of the scapula. RHOMBOID MAJOR: - Origin: - SPs of T2-T5. - Supraspinous ligaments. - Insertion: Medial border of scapula below the root of the spine. - Nerve supply: Dorsal scapular nerve: C5. - Action: Retraction (adduction) of the scapula. LAYER III: 2 muscles: Accessory Muscles of Respiration Serratus posterior superior. Serratus posterior inferior. SERRATUS POSTERIOR SUPERIOR: Thin quadrangular muscle - Origin: - SPs of C7-T3. - Supraspinous ligaments. - Insertion: The fibers run downward and laterally and insert into 2-5 ribs. - Nerve supply: Ventral primary rami of T2-T5 spinal nerves (upper thoracic nerves). - Action: Raises the ribs during forced inspiration. SERRATUS POSTERIOR INFERIOR: Thin quadrangular muscle - Origin: - SPs of T11-L2. - Supraspinous ligaments. - Insertion: The fibers run upwards and laterally and insert into 9-12 ribs. - Nerve supply: Ventral primary rami of T9-T12 spinal nerves (lower thoracic nerves). - Action: Depresses the last four ribs during forced expiration. LAYER IV: 2 muscles at the back of the neck SPLENIUS CAPITIS: - Origin: - Lower ½ of ligamentum nuchae. - SPs of C7-T3. - Insertion: The fibers pass upwards and laterally to: - Mastoid process of temporal bone. - Lateral 1/3 of superior nuchal line of occipital bone. - Nerve supply: Dorsal primary rami (DPR) of spinal nerves; segmental. - Action: - Bilateral: extension of the head and neck. - Unilateral: rotate the face to the same side. SPLENIUS CERVICIS: - Origin: SPs of T3-T6. - Insertion: TPs of C1-C4 (posterior tubercles, deep to the origin of levator scapulae). - Nerve supply: DPR; segmental. - Action: - Bilateral: extension of the neck. - Unilateral: rotation of the neck to the same side. THORACOLUMBAR FASCIA (LUMBODORSAL FASCIA) - It extends from thoracic region to sacrum. - It is thin in the thoracic region. - In the lumbar region it is very strong and is composed of 3 layers: a. The posterior layer attaches to the lumbar SPs, interspinous ligaments and median sacral crest and covers and gives origin to the erector spinae muscles. . b. The middle layer attaches to the tips of TPs and intertransverse ligaments and extends superiorly from the iliac crest to the last rib and covers the posterior surface of quadratus lumborum muscle c. The anterior layer covers the anterior surface of quadratus lumborum muscle and attaches to the anterior surfaces of lumbar TPs. The posterior and middle layers surround the erector spinae muscles and meet laterally where they join the anterior layer and give origin to 3 muscles. - The thoracolumbar fascia gives origin to 4 muscles: Erector spinae muscles. Latissmus dorsi muscles. Transversus abdominis muscles. Internal oblique muscles. - Clinically: - Injury to the erector spinae muscles leads to edema and swelling in the closed compartment between the posterior and middle layers of this fascia( back pain and straightening of lumbar lordosis. - Injury to quadratus lumborum muscle may cause similar back pain since it is enclosed between anterior and middle layers of thoracolumbar fascia LAYER V: - Largest group of back muscles. - Known as the erector spinae group of muscles or sacrospinalis muscle. - A large and strong muscle that lies in a groove lateral to the spinous processes and covered by thoracolumbar fascia. - Divided into 3 columns: Iliocostalis (lateral column). Longissimus (intermediate column). Spinalis (medial column). Each column is divided into 3 parts corresponding to the segmental area in which they are located. (1) ILIOCOSTALIS: (lumborum, thoracis and cervicis) a. Iliocostalis lumborum: (I. lumborum) - It is the most lateral part of erector spinae muscles. - Origin (common origin of erector spinae): - SPs and supraspinous ligaments of T11-L5. - Median sacral crest. - Posterior surface of the sacrum. - Iliac crest. - Thoracolumbar fascia (posterior layer). - Insertion: Lower border of angles of lower 6 ribs. - Action: Extension and lateral flexion of lumbar spine, it draws the ribs down. b. Iliocostalis thoracis: - Origin: Angles of lower 6 ribs medial to insertion of I. lumborum. - Insertion: Angles of upper 6 ribs. - Action: Extension and lateral flexion of thoracic spine, it draws the ribs down. c. Iliocostalis cervicis: - Origin: Angles of 3- 6 ribs. - Insertion: TPs of C4-C6 (posterior tubercles). - Action: Extension and lateral flexion of cervical spine. - Nerve supply of iliocostalis muscles: dorsal primary rami of spinal nerves (segmental). (2) LONGISSIMUS MUSCLES: (thoracis, cervicis and capitis) Located medial to iliocostalis muscle. Largest of erector spinae muscles. It is a very long muscle (from sacrum to mastoid process; hence the name) a. Longissimus thoracis: - Origin: - Arises from the common origin of erector spinae muscles. - In addition, many fibers originate from TPs and accessory processes of lumbar vertebrae. - Insertion: - 3-12 ribs (between angles and tubercles). - TPs of T1-T12. - Action: - Bilateral contraction( extension of thoracic and lumbar vertebrae. - Unilateral contraction( laterally flexes the spine. b. Longissimus cervicis: - Origin: TPs of T1-T5 thoracic vertebrae. - Insertion: TPs of C2-C6 vertebrae (posterior tubercles). - Action: Extension of cervical spine (bilateral) or lateral flexion of the neck (unilateral). c. Longissimus capitis: - Origin: TPs of T1-T5 and APs of C4-C7. - Insertion: Mastoid process. - Action: Extension of the head (bilateral) or lateral bending of head and rotation of the face to same side (unilateral). Nerve supply of longissimus muscles: dorsal primary rami of segmental nerves. (3) SPINALIS: (thoracis, cervicis and capitis) Located medial to longissimus muscle. a. Spinalis thoracis: - Origin: SPs of T11-L2 vertebrae. - Insertion: SPs of T4-T8 vertebrae. b. Spinalis cervicis: - Origin: SPs of C7-T2 and lower part of ligamentum nuchae. - Insertion: SPs of C2-C4 vertebrae. c. Spinalis capitis (usually fuses with semispinalis capitis): - Origin: TPs of C7-T7 and APs of C4-C6. - Insertion: Occipital bone between superior and inferior nuchal lines. - Action of spinalis muscles: Extension of vertebral column. - Nerve supply of spinalis muscles: DPR of spinal nerves (segmental). LAYER VI: Occupies the groove between TPs and SPs - The deepest layer of back muscles is called the transversospinalis group which arises from the transverse processes and runs upward and medially to insert into the spinous processes. - It includes the semispinalis, multifidus and rotatores from superficial to deep. - All of them rotate the spine to the opposite side. (1) SEMISPINALIS: (thoracis, cervicis and capitis) a. Semispinalis thoracis: - Origin: TPs of T7-T12 vertebrae. - Insertion: SPs of C6-T4 vertebrae. b. Semispinalis cervicis: - Origin: TPs of T1-T6 and APs of C4-C7 vertebrae. - Insertion: SPs of C2-C5 vertebrae. c. Semispinalis capitis: Thick and strong muscle. - Origin: TPs of T1-T6 and APs C4-C6 vertebrae. - Insertion: Occiput between superior and inferior nuchal lines. - Nerve supply of semispinalis muscles: DPR of local spinal nerves (segmental). - Action of semispinalis muscles: Extension of vertebral column and head respectively and rotate them to the opposite side. N.B.: Semispinalis capitis is the most powerful extensor of the head. (2) MULTIFIDUS MUSCLES: - Lie deep to semispinalis muscle and fill the gap between the TPs and SPs of vertebrae (4 parts; lumborum, thoracis, cervicis and capitis). - Formed of many fasciculi, extend from the sacrum to SP of C2. - Best developed in the lumbar region (multifidus lumborum). - Origin: Extensive: - Posterior surface of the sacrum. - Posterior superior iliac spine. - Mamillary processes in the lumbar region. - All TPs in the thoracic region. - APs of C4-C7. - Insertion: Each fasciculus inserts obliquely upward to a spinous process either 3, 4 or 5 levels above the segment of origin. - Nerve supply: DPR of spinal nerves (segmental). - Action: Extension, lateral flexion and rotation of vertebral column to opposite side. (3) ROTATORES: - Located deep to the multifidus. - Extend from the sacrum to C2. - Best developed in the thoracic region. - Origin: From TPs of all lumbar, thoracic and C3-C7 vertebrae. - Insertion: Inserted into the laminae of one level above( rotatores brevis or 2 levels above( rotatores longus. - Nerve supply: DPR of spinal nerves (segmental). - Action: Extend the vertebral column and rotate it to the opposite side. MINOR DEEP BACK MUSCLES= SEGMENTAL (postural muscles) I INTERSPINALIS: - Paired on either side of interspinous ligaments, originate and insert into adjacent SPs. - Well developed in cervical and lumbar regions, not well developed in thoracic region. - Nerve supply: DPR of spinal nerves Action: extend the vertebral column. II INTERTRANSVERSARII: - Originate and insert between adjacent TPs. - Best developed in the cervical region and are paired on each side: anterior and posterior intertransversarii. - Not well developed in the thoracic region. - Well developed in lumbar region, paired: medial intertransversarii: extend between accessory processes of one lumbar vertebra to mamillary process of lumbar vertebra below. lateral intertransversarii; extend between TPs. - Nerve supply: Cervical, thoracic and lumbar lateral intertransversrii are supplied ventral primary rami of segmental spinal nerves. The medial lumbar intertransverarii are supplied by DPR of spinal nerves. - Action: Lateral flexion of vertebral column. III LEVATOR COSTARUM - Origin: From TPs of C7-T11 and run downwards and laterally to be inserted into ribs. - Insertion: - Levator costarum brevis: is inserted into the rib below (between the tubercle and angle). - Levator costarum longus (mainly in lower thoracic region): is inserted into the second rib below and is located medial to the brevis muscle originating from the same TP. - Nerve supply: Segmental from DPR. - Action: Elevate ribs (inspiration) and help laterally flex and rotate trunk to same side. SUBOCCIPITAL MUSCLES - Four small muscles, inferior to occiput in the posterior upper part of the neck. - Deepest muscles in the region; deep to trapezius, splenius capitis and semispinalis capitis. - These muscles consist of 2 recti (major and minor) and 2 obliques (superior & inferior). a. Rectus capitis posterior major: - Origin: SP of C2 (axis). - Insertion: Lateral part of inferior nuchal line. - Action: Bilateral: extension of the head. Unilateral: rotation of the head to the same side. b. Rectus capitis posterior minor: - Origin: Posterior tubercle of C1 (atlas). - Insertion: Medial part of inferior nuchal line. - Action: Extension of the head. c. Obliquus capitis inferior: - Origin: SP of C2. - Insertion: TP of C1. - Action: Rotation of the head to the same side. d. Obliquus capitis superior: - Origin: TP of C1. - Insertion: Occiput; between superior and inferior nuchal lines, lateral to semispinalis capitis. - Action: Extension and lateral flexion of the head. - Nerve supply of all suboccipital muscles: Suboccipital nerve (dorsal primary ramus of C1) : purely motor Suboccipital triangle: Boundaries: Fromed by three of the four suboccipital muscles: - Rectus capitis posterior major: superomedial. - Obliquus capitis superior: superolateral. - Obliquus capitis inferior: inferolateral. Roof: Formed by splenius capitis laterally and semispinalis capitis medially. Floor: - Posterior arch of atlas. - Posterior atlanto-occipital membrane. Contents: 1. Third (horizontal) part of vertebral artery. 2. Dorsal ramus of C1 (suboccipital nerve, purely motor) between vertebral artery and posterior arch of atlas. 3. Suboccipital plexus of veins. N.B.: The greater occipital nerve (dorsal ramus of C2) is purely sensory, it winds around the obliquus capitis inferior, pierces the semispinalis capitis and ascends to supply the back of the scalp with sensory innervation . It is involved in headache. PREVERTEBRAL MUSCLES OF NECK ANTERIOR PREVERTEBRAL MUSCLES Longus colli (longus cervicis) Longus capitis Rectus capitis anterior Rectus capitis lateralis They lie in the floor of the anterior triangle of the neck.. Longus colli (longus cervicis): long muscle of the neck Applied to the anterior surface of vertebral column extending from anterior tubercle of the atlas( body of T3 and TPs of C3-C6. It has 3 parts: Vertical part: (originates and inserts into vertebral bodies) Origin: bodies of the first three thoracic and last three cervical vertebrae. Insertion: bodies of C2-C4 vertebrae. Inferior oblique part: Origin: bodies of the first 3 thoracic vertebrae. Insertion: anterior tubercles of TPs of C5-C6 vertebrae. Superior oblique part: Origin: anterior tubercles of TPs of C3-C5 vertebrae. Insertion: anterior tubercle of atlas by a narrow tendon. Clinical consideration: torn tendon during extension injury of neck leads to its calcification, seen in the x-ray 3 weeks after injury as a radiopaque area just anterior to the atlas. - Innervation: ventral rami of C2-C6 spinal nerves. - Action: Bilateral: Flexion of the neck (3 parts). Unilateral: Rotation of neck to opposite side (inferior oblique part). Lateral flexion of neck (superior and inferior oblique parts). - Clinical consideration: Responsible for reversal or loss of cervical lordosis after extension injuries of the neck Longus capitis: long muscle of head - Anterior and slightly lateral to the upper part of longus colli - Broad and thick superiorly and narrow inferiorly - Origin: anterior tubercles of TPs of C3-C6 vertebrae. - Insertion: basilar part of occipital bone (anterior to foramen magnum) Innervation: ventral rami of C1-C4 nerves. Action: flexion of head Rectus capitis anterior: Origin: lateral mass of atlas. Insertion: occipital bone anterior to occipital condyle Innervation: ventral rami of C1 and C2. Action: flexion of the head. Rectus capitis lateralis: Origin: TP of atlas Insertion: jugular process of occipital bone. Innervation: ventral rami of C1 and C2 nerves. Action: lateral flexion of head. LATERAL PREVERTEBRAL MUSCLES: Scalenus anterior (scalenus anticus) Scalenus medius Scalenus posterior They lie in the floor of the posterior triangle