Topic 21 Central Nervous System PPT Part 3

cranial nerves

12 pair of nerves

arise from brain

exit through foramina leading to muscles, glands and sense organs in head and neck

olfactory nerve I

sensory fibers only

sense of smell

damage causes impaired sense of smell

optic nerve II

sensory fibers only

visual acuity

damage causes blindness in visual field

oculomotor nerve III

motor fibers

eye movement, opening of eyelid, constriction of pupil, focusing

damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing and inability to move eye in certain directions

trochlear nerve IV

motor fibers only

eye movement

damage causes double vision and inability to rotate eye down and in

trigeminal nerve V

both sensory and motor fibers

sensory to face: touch, pain and temp

motor: muscles of mastication

abducens nerve VI

motor fibers only

provides eye movement

damage results in inability to rotate eye laterally and at rest eye rotates medially

facial nerve VII

both sensory and motor fibers

motor - facial expressions; salivary glands and tear, nasal and patine glands

sensory - taste of tongue

damage produces sagging facial muscles and disturbed sense of taste

ball’s palsy

disorder of facial nerve causes paralysis of facial muscles on one side may appear abruptly with full recovery within 3-5 weeks

vestibulocochclear nerve VIII

sensory fibers only

provides hearing and sense of balance

damage produces deafness, dizziness, nausea, loss of balance

glossopharyngeal nerve

both sensory and motor fibers

swallowing, salivation, gaging, control of BP

sensations from tongue

damage results in loss of bitter and sour taste and impaired swallowing

vagus nerve X

both sensory and motor fibers

swallowing, speech, regulation of viscera

damage causes hoarseness or loss of voice, impaired swallowing and fatal if both are cut

accessory nerve XI

motor fibers only

wallowing, head, neck and shoulder movement

damage causes impaired head, neck, shoulder movement; head turns toward injured side

hypoglossal nerve XII

tongue movements for speech, food manipulation and swallowing

types of stimuli and sensations

take many forms: physical force, dissolved chemical, sound, light

sensations: taste, hearing, vision. communicate with sensory neurons across chemical synapses

tonic receptors

always active

phasic receptors

inactive

become active for a short time when change occurs

provide information about intensity and rate of change of stimulus

adaptation

reception in sensitive of a content stimulus

nervous system quickly adapts to stimuli that are painless and constant

major receptor types

divides the vernal sensory receptors into 4 types by the nature of the stimulus that excites them

nociceptors

pain

thermoreceptors

temperature

mechanoreceptors

physical distortion

chemoreceptors

chemical concentration

pain receptors

common in superficial portion of skin, joint capsules, periosteum of bones

sensitive to temperature, mechanical damage, dissolved chemicals

myelinated type a pain receptors

type a fibers

carry sensation of fast pain

sensations reach cns quickly and trigger somatic reflexes

type c pain fibers

carry sensations of slow pain

thermoreceptors

conducted along same pathway as pain sensations

free nerve endings location in dermis, skeletal muscles, liver

mechanoreceptors

sense to stimuli that distort their cell membranes

contain mechanically regulated ion channels whose gates open or close in response to stretching compression twisting

3 classes of mechanoreceptors

tactile receptors, baroreceptors, proprioceptors

tactile receptors

prove the sensations of touch, pressure, and vibration

baroreceptors

detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts

prorioceptors

monitor the positions of joints and muscles

the most structurally and functionally complex of sensory receptors

spinal cord anatomy

exterior white matter - conduction tracts

internal gray matter - mostly cell bodies

somatic sensory pathways

carry sensory information from the skin and musculature of the body wall, head, neck and limbs

motor pathways

always involve at least 2 motor neurons - upper motor neuron and lower

upper motor neuron

cell body lies in a CNS processing center

lower motor neuron

cell body lies in a nucleus of the brain stem or spinal cord

corticospinal pathway

provides voluntary control over skeletal muscles

lateral and anterior