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Brain and Cranial Nerves Chapter 13 FOCUS ON LOCATIONS AND FUNCTIONS! CNS consists of the brain and spinal cord Cephalization Evolutionary development of the rostral (anterior) portion of the CNS Increased number of neurons in the head Highest level is reached in the human brain Brain and Cranial Nerves Brain Part of CNS contained in cranial cavity Control center for many of body?s functions Much like a complex computer but more Parts of the brain Brainstem: connects spinal cord to brain; integration of reflexes necessary for survival Cerebellum: involved in control of locomotion, balance, posture Diencephalon: thalamus, subthalamus, epithalamus, hypothalamus Cerebrum: conscious thought, control Cranial nerves: part of PNS arise directly from brain. Two pairs arise from cerebrum; ten pairs arise from brainstem Sagittal Section of Brain Brain Stem Three regions Medulla oblongata Pons Midbrain Frontal lobe Olfactory bulb (synapse point of cranial nerve I) Optic chiasma Optic nerve (II) Optic tract Mammillary body Pons Medulla oblongata Cerebellum Temporal lobe Spinal cord Midbrain Brain Stem Brain Stem Similar structure to spinal cord but contains embedded nuclei Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Associated with 10 of the 12 pairs of cranial nerves Brain Stem: Medulla Oblongata Most inferior part Continuous with spinal cord; has both ascending and descending nerve tracts Discrete nuclei in internal gray matter Regulates: heart rate, blood vessel diameter, respiration, swallowing, vomiting, hiccupping, coughing, and sneezing Pyramids: descending nerve tracts on the anterior surface. Inferiorly fibers decussate; thus each half of the brain controls the opposite half of the body Olives: rounded; protrude from anterior surface. Nuclei within help regulate balance, coordination, modulation of sound from inner ear Nuclei of cranial nerves V, IX-XII Brain Stem: Pons Superior to the medulla oblongata Fiber tracts: ascending and descending Nuclei Pontine: anterior portion, relay between cerebrum and cerebellum For cranial nerves V-IX: posterior portion Sleep center Respiratory center coordinates with center in medulla Brain Stem: Midbrain Also called mesencephalon Small and superior to pons Nuclei Of cranial nerves III-V Tectum: four nuclei that form mounds on dorsal surface of midbrain. Corpora quadrigemina Each separate part is a colliculus Two superior colliculi involved in visual reflexes; receive information from inferior colliculi, eyes, skin, cerebrum Two inferior colliculi involved in hearing Red nuclei of tegmentum: aid in unconscious regulation and coordination of motor activities Substantia nigra: pigmented with melanin; interconnected with basal nuclei of the cerebrum (muscle tone/coordinating movements) Tracts Tegmentum: ascending tracts from spinal cord to brain Descending: cerebral peduncles from cerebrum through brainstem to spinal cord Brainstem and the Reticular Formation Group of nuclei scattered throughout brainstem Controls cyclic activities such as sleep-wake cycle Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord Cerebellum Attached to brainstem posterior to pons Cerebellar peduncles: fiber tracts that communicate with other parts of brain Superior: to midbrain Middle: to pons Inferior: to medulla oblongata Gray cortex and nuclei with white matter (tracts) between Cortex folded in ridges called folia; white matter resembles a tree (arbor vitae) Purkinje Cells in Cerebellar Cortex Purkinje cells: largest in CNS. Receive 200,000 synapses, are inhibitory, only cerebellar cortex neurons that send axons to cerebellar nuclei Cortex has 1012 neurons; more than cerebral cortex Cerebellum Cerebellar Functions Flocculonodular lobe: balance and eye movements Vermis and medial portion of hemispheres: posture, locomotion, fine motor coordination leading to smooth, flowing movements Lateral hemispheres, major portion: works with cerebrum to plan, practice, learn complex movements Diencephalon Located between brainstem and cerebrum Components: thalamus, subthalamus, epithalamus, hypothalamus Diencephalon: Thalamus Two lateral portions connected by the intermediate mass Surrounded by third ventricle Sensory information from spinal cord synapses here before projecting to cerebrum Medial geniculate nucleus: auditory information Lateral geniculate nucleus: visual information Ventral posterior nucleus: most other types sensory information Motor function: ventral anterior and ventral lateral nuclei Mood modification: anterior and medial nuclei connected to limbic system Emotion regulation: lateral dorsal nucleus Sensory integration: lateral posterior and pulvinar nuclei Diencephalon: Subthalamus Involved in controlling motor function Contains subthalamic nuclei, parts of red nuclei and substantia nigra. Several ascending and descending nerve tracts Diencephalon: Epithalamus Habenula: emotional and visceral responses to odors Pineal gland: may influence sleepiness, helps regulate biological clock, may play a role in onset of puberty Diencephalon: Hypothalamus Most inferior portion of diencephalon Mammillary bodies: bulges on ventral surface; olfactory reflexes and emotional responses to odors Infundibulum: stalk extending from floor; connects hypothalamus to posterior pituitary gland. Controls endocrine system. Receives input from viscera, taste