of the neck Scalenus anterior: (scalenus anticus) Origin: anterior tubercles of TPs of C3-C6 vertebrae Insertion: scalene tubercle on upper surface of first rib (anterior to groove for subclavian artery and posterior to groove of subclavian vein). Innervation: ventral rami of C4-C6. Action: Acting from above: elevates first rib during forced inspiration. Acting from below: Unilateral(laterally flexes and rotates the neck to the opposite side. Bilateral( flexion of the neck. Scalenus medius: (the largest) Origin: posterior tubercles of TP of C2-C7 vertebrae Insertion: upper surface of first rib behind the groove for subclavian artery. Innervation: ventral rami of C3-C6. Action: Elevation of first rib during forced inspiration. Unilateral( lateral flexion and rotation of neck to opposite side. Bilateral( flexion of the neck. Scalenus posterior: (the smallest) Origin: posterior tubercles of TP of C4-C6 vertebrae Insertion: upper surface of second rib. Innervation: ventral rami of C6-C8. Action: Elevation of second rib during forced inspiration. Lateral flexion of neck. THORACIC OUTLET SYNDROME Thoracic inlet = Superior thoracic aperture: allows passage of anatomical structures between neck and thorax. Boundaries: T1, first pair of ribs and superior border of manubrium. Ironically, the term thoracic outlet syndrome (TOS) is frequently used to describe symptoms and signs arising from compromise of the neural and vascular structures as they pass through the region of the thoracic inlet. The symptoms of this syndrome are felt in the distal aspect of upper limb rather than the area of neurovascular compromise and they may include neurological manifestations as numbness , paresthesia, tingling and motor weakness or vascular manifestations as pallor, coldness, weak radial pulse and swelling or both. As the subclavian vessels pass through thoracic inlet, they are met with the lower roots of brachial plexus (C8 and T1) that form the lower trunk of the brachial plexus. - All the vascular and neural structures pass over the first rib (plate 29). They may be compressed in the following syndromes: (1) Scalenus anterior syndrome: spasm or hypertrophy of scalenus anterior muscle. (2) Costoclavicular syndrome: due to compression of subclavian artery and brachial plexus between the clavicle and first rib (Pancost tumor: tumor of apex of lung). (3) Cervical rib syndrome: due to compression of C8 and T1 nerve roots, lower trunk of brachial plexus and subclavian artery against the first rib( sensory, motor and vascular manifestations along the ulnar side of the forearm. The cervical rib develops from the costal element of TP of C7. It may be a very small projection of the anterior tubercle of C7 TP or may be a complete rib that attaches to manubrium or the first thoracic rib or incomplete and a bridge of fibrous tissue connects the tip of the cervical rib to either manubrium or the first rib (plate 181). (4) Hyperabduction syndrome: due to compression of axillary artery and vein and the cords of brachial plexus by pectoralis minor muscle as it inserts into the coracoid process during abduction and lateral rotation of the arm (painting the ceiling). Adson?s maneuver (an orthopedic test): - This test is one of the most common methods of testing for thoracic outlet syndrome. - The examiner locates the radial pulse. - The patient?s head is rotated to face the test shoulder. - The patient then extends the head while the examiner laterally rotates and extends the patient?s shoulder. - The patient is instructed to take a deep breath and hold it. - A disappearance or weakness of radial pulse indicates a positive test. SPINAL CORD - The spinal cord, meninges and related structures are located in the vertebral canal (neural canal, spinal canal) formed by successive vertebral foramina. - The spinal cord is the major reflex center and conduction pathway between the body and the brain. - It is protected by the: vertebral bodies and arches. their associated ligaments and muscles spinal meninges CSF - The spinal cord is a cylindrical structure that begins as a continuation of the medulla oblongata at the foramen magnum and ends at L2 vertebral level (so it occupies the upper 2/3 of vertebral canal). It is about 42-45 cm long, 1 cm in diameter and 30 gm in weight. Its tapering inferior end is known as the conus medullaris. - In the embryo, the spinal cord occupies the full length of the vertebral canal, and thus the spinal cord segment lies approximately at the vertebral level of the same number and the spinal nerves exit their corresponding IVFs almost horizontally. - During fetal life, the vertebral column grows faster than the spinal cord. - Thus, there is progressive obliquity of spinal nerve roots. Because of increasing distance between spinal cord segments and their corresponding vertebrae, the length of the roots increases progressively from above downward. They descend till they exit at their corresponding IVF. They look like horse?s tail( cauda equina. External features of the spinal cord: (plate 169) - The dorsal (posterior) surface of the spinal cord shows: Midline dorsal median sulcus. Right and left dorsal intermediate sulci Right and left dorsal lateral sulci (attachment of dorsal rootlets of spinal nerves) - The ventral (anterior) surface of the spinal cord shows: Midline ventral median fissure Right and left ventral lateral sulci (attachment of ventral rootlets of spinal nerves) - The outward attachment of paired dorsal rootlets and paired ventral rootlets defines one spinal cord segment. Fusion between ventral and dorsal roots( spinal nerve. - One pair of spinal nerves is therefore associated with one spinal cord segment; thus there are 31 spinal cord segments which are not located always at the same level of their corresponding vertebrae (plate 154). - The spinal cord is enlarged in two regions for innervation of the limbs: (1) Cervical enlargement: C5-T1( corresponds to almost same vertebral levels): most of the ventral rami of its spinal nerves form the brachial plexus that innervates the upper limbs. (2) Lumbar enlargement: L1-S4 (corresponds to vertebral levels T9-T12), its ventral rami give lumbar and sacral plexuses that mainly innervate the lower limbs. Structure of spinal nerves - 31 pairs of spinal nerves are attached to the spinal cord (plate 160): 8 cervical (the upper 7 cervical nerves emerge above their corresponding cervical vertebrae; C8 exits below C7 vertebra), 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal (each exits below the respective vertebra). - Each spinal nerve is formed of a ventral root and a dorsal root. Each root is formed of several rootlets that emerge from the ventral and dorsal surfaces of the spinal cord respectively. - The 2 roots unite to form the spinal nerve that exits through the IVF of the corresponding segment of the spinal cord. - The dorsal roots of spinal nerves contain sensory fibers (afferent fibers from the skin, deep tissues and viscera). Each dorsal root receives sensory afferent fibers from an