3. The Peripheral Nervous System
•Nervous structures outside the
brain and spinal cord
•Nerves allow the CNS to receive
information and take action
•Functional components of the PNS
•Sensory inputs and motor outputs
categorized as somatic or visceral
•Sensory inputs also classified as
general or special
4. Spinal Nerves
• 31 pairs – contain thousands
of nerve fibers
• Connect to the spinal cord
• Named for point of issue
from the spinal cord
• 8 pairs of cervical nerves
(C1–C8)
• 12 pairs of thoracic nerves
(T1–T12)
• 5 pairs of lumbar nerves
(L1–L5)
• 5 pairs of sacral nerves
(S1–S5)
• 1 pair of coccygeal nerves
(Co1)
Cauda equina (“horse’s tail”):
collection of nerve roots at
inferior end of vertebral
canal
6. Sensory Input and Motor Output
• Sensory (afferent) signals picked up by sensor
receptors, carried by nerve fibers of PNS to the
CNS
• Motor (efferent) signals are carried away from
the CNS, innervate muscles and glands
• Divided according to region they serve
• Somatic body region
• Visceral body region
• Results in four main subdivisions
• Somatic sensory
• Visceral sensory
• Somatic motor
• Visceral motor
7. PNS Afferent Division
• Afferent (sensory) division – transmits
impulses from receptors to the CNS.
• Somatic afferent fibers – carry impulses from
skin, skeletal muscles, and joints
• Visceral afferent fibers – transmit impulses from
visceral organs
8. PNS Efferent Division
• Motor (efferent) division – transmits impulses from the
CNS to effector organs. Two subdivisions:
• Somatic nervous system – provides conscious control
of skeletal muscles
• Autonomic nervous system – regulates smooth
muscle, cardiac muscle, and glands
10. Sensory
•General somatic senses – include
touch, pain, vibration, pressure,
temperature
•Proprioceptive senses – detect
stretch in tendons and muscle
provide information on body
position, orientation and
movement of body in space
•Special Senses - hearing, balance,
vision, olfaction (smell), gustation
(taste)
11. Motor
•General somatic motor
•Signals contraction of skeletal
muscles
•Under our voluntary control
•Visceral motor
•Makes up autonomic nervous
system (ANS)
•Regulates the contraction of
smooth and cardiac muscle,
controls function of visceral organs
•ANS has two divisions
•Parasympathetic
•Sympathetic
12. Sympathetic Division Organization
• Preganglionic neurons in
segments T1 to L2
• Ganglia near the
vertebral column
• Sympathetic ganglia
• Paired sympathetic
chain ganglia
• Unpaired collateral
ganglia
• Preganglionic fibers to
adrenal medullae
• Epinephrine (adrenalin)
into blood stream
13. The Autonomic Nervous System
•Effects of Sympathetic
Activation
•Generalized response in crises
•Increased alertness/energy
•Increased cardiovascular
activity
•Increased respiratory activity
•Increased muscle tone
14. Parasympathetic Division Organization
• Preganglionic
neurons in brain
stem and sacral
spinal segment
• Ganglionic neurons
(peripheral ganglia)
in or near target
organ
• Sacral fibers form
pelvic nerves
15. The Autonomic Nervous System
•Effects of Parasympathetic
Activation
•Relaxation
•Food processing
•Energy absorption
•Brief effects at specific sites
16. Basic Structural Components of the
PNS• Sensory receptors – pick up stimuli from inside or
outside the body
• Motor endings – axon terminals of motor neurons
innervate effectors (muscle fibers and glands)
• Nerves and ganglia
• Nerves – bundles of peripheral axons
• Ganglia – clusters of peripheral neuronal cell bodies
17. Nerves
• Nerves – cablelike organs
in the PNS
• Consists of numerous
axons wrapped in
connective tissue
• Endoneurium – layer of delicate
connective tissue surrounding the
axon
• Perineurium – connective tissue
wrapping surrounding a nerve
fascicle
• Nerve fascicles – groups of axons
bound into bundles
• Epineurium – whole nerve is
surrounded by tough fibrous
sheath
18. Cranial Nerves
•Attach to the brain and pass
through foramina of the skull
•Numbered from I–XII
•Cranial nerves I and II attach to the
forebrain
•All others attach to the brain stem
•Primarily serve head and neck
structures
•The vagus nerve (X) extends into
the abdomen
19. 1919
Cranial Nerves
CN # Name Attached to Foramen Function
I Olfactory Forebrain Cribriform plate Sense of smell
II Optic Forebrain Optic canal Sense of vision (sight) from
retina
III Oculomotor Midbrain
(brainstem)
Superior orbital
fissure
Motor to 4 of the 6 muscles of
eye movement (up & in);
eyelid; constriction of pupil
IV Trochlear Midbrain
(brainstem)
Superior orbital
fissure
Motor to superior oblique
muscle of eye (down & out)
V Trigeminal
V1 ophthalmic
V2 maxillary
V3 mandibular
Pons
(brainstem)
V1: superior
orbital fissure
V2: foramen
rotundum
V3: foramen
ovale
All three divisions: facial
