FINISH . ANATOMY CH 14 PERIPHERAL NERVOUS SYSTEM

sensory receptors

• pick up stimuli from inside or outside the body

• afferent

nerves

• bundles of peripheral axons

  • cranial

  • spina

• most are mixed— sensory and motor nerves

ganglia

• clusters of peripheral neuron cell bodies

motor endings

• axon boutons (axon terminals/terminal boutons) of motor neurons

• innervates effectors— muscle fibers and glands

  • efferents

peripheral sensory receptors

• picks up sensory stimuli and transmits electrical signals into CNS

• two categories

  • free nerve endings of sensory neurons

    • monitors general sensory information

  • complete receptor cells

    • specialized epithelial cells or small neurons

    • picks up SPECIAL sensory information

exteroreceptors

• sensory receptors by location

• picks up info from outside the body

• located at or near body surfaces

  • receptors for touch, pressure, pain, and temperature

  • receptors of special sense organs

interoreceptors

• sensory receptors by location

• recieves info from inside the body— viscera

• licated in digestive tube, bladder, lungs

• monitor variety of stimuli

  • changes in chemical concentration— gases H+, salts

  • stretching of tissue

  • temperature

  • taste stimuli

proprioceptors

• sensory receptor by location

• also an encapsulated nerve ending/mechanoreceptor

• monitors degree of stretch in locomotory organs

• located in

  • skeletal muscles

  • tendons

  • joints

  • ligaments

• sends info to CNS

muscle spindles

• type of proprioceptor

• measures changing length of a muscle

• embedded in perimysium between muscle fascicles

• three types of fibers

  • INTRAFUSAL MUSCLE FIBERS— modified skeletal muscle fibers

  • ANNULOSPIRAL ENDINGS— located around intrafusal fibers, stimulated by rate and degree of stretch

  • FLOWER SPRAY ENDINGS— monitors spindle ends (contractile parts) responds only to degree of stretch

golgi tendon organs

• type of proprioceptor

• located near muscle-tendon junction

• monitors tension in tendons

joint kinesthetic receptors

• type of proprioceptor

• sensory nerve endings in joint capsules

• 4 types

  • lamellar corpuscles

  • bulbous corpuscles

  • free nerve endings

  • receptors resembling tendon organs

mechanoreceptors

• sensory receptor by stimulus

• responds to mechanical forces

  • touch, pressure, stretch, vibration, itch

  • BARORECEPTORS— monitors blood pressure

thermoreceptors

• sensory receptor by stimulus

• detects temperature

chemoreceptors

• sensory receptor by stimulus

• detects chemicals

  • taste

  • chemicals H+, NA+

  • smell

photoreceptors

• sensory receptor by stimulus

• responds to light

nociceptors

• sensory receptor by stimulus

• detects pain

free nerve endings

• sensory receptor by structure

  • also proprioceptors— joint kinesthetic receptors

• responds to pain and temperature

• itch receptors in dermis

epithelial tactile complexes

• modified free nerve ending

• slowly adapting mechanoreceptors for light touch

hair follicle receptors

• modified free nerve ending

• wraps around hair follicle

• rapidly adapting mechanoreceptors for light touch

  • bending of hairs

encapsulated nerve endings

• sensory receptor by structure

• enclosed in specialized CT capsules

  • amplifies stimulus or filters out irrelevant stimuli

• all mechanoreceptors

  • tactile (messiner’s) corpuscles

  • lamellar (pacinian) corpuscles

  • bulbous corpuscles (ruffini endings)

  • proprioceptors

tactile (messiner’s) corpuscles

• encapsulated nerve ending/mechanoreceptor

• spiraling neuron ending surrounded by unipolar schwann cells

• located in dermal papillae

• rapidly adapting

• receptors for fine, discriminative touch

• occurs in sensitive, hairless areas of skin

lamellar (pacinian) corpuscles

• encapsulated nerve ending/mechanoreceptor

  • also a proprioceptor— joint kinesthetic receptor

• single unipolar neuron ending surrounded by layers of schwann cells

• located in dermis

• rapidly adapting

• senses deep pressure and vibration

bulbous corpuscles (ruffini endings)

• encapsulated nerve ending/mechanoreceptor

  • also a proprioceptor— joint kinesthetic receptor

• located in dermis

• unipolar neuron ending enclosed in thin, flattened capsule

• slowly adapting receptors for pressure and touch

• monitors continuous pressure

cranial nerves

• nerves that attach to the brain and pass through specific foramina of the skull