area of the skin called dermatome - The cell bodies of axons making the dorsal roots are outside the spinal cord, in the dorsal root ganglia (spinal ganglia) that are located in the IVFs. - The ventral roots of spinal nerves contain efferent (motor) fibers to skeletal muscles and many contain preganglionic sympathetic autonomic fibers. - The cell bodies of axons making ventral roots are in the ventral gray horns of the spinal cord. - The first cervical nerve (C1) has no dorsal root( purely motor (supplies muscles of suboccipital region and is called suboccipital nerve). - The coccygeal nerve may be absent. - Each spinal nerve divides into two branches:1. dorsal primary ramus and 2. ventral primary ramus (both rami are mixed: contain sensory and motor fibers). - The dorsal primary rami: supply the skin and deep muscles of the back. - The ventral primary rami: supply the limbs and the rest of the trunk through 5 plexuses (cervical, brachial, lumbar, sacral and coccygeal plexuses). The ventral primary rami of thoracic spinal nerves form 11 intercostal nerves and subcostal nerve: T12 - Two other branches of spinal nerves: 3. recurrent meningeal nerves: supply meninges and IVDs 4. white rami communicans: to sympathetic ganglia. TYPES OF FIBERS IN SPINAL NERVES (1) General somatic afferent (GSA) fibers: sensory Transmit pain, temperature, touch and proprioception from the body to CNS. (2) General somatic efferent (GSE) fibers: motor Carry motor impulses to skeletal muscles of the body (3) General visceral afferent (GVA) fibers: sensory Carry sensory impulses from visceral organs to CNS. (4) General visceral efferent (GVE) fibers: motor Transmit motor impulses to smooth muscles, cardiac muscles and glands. SPINAL MENINGES (1) Dura Mater: (rough mother) - A tough fibrous elastic tissue. - Outermost covering membrane - Outside it( extradural or epidural space that contains: a. adipose tissue b. internal vertebral venous plexuses (anterior and posterior) - Boundaries of epidural space: Superiorly: foramen magnum Inferiorly: sacrococcygeal ligament covering sacral hiatus Anteriorly: vertebral bodies, IVDs and PLL Posteriorly: laminae and ligamentum flavum Laterally: Pedicles and IVFs The dura mater forms a dural sac within the vertebral canal that ends at S2. - The dural sac attaches to the margins of the foramen magnum where it is continuous with the meningeal layer of cranial dura mater. The dura mater is anchored inferiorly to the coccyx by the filum terminale externum. - The spinal dura mater extends along the dorsal and ventral roots and spinal ganglia to form dural root sleeves. (2) Arachnoid Mater: (spider web) - A delicate, avascular membrane that lines the dural sac and is continuous with the cranial arachnoid mater. - It is separated from the dura mater by the subdural space (potential space). - It also covers the spinal nerve roots and spinal ganglia. - It is separated from the deeper pia mater by the subarachnoid space which contains CSF and blood vessels. It is connected to pia mater by web-like trabeculae. (3) Pia Mater: (tender mother) - Innermost layer of the meninges. - A thin vascular delicate membrane that adheres closely to the surface of the spinal cord. It also surrounds the nerve roots to IVFs. - It is continuous with the pia mater of the brain. It contains the plexus of small blood vessels of the spinal cord. - The pia mater of spinal cord has two specializations that anchor the spinal cord in place: (1) Filum terminale: A slender filament of pia mater that extends for about 20 cm from the tip of the conus medullaris to the dorsum of the coccyx. Inside the dural sac, it is known as the filum terminale internum.At the level of S2, it picks 2 additional layers from the dura and arachnoid mater( filum terminale externum /coccygeal ligament (2) Denticulate ligament A serrated ribbon of pia mater that attaches to the dura mater at about 21 points on each side between the dorsal and ventral roots of spinal nerves. Subarachnoid space - Lies between the arachnoid mater and pia mater and is filled with CSF. It also contains the large arteries and veins that vascularize the spinal cord. - This space is large inferior to the conus medullaris forming the lumbar cistern which extends from L2 vertebra to S2 segment. It contains the cauda equina and filum terminale internum that float in CSF, thus are not damaged by lumbar puncture needle. - The CSF is formed by the choroid plexuses in the lateral, third and fourth ventricles of the brain. It is drained through arachnoid villi and granulations into venous dural sinuses to the general circulation. It acts as a shock absorber as well as diffusion medium for dissolved gases, nutrients, chemical massangers and waste products. - The totals amount of CSF is 80-150 ml and it replaces itself 4-5 times daily. Clinical considerations: Lumbar puncture = spinal tap: - It is done below L2 vertebra since the spinal cord ends at this level. The spinous processes are almost horizontal at that level. - A long needle is inserted in the midline between L3-L4 or L4-L5 vertebrae into the lumbar cistern and 5-15 ml of CSF are removed. It is done for diagnostic purposes. - Lumbar puncture may also be done for diagnostic imaging (myelography) and anesthetic purposes( spinal anesthesia (spinal block). Headache is a common complaint following spinal block, it may result from leakage of CSF through the opening made in the dura and arachnoid by the needle. - The needle penetrates the skin, fascia, back muscles, supraspinous and interspinous ligaments and ligamentum flava, epidural space, dura mater, subdural space and arachnoid mater. Epidural block/Epidural anaesthesia: - An anesthetic agent is injected into the epidural space using the same position as for lumbar puncture or through the sacral hiatus. - The anesthetic has a direct effect on the spinal nerve roots of the cauda equina as they exit the dural sac. - The effect of an epidural block usually lasts for 10-20 min. - The patient remains awake. It is commonly used to prevent pain during childbirth. The birth canal is anesthetized (innervated by S2-S4 nerves: pudendal nerve) while the uterus is not: so the mother is aware of her uterine contractions. Meningitis: is inflammation of the pia mater and arachnoid mater. It could be viral or bacterial. Clinical picture: fever, headache and neck stiffness. Valsalva?s maneuver: - The examiner asks the seated patient to take a deep breath and hold it while bearing down, as if moving the bowels. - A positive test is indicated by increased pain, which may be caused by increased intrathecal pressure. This may be due to a space-occupying lesion such as herniated disc, tumor or osteophytes. INTERNAL STRUCTURE OF THE SPINAL CORD Cross section of the spinal cord shows: A butterfly or H-shaped central area of gray matter. A peripheral area of white matter formed of myelinated axons. Gray matter: - Each half of the H-shaped gray matter consists of a thin dorsal horn, a thick ventral horn and an intermediate area. In spinal