sensation
V3 (mandibular division):
chewing also
20. 2020
VI Abducens Pons
(brainstem)
Superior orbital
fissure
Motor to lateral rectus muscle
of eye (abducts outwards)
VII Facial Pons
(brainstem)
Internal
auditory canal
Facial expression (motor)
Taste anterior 2/3 tongue
Salivary & lacrimal glands
(saliva and tears)
VIII Vestibulocochlea
r
Pons
(brainstem)
Internal
auditory
canal
Equilibrium (vestibular)
Hearing (cochlear)
IX Glossopharyngea
l
Medulla
(brainstem)
Jugular foramen Taste & touch from posterior
1/3 tongue (sour, bitter);
pharynx (throat) muscles of
swallowing; parotid gland
(saliva); senses carotid BP
X Vagus Medulla
(brainstem)
Jugular foramen Senses aortic BP, slows heart
rate, stimulates digestive
organs; larynx (vocal cords),
taste, swallowing
XI Accessory Medulla
(brainstem)
Jugular foramen Sternocleidomastoid,
trapezius, swallowing; part
joins Vagus
XII Hypoglossal Medulla
(brainstem)
Hypoglossal
canal
Innervation of tongue muscles
29. Vestibulocochlear Nerve (VIII)
•Sensory nerve of hearing and
balance
Table 14.3 (8 of 12)
Facial nerve (VII)
Vestibulocochle
ar
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
30. Glossopharyngeal Nerve (IX)
•Innervates structures of the tongue
and pharynx
Table 14.3 (9 of 12)
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
31. Vagus Nerve (X)
• A mixed sensory and motor nerve - “Wanders” into thorax
and abdomen
Table 14.3 (10 of 12)
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
32. Table 14.3 (11 of 12)
Accessory Nerve (XI)
• An accessory part of the vagus nerve -
innervates trapezius muscle
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
33. Table 14.3 (12 of 12)
Hypoglossal Nerve (XII)
• Runs inferior to the tongue - innervates
the tongue muscles
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
34. Spinal Nerves
• 31 pairs – contain thousands
of nerve fibers
• Connect to the spinal cord
• Named for point of issue
from the spinal cord
• 8 pairs of cervical nerves
(C1–C8)
• 12 pairs of thoracic nerves
(T1–T12)
• 5 pairs of lumbar nerves
(L1–L5)
• 5 pairs of sacral nerves
(S1–S5)
• 1 pair of coccygeal nerves
(Co1)
35. Spinal Nerves
• Connect to the spinal
cord by the dorsal root
and ventral root
• Dorsal root – contains
sensory fibers
• Dorsal root ganglion – of
afferent cell bodies
• Ventral root – contains
motor fibers arising
from anterior gray
column
• Branch into dorsal
ramus and ventral
ramus both contain
sensory and motor fibers
• Rami communicantes
connect to the base of
the ventral ramus and
lead to the sympathetic
chain ganglia
36. Spinal Nerves
(a)
Dorsal root
ganglion
Gray matter
White matterVentral root
Dorsal root
Dorsal and ventral
rootlets of spinal
nerveDorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Sympathetic trunk
(chain) ganglion
Spinal nerve
Rami communicantes
38. Innervation of the Back
• Dorsal rami
• Innervate back muscles
• Follow a neat, segmented pattern
• Innervate a horizontal strip of muscle and skin
• In line with emergence point from the vertebral
column
39. Innervation of the Thoracic region
• Ventral rami arranged in simple, segmented
pattern
• Intercostal nerves – supply intercostal muscles,
skin, and abdominal wall
•Each gives off lateral and anterior cutaneous
branches
41. 41
Cervical Plexus
Buried deep in the neck under the
sternocleidomastoid muscle
Formed by ventral rami of first
four cervical nerves (C 1 – 4)
Cervical plexus (C1-C4) innervates
the muscles and skin of the neck
and shoulder
most important:
Its phrenic nerve* (C3-C5) is the
sole motor supply of diaphragm:
one reason why neck injuries are
so dangerous – can be lethal
(respiratory arrest = stop
breathing)
*
43. Brachial Plexus
• Brachial plexus lies in the
neck and axilla
• Serves upper limbs and
shoulder girdle
• Arises primarily from C5-T1
• gives rise to cords
• Cords give rise to main
nerves of the upper limb
Main nerves :
• Musculocutaneous – to arm
flexors
• Median – anterior forearm
muscles and lateral palm
• Ulnar – anteromedial
muscles of forearm and
medial hand
• Axillary – to deltoid and teres
minor
• Radial – to posterior part of
limb
Figure 14.9d
47. Lumbar Plexus
• Arises from L1– L4
• Smaller branches innervate the posterior abdominal wall
and psoas muscle
• Main branches innervate the anterior thigh
48. The Sacral Plexus
• Arises from spinal nerves
L4–S4
• Often considered with the
lumbar plexus referred to as
the lumbosacral plexus
• Sciatic nerve – the largest
nerve of the sacral plexus is
actually two nerves in one
sheath
• Tibial nerve –
innervates most of the
posterior lower limb
• Common fibular
(peroneal) nerve –
innervates muscles of
the anterolateral leg
• Other branches supply
pelvic girdle (gluteus
muscles) and perineum
(pudental nerve)
