The Peripheral Nervous
System
Honors Anatomy & Physiology
Chapter 13
Classification of Sensory Receptors
by Stimulus Type
1.
Thermoreceptors:

2.
Mechanoreceptors:

3.
respond to light
Chemoreceptors:

5.
respond to mechanical force: touch, pressure,
vibration, stretch
Photoreceptors:

4.
respond to temperature change
respond to chemicals in solution
Nociceptors:

respond to pain
Pain Receptors

1.
2.
activated by:
extremes of pressure & temperature
Chemicals





histamine
K+
ATP
acids
bradykinin
Types of Pain
Sharp Pain

myelinated A delta
fibers
Burning Pain

unmyelinated C fibers
Referred Pain
pain stimuli arising in one part perceived
as pain from another part
 example: pain from heart attack can be felt
as pain in medial aspect of left arm
 cause: T1 – T5 spinal segments innervate
both

Cranial Nerves
12 paired on base
of brain
 name refers to
their function
 numbered by
Roman numerals

I and II attach to
forebrain
 III – XII brain stem

I - Olfactory Nerve
sensory only
 nasal mucosa  synapse in olfactory
bulbs




test: have patient smell ammonia
damage: anosmia (total loss)
olfactory receptors are bipolar
neurons
 each: single odor-sensitive
dendrite
II – Optic Nerve

sensory only
Optic Nerve - II


test:
 vision: eye chart
 visual fields: mark chart at point patient first
sees an object
 view fundus with opthalmoscopeto check for
swelling of optic disc (where optic n. leaves
eyeball) & examine blood vessels *only place
in body can directly visualize vessels
damage: II: blindess in affected eye
if beyond optic chiasma  partial loss
III - Oculomotor


“eye mover”
motor mostly (only
sensory
proprioceptors)


somatic  4 of 6
extrinsic eye muscles
parasympathetic 
circular muscles of iris
(constriction of pupil)
& to ciliary muscle
(controls shape of lens
for focusing)
III - Oculomotor


test: examine pupils for
size, shape, symmetry
damage:



eye cannot be moved up,
down, or inward; @ rest
eye rotates laterally
upper eyelid droops
(ptosis)
patient has double vision
&trouble focusing on
close objects
IV - Trochlear


“pulley”
motor


sensory:
proprioceptors
supplies extrinsic eye
muscle that loops
through a pulleyshaped ligament
(superior oblique
muscle)
IV – Trochlear Nerve
test: eye movement
 down & out
 damage: double
vision & impairs
ability to rotate eye
inferolaterally

V - Trigeminal



3 branches
largest cranial
nerve
sensory to
face/ motor to
chewing
muscles
V – Trigeminal Nerve
test: check blink reflex,
touch to side of face,
clench teeth, move jaw
side to side
 damage: trigeminal
neuralgia: worst pain
known, inflammation of
V, ? due to compression
by a vessel – treatment:
surgery

VI - Abducens


motor only
controls eye
muscle that
abducts
eyeball (lateral
rectus)
VI – Abducens Nerve
clinical test: check
eye movements
 damage: @ rest
eyeball rotates
medially on
affected side
(internal
strabismus)

VI – Abducens Nerve

normal test

abnormal test
VII - Facial

mixed


sensory: taste
anterior 2/3 of
tongue
motor: muscles
of facial
expression;
autonomic
motor: lacrimal
& salivary
glands
VII – Facial Nerve


clinical test: test taste in
anterior 2/3 of tongue,
check symmetry of face,
assess tearing (ammonia)
damage: Bell’s palsyparalysis of facial
muscles on affected side,
+/- continuous tearing
causing dry eye
Bell’s Palsy
? caused by herpes simplex
which causes swelling & inflammation of
facial nerve

treatment: corticosteroids
 clinically: ask patient to smile

VIII - Vestibulocochlear

mostly sensory: hearing & balance
VIII – Vestibulocochlear
clinically:
 check hearing by air &
bone conduction
 damage to

vestibular division 
dizziness, nystagmus,
loss of balance, nausea,
vomiting
 cochlear division
central deafness

IX – Glossopharyngeal Nerve


tongue & pharynx
mixed:


sensory: taste
posterior 2/3 tongue,
baroreceptors in
carotid sinus,
chemoreceptors in
carotid bodies
motor: upper pharynx,
autonomic fibers to
parotid glands
IX - Glossopharyngeal

test:




check position of uvula: will deviate away from
affected side when patient says “ahh”
check gag reflex
ask patient to speak & cough
taste check
X – Vagus Nerve


*only cranial nerve to extend beyond head &
neck
Mixed:


Motor: somatic to muscles of pharynx & larynx/
parasympathetic to heart (HR), lungs (RR), abd
viscera (peristalsis)
Sensory: from thoracic & abd viscera, chemoreceptors
for respiration (carotid & aortic bodies) and taste bud
in epiglottis, proprioceptors
X – Vagus Nerve



“the wanderer”
test: same as for IX
damage: hoarseness
or loss of voice,
dysphagia (difficulty
swallowing),impaired
digestive motility
XI – Accessory Nerve


motor
 trapezius &
sternocleidomastoid
 only sensory is
proprioception
emerges from spinal
cord (C1 – C5)  up
thru foramen magnum
 travels with X
XI – Accessory Nerve

test: injury to 1 side causes
head to turn to affected side
(sternocleidomastoid);
patient has weak shoulder
shrug on affected side
XII – Hypoglossal Nerve



“below tongue”
mostly motor: tongue: controls movements of
tongue that mix & manipulate food when
chewing, also contributes to speech & &
swallowing
test: protrude/ retract tongue, check for
deviations
Spinal Nerves

31 pairs:





8 cevical C1 – C8
12 thoracic T1 – T12
5 lumbar L1 – L5
5 sacral S1 – S 5
4 coccygeal Co1 – Co5
Spinal Roots

Ventral

motor (efferent) fibers  muscle

Dorsal

sensory (afferent)fibers  sensory receptors
both pass laterally from cord & the 2 unite to form a
spinal nerve (1-2 cm)

Rami (Ramus)



1.
2.
3.
ramus = branch
supply entire somatic region of body (skeletal
muscle & skin)
spinal nerve divides (1 -2 cm from vertebra) 
dorsal ramus:  posterior body
ventral ramus:  anterior body + limbs
meningeal branch: reenters vertebral canal to
innervate the meninges
Nerve Plexuses





all ventral rami (except T2- T12) branch & join
each other lateral to vertebrae forming
complicated nerve networks called: nerve
plexuses where fibers criss-cross (so each muscle
receives innervation from >1 spinal nerve)
cervical plexus
brachial plexus
lumbar plexus
sacral plexus
Nerve Plexuses
Reflex Arc