cord segments T1-L2, the intermediate zone includes a lateral horn. - The crossbar of the H-shaped gray matter is formed of commissural neurons and surround the central canal which contains CSF. - The gray matter is formed of neurons (arranged in groups of cells known as nuclei), neuroglia and capillaries. - The dorsal horn contains sensory neurons which receive sensory input from the dorsal roots carrying different types of sensations (somatic and visceral). - The lateral horns of (T1-L2) include neurons of sympathetic nervous system innervating smooth muscles, cardiac muscle, sweat glands and adrenal medulla. - The ventral horns contain motor neurons from which axons leave through the ventral roots carrying motor output to skeletal muscles. Those neurons are known as anterior horn cells (AHC). White matter: - Includes myelinated axons, neuroglia and blood vessels. - Myelin is formed by Schwann cells in peripheral nerves and oligodendroglia cells in CNS - White matter is divided into 3 major areas called columns or funiculi. - Dorsal column is located between dorsal horns. Lateral column is located between each dorsal and ventral horn. ventral column is located between ventral horns. - Each column is formed of tracts or fasciculi that contain ascending and descending axons. - The dorsal column contains ascending sensory tracts mainly. The ventral column contains descending motor tracts mainly and the lateral column contains both ascending and descending tracts Clinical considerations: Spinal cord injuries: - Accidents( transection of the cord( paraplegia or quadriplegia depending on the level of the lesion. -Aging( osteoarthritis( osteophytes (bone spurs) which may compress nerve roots in IVFs( pain. Regional characteristics of the spinal cord in cross section: - Cervical region: i) large and oval-shaped. ii) the amount of white matter is greater than any other region. iii) the ventral horn of gray matter is large (large number of neurons to innervate upper limb muscles). - Thoracic region: i) small amount of gray matter relative to white matter. ii) thin dorsal and ventral horns iii) presence of a lateral horn. - Lumbar region: i) round appearance. ii) dorsal and ventral horns are very large. iii) relatively less white matter than cervical region. - Sacral region: i) predominance of gray matter over white matter. ii) smallest cross section of the spinal cord. VASCULATURE OF THE SPINAL CORD Arterial supply (1) Vertebral artery branches: Spinal branches arise from the fourth part of vertebral arteries within the cranial cavity and form 3 longitudinal arteries: a. One anterior spinal artery: runs in the anterior median fissure of the spinal cord. Two posterior spinal arteries: run in the posterolateral sulci of the spinal cord. (2) Segmental arteries: which are branches of deep cervical, ascending cervical posterior intercostal, lumbar and lateral sacral arteries. They accompany the spinal nerves through IVFs, and divide into: a. Radicular arteries: anterior and posterior radicular arteries which supply the ventral and dorsal roots of spinal nerves respectively and end there. b. Medullary arteries: reach the spinal cord along nerve roots and may be: i. anterior segmental medullary arteries: anastomose with the anterior spinal arteries. ii. posterior segmental medullary arteries: anastomose with the posterior spinal arteries. The great anterior segmental medullary artery of Adamkiewicz at the level of T 9 on the left side of 65% of persons reinforces the circulation to lower 2/3 of spinal cord (lumbosacral enlargement). It is also known as arteria radicularis magna. VENOUS DRAINAGE - There are usually 3 anterior and 3 posterior spinal veins which are arranged longitudinally along the spinal cord. - They drain the spinal cord into the medullary and radicular veins and join the internal vertebral venous plexus (anterior and posterior): IVVP, located in the epidural space. - This plexus drains into intervertebral segmental veins( systemic circulation. The IVVP, also communicates with the external vertebral venous plexus (anterior and posterior) located on the external surface of vertebrae through basivertebral veins. - The internal vertebral venous plexus communicates superiorly with the cranial venous dural sinuses and inferiorly with the pelvic veins and in the thoracic and lumbar regions with the azygos vein and IVC. - The vertebral venous plexuses are valveless. Clinical considerations: (1) The internal vertebral venous plexus is the route of early metastasis of carcinoma from various organs, e.g. the lung, breast and prostate to vertebrae and CNS. (2) Ischemia of the spinal cord: due to fractures, ruptured aortic aneurysm, or occlusion of the aorta by clamping during surgery may lead to anesthesia, muscular weakness and paralysis. BOUNDARIES OF IVFs Superiorly: inferior vertebral notch. Inferiorly : superior vertebral notch. Anteriorly: vertebral bodies and IVDs. Posteriorly: ligamentum flavum and Z joints. CONTENTS OF IVFs: Spinal nerve roots (dorsal and ventral roots). Dorsal root ganglia. Segmental arteries and veins. Clinical application: Narrowing of IVF by bone spurs or hypertrophy of ligamentum flavum causes pain due to nerve impingement. IVFs become larger in spinal flexion and narrower in spinal extension IVFs are smaller in the cervical region CERVICAL PLEXUS - Formed by ventral rami of upper 4 cervical nerves. - Lies opposite the upper 4 cervical vertebrae deep to SCM. - Has 4 cutaneous branches. - Has many muscular branches mainly to diaphragm (phrenic) and infrahyoid muscles (ansa cervicalis). Cutaneous Branches of Cervical Plexus: Emerge at the middle of posterior border SCM (Erb?s point). Lesser occipital (C2): supplies skin of scalp posterior and superior to the auricle and upper half of medial surface of the auricle. Great auricular (C2 and C3): ascends diagonally across SCM (parallel and superior to external jugular vein) and supplies the skin over: - parotid gland, - angle of mandible, - mastoid process, - lower ½ of auricle (lateral and medial aspects) Transverse cervical (C2 and C3): supplies skin of the front and side of neck. Supraclavicular (C3 and C4): - medial, intermediate and lateral - descend over the clavicle, supply the skin of shoulder and upper part of anterior chest wall (about one hand?s breadth below the clavicle). Motor Branches Of Cervical Plexus: Phrenic nerve (C3, C4, C5): - Contains motor, sensory and sympathetic fibers. - The only motor supply to diaphragm. - Descends anterior to scalenus anterior muscle. - Clinical application: severance of phrenic nerve ( paralysis of hemidiaphragm. (2) Ansa cervicalis: (ansa= loop) - Lies in front of or embeded in or within the carotid sheath. - Arises from 3 cervical nerves and supplies 3 infrahyoid muscles. - Formed by union of two descending roots: Superior root: from C1 that accompanies hypoglossal nerve (CN XII) and thus it is called descendens hypoglossi. B) Inferior root; from C2 and C3. - Supplies: sternohyoid, sternothyroid and omohyoid muscles. Other branches are for prevertebral muscles, sternocleidomastoid and trapezius (proprioceptive) and levator scapulae. C1 gives muscular branches to: thyrohyoid and geniohyoid muscles. BRACHIAL PLEXUS - The main nerve supply to upper limbs. - Formed of ventral primary rami of C5-T1 spinal nerves. - It courses through the root of the neck and axilla before reaching the arm. - It consists of roots, trunks, divisions, cords and branches. I. ROOTS: - Are the ventral primary rami of C5-T1 - Located between scalenus anterior and scalenus medius muscles. - Each root supplies a dermatome. - Branches from the roots: 1. Dorsal scapular nerve (C5): innervates levator scapulae, rhomboid minor and rhomboid major muscles( retraction of scapula (adduction). 