Laboratory 5 ? The Nervous System & Special Senses I. Central Nervous System neurons within brain are evenly distributed so that there are separate regions of grey & white matter gray matter is mostly interneurons but also contains cell bodies of motor neurons & unmyelinated fibers white matter contains bundles of myelinated fibers A. Brain 1. Prosencephalon/Forebrain a. Telencephalon i. Cerebral Hemispheres integration of sensory information; memory & cognition; voluntary movement ridges are gyri & grooves between are sulci (invaginations) convolutions increase brain?s surface area & number of neurons available for integrative processes surface is composed of gray matter; white matter lies beneath ii. Cerebral Cortex Right hemisphere Left hemisphere Left hemisphere Right hemisphere Medulla Parietal lobe Frontal lobe Temporal lobe Occipital lobe Cerebellum Spinal cord Pons Frontal Lobe motor & association areas Occipital Lobe visual centers Temporal Lobe hearing Parietal Lobe touch & position b. Diencephalon i. Thalamus relay for incoming sensory information; interacts with cerebral cortex in integrative mental processes ii. Hypothalamus contains centers for control of body temperature, appetite, fat metabolism, & certain emotions; regulates pituitary gland 2. Mesencephalon/Midbrain a. main association area; receives incoming sensory information, integrates it, & sends decisions to appropriate motor nerves b. makes up part of brain stem 3. Rhombencephalon/Forebrain a. Metencephalon Corpus callosum Cerebellum Thalamus Hypothalamus Optic chiasmaPons Medulla Pineal body Olfactory bulb Longitudinal fissure Frontal lobe Optic chiasma Temporal lobe Pons Medulla Cerebellum i. Pons regulate respiration; relay impulses from cerebrum to cerebellum ii. Cerebellum center of motor coordination ? muscular movements, muscle tone, & balance b. Myelencephalon i. Medulla oblongata regulates visceral activities (breathing movements, rate of heartbeat, blood pressure, swallowing, & salivation) 4. Olfactory bulb a. anterior part of rhiencephalon; concerned with sense of smell 5. Corpus callosum a. connects nonolfactory parts of cerebral hemispheres 6. Optic chiasma a. crossing of optic nerves b. ventral to corpus callosum B. Spinal Cord 1. Gray matter is by the central canal, & is surrounded by white matter 2. Axons of white matter belong to motor neurons which exit from ventral root, & Vertebral canal Neural spine of vertebra Spinal cord Dorsal root ganglion Body of vertebra Transverse Process Ventral root Dorsal root ganglion Dorsal root Gray matter White matter Central canal interneurons which transfer information along spinal cord into brain, being arranged in bundles known as tracts 3. Ventral root is composed of axons of motor neurons, while dorsal root is composed of axons of sensory neurons whose cell bodies lie within ganglion 4. Each spinal nerve divides into 2 branches: dorsal ramus & ventral ramus a. dorsal ramus supplies region of back musculature b. ventral ramus supplies limb & ventral musculature II. Peripheral Nervous System consists of all neural structures outside of CNS includes cranial & spinal nerves as well as autonomic & somatic nervous systems A. Reflex Arc combination of neurons that govern reflex automatic reflex actions 1. reception ? sense organ in skin, muscle, or other organ, signals sensory neuron 2. transmission ? sensory neuron transmits signal to CNS 3. integration ? interneuron integrates information 4. transmission ? appropriate motor neuron transmits impulses to muscle 5. action by effector ? muscle or gland produces actual response B. KneeJerk Reflex 1. antigravity response that maintains normal body orientation 2. when patellar tendon is struck, tendon fibers are stretched & activate golgi tendon organ (receptor) 3. action potential results, is carried toward spinal cord 4. within gray matter, sensory neuron synapses with interneuron. 5. interneuron synapses with one or more motor neurons, and action potential is Gray matter White matter Myelinated axons Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Dorsal root ganglion initiated in the motor neuron(s) 6. motor neurons carry action potential to various leg muscles, which contract and cause leg to extend III. Skin Receptors when a hair is moved it touches nerve endings & triggers an action potential registering the sensation of touch A. Meissner?s Corpuscles 1. touch receptors near skin surface that focus on light touch 2. located at tips of dermal papillae, fingerlike projections of dermis in epidermis 3. each corpuscle consists of a number of flattened layers of cells, each with elongated nucleus 4. when corpuscle is deformed by pressure, nerve endings are stimulated, registering sensation of touch B. Pacinian corpuscles 1. egglike structure consisting of many concentric layers of tissue a. embedded within is a free nerve ending 2. perceives deep