Chapter 14 - The Peripheral Nervous System Flashcards
PNS structural components
Sensory receptors (detect stimuli) Motor endings (innervative effectors) Nerves and ganglia (bundles of axons and clusters of cell bodies)
Peripheral Sensory Receptors - Catagories
Free nerve endings
complete receptor cells
Free never endings
monitor most types of general sensory info (touch, pain, pressure, proprioception, temp)
Complete receptor cells
monitor special senses (taste, vision, hearing, balance)
Peripheral sensory receptors - location
exteroceptors
interoceptors
proprioceptors
exteroceptors
stimuli outside body
interoceptors
stimuli inside body
proprioceptors
musculoskeletal
Peripheral Sensory Receptors - stimulus detected
mechanoreceptors thermoreceptors chemoreceptors photoreceptors nociceptors
mechanoreceptors
mechanical forces
thermoreceptors
temperature
chemoreceptors
chemicals
photoreceptors
light
nociceptors
pain
Peripheral sensory receptors - structure
free nerve endings
encapsulated nerve endings
free nerve endings
abundant in epithelia and its corresponding CT mostly pain and temperature -merkel discs -hair follicle receptors -itch receptor (located in dermis)
Encapsulated nerve endings
one of more end fibers of sensory neurons enclosed in CT capsule
all are mechanoreceptors
amplify stimulus or filter stimuli
Encapsulated nerve endings - types
Meissner’s corpuscles
Pacinian corpuscles
Ruffini’s corpuscles
Proprioceptors
Meissner’s corpuscles
beneath epidermis, fine touch
mostly areas w/o hair
Pacinian corpuscles
located in deep CT
sense vibration
Ruffini’s corpuscles
located in dermis, joint capsules, hypodermis
monitor continuous pressure
Proprioceptors
muscle spindles - measure change in muscle length
golgi tendon organs (gto) - measure tension in tendon
joint kinesthetic receptors - measure stretch in synovial joints
Peripheral motor endings
skeletal muscle
visceral muscle and glands
skeletal muscle
one neuromuscular junction is associated with each muscle fiber
axon terminals release neurotransmitter, which crosses to sarcolemma
motor unit
a motor neuron and all the muscle fibers it innervates (all fibers contract)
Visceral muscle and glands
visceral motor axon swells into row of knobs (varicosities), releases neurotransmitter
Cranial Nerves
12 pairs, numbered I-XII (rostral to caudal)
First 2 pairs attach to forebrain, and the rest attach to the brain stem
generally serve head and neck with the exception of vagus
Mnemonic: Oh Oh Oh To Touch And Feel Very Good Velvet, AH
-Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, Hypoglossal
Olfactory I
Smell
sensory only
location: most superior, most anterior, arises from forebrain
Input goes to rhinencephalon
ONLY one that doesn’t go through thalamus
Optic II
VIsion sensory only input: rods and cones in retina, goes through thalamus, then to occipital lobe Arises from forebrain If severed blindness occurs
Oculomotor III
Primarily motor
Controls 4 of 6 muscles (skeletal) that move eye in orbit and iris (autonomic)
Somatic branch of nervous system
Arises from midbrain
If severed, eyelid may droop or person may not be able to move eyeball in certain direction
Trochlear (pulley) IV
small mixed nerve that comes from midbrain
innervates superior oblique muscle of eye which is responsible for downward and outward movement
damage impairs movement
Trigeminal V
mixed nerve - largest cranial nerve
arises from pons
splits into 3 different nerves (opthalamic, maxillary, mandibular)
motor functions deal with chewing
sensory functions are more extensive - info from skin and muscles of face, teeth
Is the novocain nerve numbed at dentist
Trauma to nerve can result in impaired chewing, lack of sensation from facial structures
Abducens VI
Originates from inferior pons
mostly motor
innervates lateral rectus muscle of eye (abducts)
damage causes crossed eyes (esotropia)
Facial VII
Arises from pons
mixed nerve
innervates muscles of facial expression
also innervates salivary glands - autonomic
taste sensation, anterior 2/3 of tongue
damage causes inability to contract facial muscles, distorted taste
Bell’s palsy (usually due to a virus): causes affected side of face to sag due to lost muscle tone
