peripheral nervous system (PNS)

functions of PNS

connects the nervous system to organs, limbs, and skin

carries sensory motor info to and from CNS

regulates involuntary body functions (heart rate and breathing)

lets brain and spinal cord receive and send info to other areas of body

spinal nerves

are mixed containing both sensory & motor axons

31 pairs are mixed with sensory afferents & motor efferents

DAVE

D = Dorsal

A = Afferents

V = Ventral

E = Efferents

SAME

S = Sensory

A = Afferents

M = Motor

E= Efferents

somatic afferent

sensory: skin & skeletal muscle to brain

somatic efferent

motor: brain to skeletal muscle

visceral afferent

sensory: internal organs to braintransmits sensations from organs

visceral efferent

motor: brain to internal organs

31 pairs of spinal nerves

mixed nerves and named for where they leave the spinal cord

supply body parts except head and part of neckand are responsible for both sensory and motor functions.

8 pairs of cervical nerves (C1-C8)

cervical and brachial plexuses

12 pairs of thoracic nerves (T1-T12)

thoracic plexus

5 pairs of lumbar nerves (L1-L5)

lumbar plexus

5 pairs of sacral nerves (S1-S5)

sacral plexus

1 pair of tiny coccygeal nerves (CO1)

coccygeal plexus

spinal cord processing to the brain

if sensory info is too complex to be processed with reflex arc it will be sent to brain

ascending tracts (sensory tracts) groups of myelinated axons that take info up

apart of white matter of the spinal cord

correct response from brain

it will be sent back to spinal cord

descending tracts (motor tracts) groups of myelinated axons that take info down

apart of white matter of spinal cord

spinal cord reflexes

nervous system must receive proprioceptor regarding:

length of muscle (info sent from muscle spindles

amount of tension in muscle (info sent from tendon organs)

stretch (extensor) reflex

are mono synaptic ipsilateral reflexes

step 1 of patellar reflex

tapping patellar ligament stretches quadriceps and excites muscle indles

step 2 of patellar reflex

afferent impulses travel to spinal cord where synapses occur with motor neurons and interneurons

step 3 of patellar reflex

motor neurons send activating impulses to quadriceps causing it to contract extending the knee

step 4 of patellar reflex

interneurons make inhibitory synapses with ventral horn neurons that prevent antagonist muscles from resisting contraction of quadriceps

withdrawal (flexor) reflexes

polysynaptic ipsilateral reflexes

protective and important for survival

brain can override these

cross-extensor reflexes

polysynaptic contralateral reflexes

occur with withdrawal reflexes to shift body weight towards opposite side

superficial reflexes

elicited by gentle cutaneous stimulation of the area

used to test for problems with spinal cord-level reflexes

best example plantar reflex

Babinski’s sign

infants exhibit it until 1 years old because nervous systems are not completely myelinated

spinal cord processing to brain part 1

sensory receptors detect stimulus

spinal cord processing to brain part 2

action potentials transmit along axons into dorsal root of spinal nerve

spinal cord processing to brain part 3

action potentials transmitted along sensory axons in white matter ascending the brain

spinal cord processing to brain part 4

sensory axons extend into gray matter synapse with interneurons whose axons extend to white matter and ascend to the brain

spinal cord processing to brain part 5-6

axons from brain form motor tracts descending into white matter synapsing with somatic motor neurons leaving through ventral root of spinal nerve

cranial nerves

has 12 pairs

3 sensory

4 mixed

5 motor

sensory cranial nerves

olfactory

optic

vestibulocochlear

mixed cranial nerves

trigeminal

facial

glossopharyngeal

vagus

motor cranial nerves

oculomotor

trochlear

abducens

accessory

hypoglossal

olfactory

sense of smell

sensory nerve

optic

vision

sensory nerve

oculomotor

eye movements by controlling 4 of extraocular muscles lifting the upper eyelid when the eye points up and for pupillary constriction

motor nerve

trochlear

eye movement but control different extraocular muscles

motor nerve

trigeminal

cutaneous sensations of face and controlling muscles of mastication

mixed nerve

abudcens

eye movement but controls different extraocular muscles

motor nerve

facial

muscles involved in facial expressions and part of sense of taste and production of saliva

mixed nerve

vestibulocochlear

senses of hearing and balance

sensory nerve

glossopharyngeal

controls muscles in oral cavity and upper throat and part of sense of taste and producing saliva

mixed nerve

vagus

homeostatic control of organs of thoracic and upper abdominal cavities

mixed nerve

accessory

controls muscles of neck and cervical spinal nerves

motor nerve

hypoglossal

controls muscles of lower throat and tongue

motor nerve

segmental level motor control

example : reflexes

controls automatic motor responses

projection level motor control

includes cerebrum & brainstem

can control segmental-level responses

both voluntary & involuntary motor responses can originate here

pre-command level motor control

are complex coordinated movements that are required

cerebellum & basal nuclei exhibit this level of control

tells the cerebrum how to do the action it wants