pressure 3. when corpuscle is deformed by pressure, action potential is initiated in nerve ending 4. found in many areas of body, such as skin, mesenteries surrounding gut, & joint capsules 5. since fingertips are more sensitive to touch, they have higher densities of sensory Receptors C. Twopoint threshold 1. smallest distance between pins that allows subject to feel 2 points Epidermis Dermis Hair follicle Meissner corpuscles Dermis Pacinian corpuscle 2. tests distribution of sensory receptors in skin IV. Sensory Adaptation when certain sensory receptors are stimulated continuously, their response to the stimulus decreases & may eventually cease receptors for heat, cold, touch, & smell undergo adaptation V. Proprioception process of determining position, movements, & muscle condition of body proprioceptors are responsible for this process Pacinian corpuscles aid in reporting position of joints, which is interpreted by CNS to determine position of limbs & portions of body A. Muscle Spindle Fiber 1. spindleshaped, specially modified muscle fiber with bare nerve endings wrapped around it 2. when fibers are stretched, action potential is generated in nerve endings 3. body knows that certain muscle has been stretched 4. proprioceptive information received from stretch receptors in muscles & tendons, & Pacinian corpuscles in joints, is coordinated with visual input in brain to coordinate body position & movements VI. Eye Teased muscle tissue Muscle spindle fiber Vitreous humor Lens Sclera Choroid Cornea Suspensory ligament A. 3 layers of eye 1. white, tough outer sclera a. specialized anteriorly as transparent cornea 2. choroid coat a. dark, heavily pigmented layer which is specialized anteriorly to form iris & ciliary body b. absorbs excess light c. contains blood vessels that nourish eye 3. innermost membranous gray retina a. contains light sensitive cells B. Lens 1. biconvex, transparent; acts to focus light 2. cavity anterior to lens is filled with aqueous fluid 3. cavity between lens & retina is filled with viscous vitreous fluid C. Ciliary Body 1. thickened, ringshaped radially striated muscular area that curves to enclose lens 2. formed by choroid coat at front of eyeball 3. point of attachment of suspensory ligament, a thin membrane attached to lens around its equator 4. during accommodation, contraction of muscle fibers in ciliary body reduces pull on suspensory ligaments & thus on lens Pupil Iris Ciliary body Ciliary body Pupil Iris Retina attached at optic disc Lens Tapetum Optic disc a. allows naturally elastic lens to assume more rounded shape, bringing near objects into better focus 5. when muscles relax in ciliary body, they elongate a. exerts greater pull on suspensory ligament & lens, pulling lens into flatter shape, better adapted to distance vision D. Iris & Pupil 1. iris turns inward & covers front of lens 2. diameter of circular opening, the pupil, is regulated by contraction of circular & radial muscles in iris a. regulates amount of light admitted into retina E. Optic Disc/Blind Spot 1. sensory fibers from loose retina attached to wall of eye join to form optic nerve 2. where blood vessels pass into eye 3. no rods or cones in this area F. Tapetum 1. reflecting area that sends incident light back through retina a. makes efficient use of light 2. found in nocturnal terrestrial animals & fish G. Astigmatism 1. reflective error in which cornea has unequal curvature, causing vision to be out offocus H. Retina 1. Rods a. photoreceptor cells that function in dim light b. sensitive to light of all wavelengths 2. Cones a. photoreceptor cells responsible for color vision b. respond only to light of certain wavelengths c. 3 types of cones, red, blue, and green cones, respond maximally to light in red, blue, & green ranges, respectively d. since white light is mixture of all wavelengths, all cones are stimulated equally e. if no cones are stimulated, object perceived as black f. grays are perceived when cones are stimulated in low levels in various combinations 3. Colorblindness a. if one or more cone type is missing, its response will always be 0, & colors will be perceived accordingly b. most common type is redgreen colorblindness, in which either red or green cones are lacking i. individuals without red cones see bluegreens & purplish reds as gray condition known as protanopia ii. individuals without green cones see greens & purplereds as gray condition known as deuteranopia 4. Afterimage a. percept of visual stimulus after physical stimulus has been removed b. seen because color receptors cease to respond when stimulated continuously to particular color, so the neural response to that color is decreased, the response the opposing color is increased, & that color is brought out against a white background Christopher Laboratory 5 ? The Nervous System & Special Senses
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