Vestibulocochlear VIII
The ONLY cranial nerve that does not exit cranium through a foramen
Purely sensory
arises from both pons and medullar
has 2 main branches: vestibular nerve (balance) cochlear nerve (hearing)
Glossopharyngeal IX
glossa = tongue; pharynx = throat
mixed nerve
originates in medulla
Innervates muscles of throat and tongue
also innervates salivary glands
controls taste in posterior 1/3 of tongue (bitter and sour)
damage causes loss of bitter and sour tasting, impairs swallowing
Vagus X
Arises from medulla
A mixed sensory and motor nerve
wanders into thorax and abdomen
parasympathetic innervation of organs
Goes through entire thoracic and abdominal cavity
KET autonomic nerve, mixed
If both vagus nerves are damaged, death would occur
Injury to one causes vocal impairment, difficulty swallowing, visceral issues
Accessory XI
Arises from medulla and part of spinal cord
motor only
moves head/neck/shoulder
damage makes it difficult to move shoulders, head
Hypoglossal XII
hypo = under; glossal = tongue motor only originates in medulla innervates tongue muscles if nerve is damaged, person will have difficulty in speaking, swallowing, protruding tongue
Spinal nerves
31 pairs (62 nerves)
exit spinal column via intervertebral foramina
c1-c7 leave the spinal cord ABOVE the corresponding vertebrae, BUT c8 leaves below c7, above T1
Thoracic, lumbar, sacral, and coccygeal all leave below corresponding vertebrae/bones
All are mixed nerves
The sensory and motor portions travel together, but enter and exit cord separately
afferents
sensory
enter cord via dorsal root
efferents
motor
exit cord via ventral root
Spinal nerve anatomy
Roots
Rami
Sypathetic rami
Roots
structures that enter and exit spinal cord
are sensory only or motor only
converge together in order to exit intervertebral foramen
rami
branches that occur after sensory and motor re-join
dorsal ramus - posterior
vertal ramus - anterior
sympathetic rami
2 branches from each spinal nerve that connects to sypathetic trunk ganglion, part of ANS
composed of a gray ramus and a white ramus
serve as place where sympathtic nerves separate from somatic motor neurons
can consider them like sideroads that carry impulses up and down between segments
Nerve plexuses
In most spinal nerves, (NOT T2-T12), the anterior rami combine and split again as plexuses
Network of nerves
Types of Nerve plexuses
Cervical
Brachial
Lumbar
Sacral
Cervical plexus
includes anterior rami of C1-C4 plus part of C5
branches of cervical plexus innervate skin and muscles of neck, portions of head and shoulders
Some fibers also combine with cranial nerves
Phernic nerve
Innervates diaphragm
sensory and motor
Brachial plexus
Primarily serves arm muscles, some neck and should
Formed mostly by C5-T1- very complex
Median nerve
innervates most muscles of anterior forearm and lateral palm
Lumbar plexus
Formed mostly by L1-L4
Serves muscles of abdomen, anterior/medial parts of leg
Obturator nerve
runs through obturator foramen
part of lumbar plexus
Sacral plexus
formed by L4-S5
serves muscles of pelvic area, posterior/lateral parts of leg, lower back, dorsal and plantar foot
Sciatic nerve
largest nerve in the body
passes through pelvis and down back of leg (composed of 2 nerves, tibial and common fibular)
Joint Innervation
Every joint capsule receives sensory branches from several nerves
Hilton’s law
Hilton’s law
Any nerve that innervates a muscle producing movement at a joint also innervates the joint itself (and the skin over it)
Dermatomes - Skin Innervation
Area of skin innervated by cutaneous branches from a single spinal nerve All spinal nerves except C1 involved Trunk region - horizontal Limb regions - vertical (sort of) Trunk dermatomes can overlap significantly; limbs less overlap Used clinically -pinpoint level of spinal injuries -anesthesia
PNS Disorders
shingles
myesthenia gravis
Shingles
Viral infection of sensory neurons involving the skin
Rash of scaly, painful blisters - along a dermatome
Stems from chickenpox, virus lies dormant in sensory ganglion
Myesthenia gravis
Disorder of neuromuscular junction
weakening of muscles
Autoimmune disorder (destroy Ach recptors in sarcolemma - no contraction)