  • CN I and II attach to forebrain; all others attach to brain stem

• primarily serves head and neck structures

  • CN X is the only cranial nerve that extends into abdomen

olfactory CN I

optic CN II

oculomotor CN III

trochlear CN IV

trigeminal CN V

abducens CN VI

facial CN VII

• pathway

  • enters temporal bone through internal acoustic meatus

• branches

  • temporal, zygomatic, buccal, mandibular, cervical

vestibulocochlear CN VIII

glossopharyngeal CN IX

• pathway

  • through jugular foramen to pharynx

vagus CN X

accessory CN XI

hypoglossal CN XII

spinal nerves

• 30 pairs of nerves that connect to spinal cord

• named for where they come out of spinal cord

  • 8 cervical pairs

    • C1 is superior to first verebra, but C8 is inferior to seventh vertebra

    • every spinal nerve below cervical region exits inferior to the vertebra of the same number

  • 12 thoracic pairs

  • 5 lumbar pairs

  • 5 sacral pairs

  • 1 coccygeal pair

dorsal root

• connects spinal nerves to spinal cord

• contains sensory fibers

  • cell bodies located in the ____ ___ ganglion

ventral root

• connects spinal nerves to spinal cord

• contains motor fibers

  • neuron cell bodies arising from anterior gray column

dorsal and ventral rami

• spinal nerves branching

• both contain sensory and motor fibers

rami communicantes

• connects spinal nerves to sympathetic chain ganglia

dorsal rami

• innervates deep back muscles

  • follows a neat segmented pattern in line with their emergence point from vertebral column

ventral rami

• innervates anterior thoracic and abdominal wall

  • only in thoracic region

  • arranged in simple segmented pattern

  • runs anteriorly, one deep to each rib— INTERCOSTAL NERVES

    • each gives off lateral and anterior CUTANEOUS branches to the skin

hilton’s law

• states that a joint is innervated by any nerve that innervates the muscles that move it or skin over it

nerve plexus

• network of nerves

• formed by ventral rami of all spinal nerves

  • except T2-T12

• occur in 4 regions

  • CERVICAL

  • BRACHIAL

  • LUMBAR

  • SACRAL

• fibers from ventral rami converge, diverge, and redistribute

  • each muscle in a limb receives its nerve supply from more than one spinal nerve

cervical plexus

• nerve plexus

  • deep to sternocleidomastoid, extends into posterior triangle of the neck

• formed by ventral rami of first four cervical nerves (C1-C4)

  • most are sensory cutaneous nerves of the neck, back of head, and superior part of the shoulder

  • some innervate muscles of the anterior back

phrenic nerve

• nerve of cervical plexus

  • most important nerve of plexus

  • formed from C3-C5

  • provides somatic motor and sensory innervation to the diaphragm

brachial plexus

• nerve plexus that innervates upper limb

  • lies partially in neck and axilla

• formed by ventral rami of cervical nerves C5-C8 and most of the ventral ramus of T1

  • may recieve small contributions from C4 or T2

• cords give rise to main nerves of the upper limb

  • roots/rami, trunks, divisions, cords (really tired drink coffee)

lateral and medial cords

• brachial plexus cords composed of nerves

  • musculotaneous

  • median (both cords)

  • ulnar

posterior cord

• brachial plexus cord composed of nerves

  • axillary

  • radial

lumbar plexus

• nerve plexus that innervates lower limb

  • L1-L4

  • lies within psoas major muscle in the posterior abdominal wall

• smaller branches innervate the posterior abdominal wall and psoas muscle

• two main branches

  • femoral nerve

  • obturator nerve

sacral plexus

• nerve plexus that innervates lower limb

  • arises from L4-S4

  • caudal to the lumbar plexus

• some fibers from the lumbar plexus contribute to this plexus via LUMBOSACRAL TRUNK

  • the two plexuses are often considered together

• nerves branch from SCIATIC NERVE

  • TIBIAL NERVE

    • medial and lateral plantar nerves on sole of foot

  • COMMON FIBULAR NERVE

• supplies all of the muscles in the posterior region of lower limb

• supplies cutaneous innervation on the posterior leg/sole of foot

superior and inferior gluteual nerves

• sacral plexus nerves

• innervates gluteal muscles

pudendal nerve

• sacral plexus nerve

• innervates muscles of the perineum

  • stimulate erection, voluntary inhibition of defecation and urination

dermatome

• region of skin innervated by a single spinal nerve

  • innervated by all cutaneous branches of a single spinal nerve except C1

  • named by spinal nerve level

  • for lower limb— lumbar nerves innervate anterior surface; sacral nerves innervate posterior surface

shingles (herpes zoster)

• disorder of the PNS

  • viral infection

  • stems from childhood chicken pox

  • often brought on by stress

  • mostly experienced by people over age 50

migane headache

• disorder of the PNS

  • relates to sensory innervation of the cerebral arteries

  • arteries dilate, compress, and irritate sensory nerve endings

peripheral neuropathy

• disorder of the PNS

  • pathological condition of peripheral nerves

• symptoms of sensory nerve involvement

  • parasthesia, pain, burning, loss of sensation

• symptoms of motor nerve involvement

  • muscle weakness and paralysis

• causes

  • trauma, repetitive use

  • systemic disorders

    • HIV, diabetes, vitamin B deficiency