2. Long thoracic nerve (C5,6,7): innervates serratus anterior muscle( protraction of scapula (boxer?s muscle).Lesion of this nerve causes winged scapula. II. TRUNKS: Formed by joining of roots in the neck. a. Upper trunk: is formed by joining of C5 and C6 roots. It gives rise to 2 nerves: 1. Suprascapular nerve (C5,6)( supraspinatus and infraspinatus muscles. muscles (main lateral rotators of the arm). 2. Subclavius nerve (C5,6). b. Middle trunk: is the continuation of C7 root. c. Lower trunk: is formed by union of C8 and T1 roots. III. DIVISIONS: - Are formed by splitting of the trunks into anterior and posterior divisions deep to the clavicle. - The posterior divisions of three trunks join ( posterior cord. - The anterior divisions of the upper and middle trunks( lateral cord. - The anterior division of the lower trunk( medial cord. IV. CORDS and V. Terminal Branches: a. Lateral cord gives 3 branches: Lateral pectoral nerve( supplies pectoralis major muscle. Musculocutaneous nerve (C5,6,7) ( motor: flexion of forearm and sensory for the lateral side of forearm. Lateral root of median nerve. b. Medial cord gives 5 branches: Medial pectoral nerve (C8-T1) ( supplies pectoralis minor and major muscles. Medial root of the median nerve. Ulnar nerve (C8-T1) ( abduction and adduction of the fingers. Medial cutaneous nerve of forearm (C8-T1): carries sensation from medial side of forearm. Medial cutaneous nerve of arm(T1) ( carries sensation from medial side of arm. Median nerve (C6,7,8): pinching between thumb and fingers. c. Posterior cord (C5-T1): gives 5 branches (ULTRA): Upper subscapular (C5,6) ( subscapularis muscle( adduction and medial rotation of arm. Lower subscapular (5,6) ( teres major( adduction and medial rotation of arm. Thoracodorsal nerve (6,7,8): latissmus dorsi muscle (swimmer?s muscle) ( medial rotation, adduction and extension of arm (MAE). Radial nerve (C5-T1) ( innervates all extensor muscles of upper limb:lesion( wrist drop. Axillary nerve (C5,6) ( teres minor (lateral rotation) and deltoid (abduction). LUMBAR PLEXUS Arises from the ventral primary rami of L1-L4 spinal nerves within the substance of the psoas major muscle. - It shares in the innervation of the abdominal wall and lower limbs. - It gives six branches (4 small and 2 main). Iliohypogastric nerve (L1): Motor and sensory to lower abdomen. Ilioinguinal nerve (L1): Motor: lower abdominal muscles. Sensory: inguinal region. Lateral cutaneous nerve of thigh (L2, 3): Sensory (only): skin innervation of lateral upper anterior thigh. Genitofemoral nerve (L1,2): pierces psoas major anteriorly and divides into: Genital branch: motor to cremaster muscle in men only. Femoral branch: sensory to skin of medial upper anterior thigh. Femoral nerve (L2,3,4) Motor: flexes the thigh and extends the knee. Sensory: skin of anterior thigh and through its saphenous branch, it supplies the medial side of knee, leg and foot . (6) Obturator nerve (L2,3,4) Motor: adduction of thigh. Sensory: skin of medial side of thigh. SACRAL PLEXUS - It is formed by the ventral primary rami of L4-S4 spinal nerves within the pelvis, anterior to piriformis muscle. - It supplies the pelvis, perineum, gluteal region and lower limbs. - The major branches are: Superior gluteal nerve (L4, 5, S1): Motor: gluteus medius, gluteus minimus and tensor fascia lata( abduction of thigh. Inferior gluteal nerve (L5,S1,2): Motor: gluteus maximus(main extensor of thigh. Posterior cutaneous nerve of thigh (S1,2, 3): Sensory: back of thigh. Pudendal nerve (S2,3,4): Motor: muscles of perineum, external anal sphincter and external urethral sphincter. Sensory: posterior 2/3 of genitalia. Sciatic nerve (L4, 5& S1,2,3) The largest nerve in the body. It divides into two terminal branches: a. Tibial nerve: Motor to: posterior thigh ( extension of thigh, and to posterior leg ( plantar flexion of ankle (walking on toes). Sensory: sole of foot and heel by medial/lateral plantar and calcanean nerves. b. Common peroneal (fibular) nerve: It divides into: i. Superficial peroneal (fibular): Motor: lateral leg muscles( peroneus longus and brevis( Eversion of foot. Sensory: lateral ½ leg and most of dorsum of foot. ii. Deep peroneal (fibular): Motor: anterior leg muscles( dorsiflexion of ankle: walking on heels (damage causes foot drop). Sensory: dorsal part of foot between big toe and 2nd toe (first interdigital space: L5). Sural nerve: is formed by lateral sural nerve (from common peroneal) and medial sural nerve (from tibial). It is sensory to posterior leg and lateral foot. THE AUTONOMIC NERVOUS SYSTEM The nervous system is formed of: CENTRAL NERVOUS SYSTEM (CNS): Brain: located in the cranial cavity Spinal cord: located in vertebral canal. PERIPHERAL NERVOUS SYSTEM (PNS): Composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves and associated ganglia. Functionally it is divided into: Somatic Nervous System: sensory and motor innervation of somatic structures as skin, muscles, tendons, joints??.. etc. through cranial and spinal nerves. Visceral Nervous System: sensory and motor innervation of involuntary structures like heart, smooth muscles (in internal organs and blood vessels) and glands. - THE MOTOR PART OF THE VISCERAL NERVOUS SYSTEM IS KNOWN AS THE AUTONOMIC NERVOUS SYSTEM (ANS). - ANS is divided into: sympathetic and parasympathetic. - The motor supply to visceral structures (heart, intestine) differs from the motor supply to somatic (striated; skeletal) muscles in two major points: (1) Most of the visceral structures have two motor nerve supply; one sympathetic and one parasympathetic. One of these nerves acts as an excitor, while the other acts as an inhibitor. (2) Each of the two motor nerves (sympathetic and parasympathetic) is formed of a chain of 2 NEURONS: a. The body of the first neuron is found in CNS and its axon is called a preganglionic fiber. b. The body of the second neuron is found in ganglia in the PNS (either in sympathetic or in parasympathetic ganglia) and its axon is called postganglionic fiber. Striated (skeletal) muscles Visceral structures (Smooth muscles, heart & glands) 1. Receive ONE motor nerve supply only called somatic nerve Receive TWO motor nerve supply: one sympathetic & one parasympathetic 2. The motor nerve is formed of ONE neuron only; its cell body