peripheral nerves

the brain, the spinal cord and the peripheral nervous system work together as a communication system.

spinal cord

continuation of the brain stem

17 inches long and extends from the foremen magnum to the level of the first lumbar vertebrae

gray matter

central- canal- opening or hold that extends the entire length of the spinal cord

white matter

composed primarily of myelinated axons

asending tracts

carry information from the periphery, up the spinal cord and toward the brain

(a sensory tract)

depending tract

carries information from the brain, down the spinal cord, and toward the periphery

(motor tracts)

decussation

the crossing over from one side to the other

the spinal cord serves three main functions

sensory pathway, motor pathway, and reflex center

motor pathway

spinal cord provides a pathway for information coming from the brain and going to the periphery

reflex center

the spinal acts as a major reflex center.

involuntary response to a stimulus

patellar or knee jerk reflex

in response to a tap on you're kneecap , your lower leg quickly and involuntarily pops up

pupillary reflex

regulates the amount of light that enters the eye

baroreceptor reflex

when blood pressure changes, these reflexes cause the heart and blood vessels to respond in a way that restores blood pressure to normal

peripheral nervous system nerves

• sensory nerves- composed only of sensory neurons
• motor nerves- composed only of motor neurons
• mixed neurons- contains both sensory and motor neurons

cranial nerve: Olfactory

a sensory nerve that carries information from the nose to the brain

concerned with the sense of smell

cranial nerve: II optic nerve

sensory nerve that carries visual information from the eye to the brain

cranial nerve: III oculomotor

primarily a motor nerve that causes contraction of the extrinsic eye muscles, thereby moving the eyeball in the socket

cranial nerve: IV trochlear

primarily a motor nerve that innervates one of the extrinsic muscles of the eyeball, helps move the eyeball

cranial nerve: V trigeminal

carry information regarding touch, pressure and pain from the face, scalp, eye and teeth to the brain

cranial nerve: VI abducens

primarily a motor nerve, controls eye movement by innervating only one of the extrinsic eye muscles

cranial nerve: VII facial

the nerve of facial expressions that allows us to smile, frown and make other faces

cranial nevre: vestibulocohlear

carries information for hearing and balance from the inner ear to the brain

cranial nerve: IX glossopharyngeal

carries taste sensations from the posterior tongue to the brain

associated with gag reflex

cranial nerve: X vagus

a mixed nerve that innervates the tongue, pharynx, larynx, and many organs in the thoracic and abdominal cavities

cranial nerve: XI accessory

primarily a motor nerve that supplies the sternocleidomastoid and the trapezius muscles

cranial nerve: XII hypoglossal

primarily a motor nerve that controls movement of the tongue

31 Pais of spinal nerves emerge from the spinal cord and they are:

• 8 pairs of cervical nerves
• 12 pairs of thoracic nerves
• 5 pairs of lumbar nerves
• 5 pairs of sacral nerves
• 1 pair of coccygeal nerves

plexuses

points where nerve fibers converge together

three major nerve plexuses

• cervical plexus
• brachial plexus
• lumbosacral plexus