Chapter 14
Peripheral nervous system
Introduction
 Consist of: Cranial and spinal nerves
 PNS made Somatic - oversees voluntary
activities of
 Autonomic - controls involuntary
activities.
Spinal nerves
 31 pair - connected to spinal cord
 Numbered in sequence
 Eight cervical nerve pairs (C1 through C8)
 Twelve thoracic nerve pairs (T1 through
T12)
 Five lumbar nerve pairs (L1 through L5)
 Five sacral nerve pairs (S1 through S5)
 One coccygeal nerve pair
 Each spinal nerve arises from Two roots
 dorsal - sensory (carries information to CNS)
 Ventral - motor(carries information from CNS
to efector)
 Nerve Plexus
 Cervical
 Brachial
 lumbrosacral
Dermatomes and myotomes
 Dermatomes - section of skin
innervated by a single spinal nerve
 Myotome - segment of muscle
innervated by a single spinal nerve
Cranial nerves
 12 pair
 Designated by number and name
 Olfactory nerve (I)
 Carries information about sense of
smell
 Optic nerve (II)
 Carries visual information from the
eyes to the brain
 Oculomotor nerve (III)
 external eye muscles
 regulate amount of light entering eye and
aid in focusing on near objects
 Trochlear nerve (IV)
 oblique muscles of the eye
 Trigeminal nerve (V)
 Sensory from skin of head/teeth,
chewing
 Abducens nerve (VI)
 muscles of the eye
Cranial Nerves cont’d
 Facial nerve (VII)
 superficial muscles of the face and scalp (Figure 14-11)
 salivary glands
 sensory fibers from taste buds
 Vestibulocochlear nerve (VIII)
 Two distinct divisions that are both sensory: vestibular nerve
and cochlear nerve:
 Vestibular nerve - semicircular canals in inner ear and transmit
impulses that result in sensations of equilibrium
 Cochlear nerve - sensations of hearing
 Glossopharyngeal nerve (IX)
 Supplies fibers to tongue, pharynx, and carotid sinus
 Vagus nerve (X)
 widely distributed branches
 pharynx, larynx, trachea, heart, carotid body, lungs,
bronchi, esophagus, stomach, small intestine, and
gallbladder
Cranial Nerves cont’d
 Accessory nerve (XI)
 Motor nerve that is an “accessory” to the
vagus nerve
 Innervates thoracic and abdominal viscera,
pharynx, larynx, trapezius, and
sternocleidomastoid
 Hypoglossal nerve (XII)
 Motor fibers innervate the muscles of the
tongue
 Contains sensory fibers from proprioceptors in
muscles of the tongue
Divisions of peripheral
nervous system
 Afferent - Sensory
 Efferent - Motor
 Somatic - under conscious control
 Autonomic - not under conscious control
Somatic
 Skeletal muscle innervation
 Acetylcholine is the neurotransmitter
 Somatic Reflexes
 Cranial - processed in brain
 Spinal-processed in spine
 Somatic reflex-involves skeletal muscle
 Autonomic reflex-involves smooth muscle,
cardiac muscle or gland.
Autonomic nervous system
 Function maintaining
homeostasis of
visceral activities
 Two divisions
 Sympathetic - stress
or emergency
 Parasympathetic normal conditions
Autonomic nerve fibers
 Sympathetic division-come
from thoracic and lumbar
regions
 Parasympathetic divisionarise from brain stem and
sacral regions
 Autonomic neurotransmitters
 Acetylcholine - used for
sympathetic and
parasympathetic
 Norepinephrine, epinephrine
from adrenal gland - used for
sympathetic
 Hormone - cortisol
Fight or flight - the stress
response
QuickTime™ and a
decompressor
are needed to see this picture.
Fight or flight








Increased heart rate
Coronary vessel dilation
Vascular dilation in muscles
Spleen contraction
Dilation of airways
Increased sweating and breathing rate
Shutting down of digestive processes
Emptying of bladder
Clinically important reflexes
 Knee-jerk (also known as patellar reflex)—extension of the
lower leg in response to tapping the patellar tendon; tendon
and muscles are stretched, stimulating muscle spindles and
initiating conduction over a two-neuron reflex arc may be
 Ankle jerk (also known as Achilles reflex)—extension of the
foot in response to tapping the Achilles tendon; tendon reflex
and deep reflex mediated by two-neuron spinal arcs; centers
lie in first and second sacral segments of the cord
 Babinski reflex—extension of great toe, with or without
fanning of other toes, in response to stimulation of outer
margin of sole; present in normal infants until approximately
11⁄2 years of age
 Corneal reflex—winking in response to touching the cornea;
 Abdominal reflex—drawing in of abdominal wall in response to
stroking side of abdomen;