receptors, limbic system, nipples, external genitalia, and prefrontal cortex Efferent fibers to brainstem, spinal cord (autonomic system), through infundibulum to posterior pituitary, and to cranial nerves controlling swallowing and shivering Important in regulation of mood, emotion, sexual pleasure, satiation, rage, and fear Hypothalamus Cerebrum Largest portion of brain Composed of right and left hemispheres each of which has the following lobes: frontal, parietal, occipital, temporal, insula Sulci and Fissures Longitudinal fissure: separates the two hemispheres Lateral fissure: separates temporal lobe from frontal and parietal lobes Central sulcus: separates frontal and parietal lobes Cortex: outer surface Gyri are folds Sulci are depressions Medulla: center Nuclei: gray matter within the medulla Central sulcus: between the precentral gyrus (primary motor cortex) and postcentral gyrus (primary somatic sensory cortex) Frontal lobe: voluntary motor function, motivation, aggression, sense of smell, mood, personality and decision making Parietal lobe: reception and evaluation of sensory information except smell, hearing, and vision Occipital lobe: reception and integration of visual input Temporal lobe: reception and evaluation for smell and hearing; memory, abstract thought, judgment. Insula is within. Cerebrum Cerebral Cortex Thin (2?4 mm) superficial layer of gray matter 40% of the mass of the brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding Each hemisphere connects to contralateral side of the body There is specialization of cortical function in the hemispheres Cerebral Medulla White matter between the cortex and nuclei Association fibers: connections within the same hemisphere Commissural fibers: connect one hemisphere to the other Projection fibers: tracts between the cerebrum and other parts of the brain and spinal cord Basal Nuclei Found in the cerebrum, diencephalon, and midbrain Motor function control The nuclei in the cerebrum (caudate and lentiform) are called the corpus striatum Limbic System Part of cerebrum and diencephalon Basic survival functions such as memory, reproduction, nutrition Emotions In cerebrum: cingulate gyrus and hippocampus Various nuclei of the thalamus Part of the basal nuclei, hypothalamus, olfactory cortex, fornix Protection of the Brain Bone (skull) Membranes (meninges) Watery cushion (cerebrospinal fluid) Blood-brain barrier Meninges Cover and protect the CNS Contain cerebrospinal fluid (CSF) Form partitions in the skull Three layers Dura mater Arachnoid mater Pia mater Connective tissue membranes Dura mater: superficial Arachnoid mater Pia mater: bound tightly to brain Spaces Subdural: serous fluid Subarachnoid: CSF Meninges Cerebrospinal Fluid (CSF) Composition Watery solution Less protein and different ion concentrations than plasma Constant volume Functions Gives buoyancy to the CNS organs Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals Superior sagittal sinus Arachnoid villus Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle Central canal of spinal cord Choroid plexus Interventricular foramen Third ventricle Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture (a) CSF circulation CSF is produced by the choroid plexus of each ventricle. 1 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 2 CSF flows through the subarachnoid space. 3 CSF is absorbed into the dural venous sinuses via the arachnoid villi. 4 1 2 3 4 CSF Choroid Plexuses Produce CSF at a constant rate Hang from the roof of each ventricle Clusters of capillaries enclosed by pia mater and a layer of ependymal cells Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes Blood-Brain Barrier Regulates movement of materials from blood to brain Endothelial cells (lining all capillaries) have tight junctions between them. Astrocytes have foot processes that influence capillary permeability. Basement membrane of endothelium. These characteristics determine permeability: Lipid-soluble substances pass through by diffusion: nicotine, ethanol, heroin Water soluble substances move through by mediated transport: amino acids, glucose. Homeostatic Imbalances of the Brain Traumatic brain injuries Concussion?temporary alteration in function Contusion?permanent damage Subdural or subarachnoid hemorrhage?may force brain stem through the foramen magnum, resulting in death Cerebral edema?swelling of the brain associated with traumatic head injury Homeostatic Imbalances of the Brain Cerebrovascular accidents (CVAs)(strokes) Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot Typically leads to hemiplegia, or sensory and speed deficits Transient ischemic attacks (TIAs)?temporary episodes of reversible cerebral ischemia Tissue plasminogen activator (TPA) is the only approved treatment for stroke Homeostatic Imbalances of the Brain Degenerative brain disorders Alzheimer?s disease (AD): a progressive degenerative disease of the brain that results in dementia Parkinson?s disease: degeneration of the dopamine-releasing neurons of the substantia nigra Huntington?s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex Cranial Nerves Indicated by Roman numerals I-XII from anterior to posterior Names May have one or more of three functions (see 459-464) Sensory (special or general) Somatic motor (control of skeletal muscles) Parasympathetic (regulation of glands, smooth muscles, cardiac muscle)