lies in CNS Each of the TWO motor supply is a chain of TWO neurons: preganglionic in(CNS) and ganglionic in (PNS) The sympathetic and parasympathetic systems are antagonistic. The sympathetic nervous system is the system of defense against any harm to the body, fight or flight or fright. - The effect of sympathetic stimulation is generalized. - The generalized activity of sympathetic system is increased by secretion of chemical transmitter adrenaline (epinephrine) and noradrenaline (norepinephrine) from the medulla of adrenal gland. - The activity of the parasympathetic system is localized and regulates the visceral activity during rest and reserves body resources. - The sympathetic nervous system supplies: a. The arterioles, sweat glands and arrector pili muscles of the skin. b. Blood vessels of the limbs. c. Deep viscera. - The parasympathetic system supplies the deep viscera ONLY; it does not supply the skin nor the limbs - The ganglia of the sympathetic system lie in two different locations: a. Sympathetic chain (paravertebral) ganglia: which lie on either side of the vertebral column and extend from the atlas (C1) to the coccyx where the two chains fuse and form a single ganglion called the ganglion impar. b. Collateral (prevertebral) ganglia: around large arteries which arise from the abdominal aorta e.g.: celiac, superior and inferior mesenteric ganglia. - The ganglia of the parasympathetic system are present ON or IN the walls of the organs( terminal ganglia. Accordingly preganglionic parasympathetic fibers are long and postganglionic fibers are short. On the other hand, the preganglionic sympathetic fibers are short and the postganglionic fibers are long. SYMPATHETIC NERVOUS SYSTEM (THORACOLUMBAR) - The cells bodies of the preganglionic neurons lie in the lateral horns of all thoracic and L1 and L2 segments of the spinal cord. - The preganglionic fibers leave the spinal cord through the ventral roots of spinal nerves and leave the ventral roots as white rami communicans (14) to join the sympathetic chain. - A preganglionic fiber can do one of four things when it enters the sympathetic chain: (1) It may synapse with a postganglionic neuron in paravertebral ganglia of the same level. (2) It may pass up or down the chain to synapse with a postganglionic neuron in paravertebral ganglia several levels away. ( Postganglionic fibers join spinal nerves (as gray rami Communicans: 31) to supply skin or form sympathetic nerves or plexuses around blood vessels to supply visceral organs in head, neck and thorax. (3) It may NOT synapse in the sympathetic chain (paravertebral ganglia) at all and continue as preganglionic fiber to form the thoracic and lumbar splanchnic nerves that synapse with postganglionic neuron in prevertebral ganglia and then supply abdominopelvic viscera. (4) It may not synapse in paravertebral or prevertebral ganglia but instead pass through them to synapse with cells in the adrenal medulla. - Sympathetic preganglionic neurons are cholinergic (acetyl choline is the neurotransmitter). - Sympathetic postganglionic neurons are adrenergic (adrenalin is the neurotransmitter) except in eccrine/merocrine sweat glands, the neurotransmitter is acetyl choline. PARASYMPATHETIC NERVOUS SYSTEM (CRANIOSACRAL) - The parasympathetic system arises from: a. Cranial nerve nuclei number 3, 7, 9 and 10: CN III (oculomotor)( pupillaty constriction. CN VII (facial) ( lacrimation and salivation. CN IX (glossopharyngeal) ( salivation CN X (vagus): - slows heart rate. - bronchoconstriction. - motor to bowel: movement and secretion b. Sacral part of spinal cord: From lateral part of gray mater of S2, 3 and 4 segments of the cord (pelvic splanchnic nerves, nervus erigentes): Increase smooth muscle activity and inhibit sphincters (emptying) of: - bladder. - rectum. Controls genital organs except that ejaculation in males is controlled by sympathetic system (erection is controlled by parasympathetic system). Both preganglionic and postganglionic neurons are cholinergic because the neurotransmitter acetyl choline is secreted at the terminals. ENTERIC DIVISION OF ANS: - Consists of enteric ganglia and plexuses of GI tract including myenteric (Auerbach?s) and submucosal (Meissner?s) plexuses. - Plays an important role in the control of GIT motility and secretion. THE VISERAL AFFERENTS (GVA): Afferent innervation from the viscera is not considered part of the ANS, because, the ANS by definition is a visceral motor system. Afferent pathway: Afferent pain fibers from the viscera pass retrograde along either thoracic or lumbar splanchnic nerves to reach sympathetic chain, then through white rami communicans to dorsal root ganglia of the spinal nerves to the spinal cord. From the lower pelvic organs, afferent pain fibers pass retrograde along the pelvic splanchnic nerves to S2-4 segments of the spinal cord. Referred pain: - It is a painful sensation in a region of the body that is not the source of pain. - Pain fibers from the viscera reach the spinal cord. - Pain is referred to the somatic dermatome of the spinal level that received the visceral afferent nerve. - The reason that visceral pain is perceived as originating from dermatomes is not understood. It could be explained by the fact that the brain cannot distinguish between the two sites of pain (somatic and visceral) because they converge to the same dorsal root ganglion, and the pain is referred to the most superficial structures. This may occur because the number of receptors is much greater in superficial structures and the brain is more ?accustomed? to dealing with superficial stimuli. Referred pain is clinically useful in diagnosing the actual cause of painful stimuli. Heart attack victims often feel cutaneous pain radiating from the left shoulder down the arm. Clinical considerations: ANS regulates blood pressure and heart rate: - Orthostatic hypotension: is a drop in blood pressure that occurs when a person stands suddenly from a sitting or lying down position. It is due to decreased sympathetic activity to peripheral arterioles( dilation of the blood vessels of the limbs( decreased venous return to the heart( decreased blood flow to the brain( fainting due to lack of oxygen. Carotid sinus massage: stimulates baroreceptors which send afferent impulses to CNS through CN IX. Efferent impulses travel through the vagus and slows the heart rate. Either afferent or efferent lesions abolishes this response. DEVELOPMENT OF VERTEBRAL COLUMN There are 3 primary structures to consider in development of human vertebral column: The notochord. The mesodermal somites. The sclerotomes. Notochord: - It is also referred to as the chorda dorsalis. - It is one of the first recognizable structures in the embryo, appearing around day 18. - It is derived from embryonic mesoderm in the third week and extends from the future sphenoid bone to the coccyx region. - It is a primitive supporting structure which represents the beginning of the axial skeleton in all vertebrates. In man it is a temporary structure to be