Anatomy Chapter 5.docx

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Biological Sciences
Connie Soros

Chapter 5 Central Nervous System • A "wired" system - specific pathways for transmission of signals between areas of body - In general, coordinates rapid, precise responses - interacts with endocrine system ("wireless") • Organization of nervous system - central nervous system (CNS) 1. brain and spinal cord - peripheral nervous system (PNS) 1. nerve fibers carry information between CNS and rest of body 2. afferent (sensory) division a. carries information toward CNS 3. efferent (motor) division a. carries information away from CNS to effector organs (muscles, glands) b. somatic nervous system (1) motor neurons supplying muscles c. autonomic nervous system (1) innervates smooth and cardiac muscle, glands (2) sympathetic division ("fight or flight") (3) parasympathetic division ("resting and digesting") • 3 Classes of neurons - afferent 1. in afferent division of PNS 2. peripheral end has a sensory receptor a. generates APs in response to a stimulus 3. cell body near spinal cord 4. synapses with other neurons in spinal cord - efferent 1. in efferent division of PNS 2. cell body in CNS 3. terminates at a muscle or gland - interneurons (most neurons) 1. in CNS, between afferent and efferent neurons 2. interconnect with one another • Protection /nourishment of the brain - glial cells (neuroglia) 1. astrocytes a. hold neurons together b. induce changes in blood vessels (blood-brain barrier) c. repair of injury and scar formation d. take up and break down some nts (glutamate, GABA) e. take up excess K in ECF f. have receptors for nts - may be communication among glial cells and between glial cells and neurons 2. oligodendrocytes a. forms myelin sheaths 3. ependymal cells a. line internal cavities of CNS (ventricles of brain, central canal of spinal cord) b. help form cerebrospinal fluid (CSF) c. serve as stem cells in some areas of brain 4. microglia a. defense cells - blood-brain barrier 1. capillaries in brain have tight junctions joining cells a. only substances that can pass through cells can be exchanged (lipid soluble substances, e.g., O , CO , alcohol, steroid hormones; substances with specific carriers, 2 2 e.g., glucose, amino acids, ions) 2. protects brain from harmful substances 3. keeps out circulating hormones that act like nts - CSF 1. formed by choroid plexuses, surrounds brain and spinal cord 2. cushions CNS 3. it is the interstitial fluid of the CNS a. directly contacts CNS cells and exchanges take place + + 4. similar to plasma, but lower in K and higher in Na - meninges: connective tissue membranes 1. dura mater - outer layer a. forms dural sinuses and venous sinuses (blood and CSF pool, return to circulation) 2. arachnoid mater - middle layer a. subarachnoid space contains CSF b. arachnoid villi reabsorb CSF (return to blood in sinuses) 3. pia mater - inner layer a. well vascularized b. important in forming CSF - bones offer physical protection 1. cranium (skull) - brain 2. vertebral column - spinal cord • brain structure • Cerebrum - cortex is outer layer of gray matter (neuron cell bodies and dendrites, glial cells) - underneath is white matter (tracts of myelinated fibers), which transmits signals between cortical areas, and to other CNS locations - divided into functional areas (some degree of overlap) specialized for particular activities, but no area acts alone - 2 hemispheres 1. connected by corpus callosum 2. most functional areas occur in both hemispheres (except language areas) 3. some degree of specialization a. left - logical, analytical tasks like language, math; fine motor control b. right - nonlanguage skills like spatial perception and art/music 4. generally involved in functions of opposite side of body (contralateral) - paired lobes 1. occipital, temporal, parietal, frontal 2. functional areas often contained within a lobe - 3 kinds of functional areas 1. motor areas - control voluntary motor functions 2. sensory areas - conscious awareness of sensation 3. association areas - integrate diverse information - selected functional areas 1. primary visual cortex a. receives visual information b. surrounding higher-order visual cortex interprets 2. primary auditory cortex a. receives information on sound b. surrounding higher-order auditory cortex interprets 3. somatosensory cortex a. receives sensory input (somesthetic sensations from skin like touch, temp. and proprioception, etc.) (1) localizes source of input, perceives intensity of stimulus, capable of spatial discrimination (2) sensory homunculus - a particular region of the brain receives information from a certain part of the body 4. posterior parietal cortex a. integrates somatosensory and visual input b. important in complex movement 5. primary motor cortex a. voluntary control of skeletal muscle (1) motor homunculus - neurons controlling a particular body part tend to be grouped together 6. supplementary motor area a. helps prepare "programs" for complex patterns of movement 7. premotor cortex a. plans movement based on body orientation, coordination of complex movements b. interacts with posterior parietal cortex 8. Language areas a. Broca's area (1) important in preparing to speak - interacts with motor areas for speech b. Wernicke's area (1) important in language comprehension and sounding out unfamiliar words (2) receives input from visual cortex and auditory cortex c. Broca's and Wernicke's usually in left hemisphere only, right side has affective language areas, which express and comprehend emotion in speech 9. prefrontal association cortex a. plans for voluntary activities b. weighing consequences, making choices c. personality d. complex learning, intellect (cognition), conscience 10. parietal-temporal-occipital association cortex a. integrates information from those lobes 11. limbic association cortex a. motivation, emotion, memory - cortex displays plasticity 1. many areas can change based on need, e.g.: a. other areas may take over for damaged areas b. use of a particular body part can result in more cortical space being devoted to it - areas constantly interact • Subcortical structures - basal nuclei (basal ganglia) 1. masses of gray matter within cerebral white matter 2. functional aggregations of cell bodies a. inhibiting muscle tone b. maintaining purposeful motor activity and suppressing unnecessary movement c. monitor/coordinate muscle contractions in posture/support d. complex aspects of motor control e. may be involved in cognitive functioning 3. receive
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