Nervous System 2

nerve

bundle of axons within epineurium (tissue sheath)

• within a nerve axons are subgrouped into fascicles surrounded by perineurium sheath

2 axon types

• motor - efferent - carries signal away from CNS and cell bodies alway in CNS

• sensory - afferent - carries signal towards CNS and cell bodies in PNS

pseudounipolar neuron

type of sensory neuron where cell body is located midway along axon and bifurcaes into peripheral and central parts

multipolar neuron

has 1 axon and 2 or more dendrites arising from cell body

nerve ganglion

collection of neuron cell bodies in PNS

mixed spinal nerve

contains both sensory and motor axons - separate before contact CNS

• sensory joins via dorsal root connecting to dorsal horn

• motor via ventral root to ventral horn

dorsal root ganglion

located on dorsal root of spinal nerve - slight swelling in nerve as houses cell bodies

nerve reflexes

1. sensory receptors

2. sensory neuron

3. interneuron

4. motor neuron

5. effector organ

spinal nerves

31 pairs - same amount as bones in spine sections except 8 cervical nerves

rami in spine

after dorsal and ventral roots combine to form mixed nerve then split into 4 branches (rami) - dorsal ramus, ventral ramus, grey ramus and white ramus

dorsal vs ventral rami

• dorsal = deep muscles and skin of back

• ventral = front and sides of trunk and all parts of limbs

grey vs white rami

• grey = unmyelinated and postganglionic = goes from sympathetic trunk to spinal nerve

• white - myelinated and preganglionic = goes from spinal nerve to trunk

dermatome

area of skin mainly supplied by single spinal nerve

myotome

group of muscles that a signle spinal nerve innervates

segmental innervation and why its clinically important

how specific segments of spinal cord connect to specific body parts thru spinal nerves

• can pinpoint exact site of spinal injury thru patterns of numbness, weakness or reflex changes

nerve plexus

branching network of intersecting nerves where they mix and redistribute = functional redundancy

• present at areas responsible for functions needed for survival

cranial nerves

12 pairs

• from cerebral hemisphere - olfactory 1 and optic 2

• from midbrain - oculomotor 3 and trochlear 4

• from pons - trigeminal 5, abducens 6, facial 7 and vestibulocochlear 8

• from medulla - vestibulochlear 8, glossopharyngeal 9, vagus 10, accessory 11 and hypoglossal 12

olfactory 1

sense of smell

optic 2

carries visual info from eye to brain

oculomotor 3

controls eye movement

trochlear 4

controls superior oblique muscle = eye can look up and down

trigeminal 5

3 branches that innervates face

abducens 6

controls outward eye movement

facial 7

motor control of face

vestibulocochlear 8

balance and hearing

glossopharyngeal 9

taste, inmervating pharynx = salivation and swallowing

vagus 10

parasympathetic control

accessory 11

controls sternocleidomastoid and trapezius muscles = turn head, tilt neck

hypoglossal 12

motor control of tongue

divisions of PNS

autonomic and somatic

somatic nervous system

voluntary muscle movements and processes external sensory info

autonomic nervous system

visceral involuntary functions. 2 divisions sympathetic and parasympathetic

sympathetic division

fright and flight - from thoracic or lumbar part of spine

• short preganglionic neuron

• long postganglionic neuron

nerves in sympathetic division

cell body of preganglionic neuron in lateral horn and leaves via ventral root (bc its motor neuron) travels into ventral rami>sympathetic rami>sympathetic trunk and synapse with postganglionic>target organ

parasympathetic division

rest and digest - from brainstem or sacral spine

• long preganglionic neuron

• short postganglionic neuron

nerves in parasympathetic division

preganglion leaves lateral via ventral root>ventral ramus>travels target organ where synapeses with postganglion