replaced by the vertebral column. It persists in the adult as the nucleus pulposus of the IVD. - The entire development of the vertebral column takes place around the notochord and neural tube. Paraxial Mesoderm: It forms a segmented series of tissue blocks on each side of the neural tube, known as somitomeres in the head region and somites from the occipital region caudally. Mesodermal somites differentiate into ventromedial part; the sclerotome and a dorsolateral part; the dermomyotome, which differentiates into myotomes( give rise to skeletal muscles) and dermotomes (give rise to dermis and subcutaneous connective tissue). The total number of somites in the human embryo is 38 to 39 pairs: 1 occiput 7 cervicals 12 thoracics 5 lumbars 5 sacrals 8-9 coccygeal (a few that develop in the tail soon disappear). Sclerotomes: at the end of the fourth week of embryonic life, sclerotome cells become polymorphous and form a loosely woven tissue, the mesenchyme or embryonic connective tissue that contains undifferentiated mesenchymal cells. The cells differentiate into fibroblasts, chondroblasts and osteoblasts (bone-forming cells). Each of these three types of cells gives rise to a stage in the development of the vertebral column. VERTEBRAL DEVELOPMENT The vertebral column develops in three stages: Mesodermal Chondrification Ossification Mesodermal stage: During the fourth week of development, cells of the sclerotomes shift their position to surround the neural tube and the notochord. The onset of mesodermal stage is marked by mesenchymal condensation of the sclerotomes. A fissure separates the sclerotomes into 2 halves: the lower half of one sclerotome joins the upper half of the sclerotome below: vertebra is intersegmental in origin. From each pair of recombined sclerotomes, a rapid growth of mesenchyme takes place in 3 directions: ( ventrally to surround the notochord to form the vertebral body. ( dorsally around the neural tube to form the vertebral arch. ( laterally to form the transverse processes and costal elements. The original fissure becomes filled with mesenchyme and forms the anulus fibrosus part of IVDs. - Although the notochord regresses entirely in the region of vertebral bodies, it persists and enlarges in the region of the intervertebral disc. Here it contributes to the nucleus pulposus, which is later surrounded by concentric layers of collagen fibers and chondrocytes of the anulus fibrosus. Chondrification stage: - Around the sixth week, centers of chondrification appear and cartilage begins to replace the mesoderm. - Chondrification appears first in the cervical vertebrae and shortly thereafter in the remaining. - It starts in six centers: 2 in the vertebral body one in each vertebral arch one in each T.P. - Cartilagenous stage proceeds until the entire membranous vertebral column has been changed into cartilage. Ossification stage: - It begins in the human embryo during the tenth week through appearance of ossification centers and continues after birth. - Thus, centers of ossification are divided into primary and secondary: Primary begins during fetal life, before birth. Secondary begins after birth. - Ossification first begins in the lower thoracic or upper lumbar and rapidly progresses to the cervical region. Sacral and coccygeal regions are the last to show ossification. Centers of Ossification: Atlas: - It is usually ossified from three centers. - Two primary centers, one on each lateral mass, appear during the seventh week. The third, a secondary center, is on the anterior arch and appears around birth. A failure of fusion in the center of the posterior arch is a common anomaly of C1 and is termed agenesis of the atlas and may be associated with other anomalies of the neural tube (Arnold-Chiari malformation) Axis: seven centers of ossification; 5 primary (3 as any typical vertebrae and 2 for the dens) and 2 secondary centers (one for the dens) What do you know about Os odontoideum? What do you know about persistent ossiculum terminale? Cervical vertebrae 3-6 and all thoracic vertebrae: - Three primary centers (one in the centrum and one in each half of the neural arch/vertebral arch). - Five secondary centers. - Primary ossification is usually completed by three to six years after birth. - Secondary centers begin to appear during the 17th year. Fusion with the remainning already ossified vertebrae is completed by the 25th year. Seventh Cervical Vertebra: - Has 3 typical ossification centers (3 primary; one in the body and one in each half of the vertebral arch). - Has 2 additional primary centers for the costal processes and may develop into cervical ribs Lumbar vertebrae: Ossify in the same manner as do the cervical vertebrae (3-6) and all the thoracic vertebrae, with one exception: lumbar vertebrae exhibit two additional primary centers of ossification. From these centers develop the mamillary processes. Thus, lumbar vertebrae have 10 centers of ossification: 5 primary and 5 secondary. Sacrum: - It is considered to be one bone or a false vertebra. - It has 37 primary centers of ossification and 12 secondary centers. - By age of 25 the sacrum has completely ossified as a single bone. Coccyx: - It is considered to be one bone or false vertebra. - The coccyx has four secondary centers; one for each segment. - By 25-30 years of age, ossification is complete. - It is not uncommon to find the coccyx fused with the apex of sacrum. CONGENITAL ANOMALIES: (1) Hemivertebrae: It is fairly common to have two successive vertebrae fuse asymmetrically or have a half vertebra missing ( wedged-vertebra; a cause of scoliosis (lateral curving of the spine). (2) Klippel-Feil Anomaly: These patients have fewer than normal cervical vertebrae, some of them are fused or are abnormal in shape. (3) Neural tube defects (NTDs): - Most defects of the spinal cord result from abnormal closure of the neural folds in the third or fourth week of development. - The resulting abnormalities are known as NTDs and also involve the meninges, vertebrae, muscles and skin. Spina bifida occulta: - It is the result of incomplete fusion or non-union of the vertebral arches. - Usually involves only the bony vertebral arches, leaving the spinal cord intact. In these cases the bony defect is covered by skin marked by a patch of hair. There are no neurological deficits. It is present in about 10% of population. Spina bifida cystica: two types Meningocele: the meninges only bulge dorsally. Meningomyelocele: the meninges and neural tube bulge dorsally. There are neurological defects. - Occurs in 1/1000 births. Rachischisis (myeloschisis): congenital fissure of the vertebral column. A more severe abnormality in which the neural folds fails to elevate and remain as a flattened mass of neural tissue and the vertebral arches fail to form and neural tissue is thus exposed. Neurological defects occur. NEURAL TUBE DEFECTS MAY BE PREVENTED BY PROVIDING MOTHERS WITH FOLIC ACID EARLY DURING PREGNANCY. PAGE PAGE 63 Dr. Isis zaki
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