the peripheral nervous system

PNS

consists of all neural structures outside brain and spinal cord

spinal nerves

31 pairs, from spinal cord roots

cranial nerves

12 pairs

autonomic nervous system

sympathetic and parasympathetic

sympathetic

flight or fight

parasympathetic

rest and digest

sensory receptors

specialized to respond to changes in environment

mechanoreceptors

touch, pressure, vibration, and stretch

thermoreceptors

changes in temperature

photoreceptors

light energy (ex. retina)

chemoreceptors

chemicals (smell, taste, blood chemistry)

nociceptors

pain-causing stimuli (extreme heat or cold, excessive pressure, inflammatory chemicals)

exteroceptors

outside body, receptors in skin for touch, pressure, pain, temperature, and most special sense organs

interoceptors

internal viscera and blood vessels, sometimes cause discomfort but usually person is unaware of their workings

proprioceptors

stretch in skeletal muscles, tendons, joints, ligaments, informs brain of one’s movements

general sense receptors

touch, found throughout body and monitor most types of general sensory information

free nerve endings

superficial dermis, lower epidermis, pain and temperature

Meissner’s corpuscle

fast-adapting, superficial dermis (papillae), light touch (fingertips)

Pacinian corpuscle

lower dermis and subcutaneous tissue, deep pressure and vibration

Ruffini endings

lower dermis, skin stretch and pressure

Merkle’s discs

slow-adapting, superficial dermis, shape, texture, sustained pressure

receptors for special sense

vision, hearing, equilibrium, smell and taste

nerve

cordlike organ of PNS, bundle of myelinated and non-myelinated peripheral axons

two types of nerves

spinal and cranial

epineurium

surrounds fascicles to form nerve

perineurium

bundles fibers into fascicles

endoneurium

encloses axons and myelin sheaths

mixed nerves

sensory and motor fibers, impulses travel to and from CNS

sensory (afferent) nerve

impulses toward CNS, somatic or visceral

motor (efferent) nerve

impulses way from CNS, somatic or visceral

if soma (cell body) is intact, the peripheral axon may regenerate in

PNS, not CNS

olfactory nerve

sensory nerves of smell, run from nasal mucosa to olfactory bulbs, terminates in temporal lobe

optic nerve

sensory nerve of vision, arise from retinas, partially cross over at optic chiasma, optic tracts continue to thalamus, fibers run to occipital lobe

oculomotor nerve

fibers extend to four extrinsic eye muscles, raising eyelid, directing eyeball, constricting iris (parasympathetic), controlling lens shape

trochlear nerve

innervate superior oblique muscle, look down and out

abducens nerve

innervating lateral rectus muscle, look sideways

trigeminal nerve

motor nerve, largest cranial nerve, innervation of muscles of mastication

ophthalmic

forehead sensation

maxillary

cheek sensation

mandibular

lower jaw sensation

facial nerve

motor and sensory, five branches, facial expression, parasympathetic impulses to lacrimal and salivary glands, taste function from anterior tongue

vestibulocochlear nerve

cochlear for hearing, vestibular for balance/equilibrium, mostly sensory

glossopharyngeal nerve

motor and sensory, tongue and pharynx for swallowing, parasympathetic fibers to parotid salivary glands, taste and sensory from pharynx and posterior tongue

vagus nerve

motor and sensory, parasympathetic activities in heart lungs and abdominal viscera, thoracic and visceral sensory information, cardio, taste buds

accessory nerve

formed from nerve roots of cervical spinal cord (not brain), innervate trapezius and sternocleidomastoid

hypoglossal nerve

innervate tongue muscles for swallowing and speech

nerve plexuses

group of nerves formed from ventral rami of various adjacent spinal nerve levels

cervical plexus

C1-C4, mostly cutaneous, innervate skin of neck, ear, back of head, and shoulders

phrenic nerve

major nerve of diaphragm, breathing

brachial plexus

C5-C8 and T1, gives rise to nerves that innervate upper limb, Randy Travis Drinks Cold Beer (roots, trunks, divisions, cords, branches)

axillary

deltoid, teres minor, and skin and joint capsule of shouler

musculocutaneous

biceps brachii and brachialis, coracobrachialis, and skin of lateral forearm

median

flexors/pronators of wrist/fingers, skin of thumb, index and middle finger

ulnar

flexor carpi ulnaris, intrinsic hand muscles, skin of pinky and ring finger

radial

extensor muscles/supinator of wrist, posterior skin of hand

lumbar plexus

L1 to L4, mostly lower limb, some branches to abdomen, pelvis, and buttocks, femoral and obturator nerve

sacral plexus

L4 to S4, buttock lower limb pelvic structures and perineum

sciatic nerve

longest and thickest nerve, innervates hamstring and leg and foot, tibial and common fibular nerves

sciatica

stabbing pain radiating in posterior thigh, leg, and foot, may experience footdrop, recovery is slow and incomplete

dermatomes

innervation of skin, all spinal nerves except C1

reflex arc

receptor, sensory neurons, integration center, motor neuron, and effector

deep tendon reflexes

occur without direct involvement of higher brain centers, testing of somatic reflexes important clinically to assess condition of nervous system

Babinski’s sign

superficial reflexes elicited by gentle cutaneous stimulation of area, important for signaling problems in upper motor pathways or cord-level reflex arcs

plantar reflex

stroke sole of foot, downward flexion of toes, big toe dorsiflexes and smaller toes fan laterally