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Copyright © 2010 Pearson Education, Inc.
CHAPTER 13
PERIPHERAL NERVOUS SYSTEM
Copyright © 2010 Pearson Education, Inc.
PERIPHERAL NERVOUS SYSTEM
Organization
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Central nervous system (CNS) Peripheral nervous system (PNS)
Motor (efferent) division Sensory (afferent)
division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1 Place of the PNS in the structural organization of the nervous system.
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PERIPHERAL NERVOUS SYSTEM
Sensory Receptors
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Table 13.1 General Sensory Receptors Classified by Structure and Function (1 of 3)
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Table 13.1 General Sensory Receptors Classified by Structure and Function (2 of 3)
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Table 13.1 General Sensory Receptors Classified by Structure and Function (3 of 3)
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A receptor which responds to changes in
temperature is a…
1) mechanoreceptor
2) thermoreceptor
3) photoreceptor
4) chemoreceptor
5) nociceptor
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PERIPHERAL NERVOUS SYSTEM
Sensory Perception – CNS Integration
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Figure 13.2 Three basic levels of neural integration in sensory systems.
1
2
3
Receptor level
(sensory reception and transmission to CNS)
Circuit level
(processing in ascending pathways)
Spinal cord
Cerebellum
Reticular formation
Pons
Muscle spindle
Joint kinesthetic receptor
Free nerve endings (pain, cold, warmth)
Medulla
Perceptual level (processing in cortical sensory centers)
Motor
cortex Somatosensory
cortex
Thalamus
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Which level of sensory integration is the level
at which the reticular formation and thalamus
distribute signals to appropriate cortical
regions?
1) Circuit level
2) Receptor level
3) Perceptual level
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PERIPHERAL NERVOUS SYSTEM
NERVES: Structure
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Figure 13.3b Structure of a nerve.
Blood
vessels
Fascicle
Epineurium
Perineurium
Endoneurium
Axon
Myelin sheath
(b)
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Figure 13.3a Structure of a nerve.
Fascicle
Perineurium
Endoneurium (a)
Nerve fibers
Blood vessels
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The membrane surrounding a nerve is the...
1) endoneurium
2) epineurium
3) perineurium
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PERIPHERAL NERVOUS SYSTEM
NERVES: Classification & Location
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PERIPHERAL NERVOUS SYSTEM
Nerves: Ganglia
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A nerve is…
1) A neuron
2) A group of neuron cell bodies
3) A group of neuron axons wrapped in
connective tissue in the peripheral nervous
system
4) A group of neuron axons wrapped in
connective tissue in the central nervous
system
5) All of the above
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PERIPHERAL NERVOUS SYSTEM
Nerves: Regeneration and Repair
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Figure 13.4 Regeneration of a nerve fiber in a peripheral nerve (1 of 4).
Endoneurium
Droplets
of myelin
Fragmented
axon
Schwann cells
Site of nerve damage
The axon
becomes
fragmented at
the injury site.
1
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Figure 13.4 Regeneration of a nerve fiber in a peripheral nerve (2 of 4).
Schwann cell Macrophage Macrophages
clean out the
dead axon distal
to the injury.
2
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Figure 13.4 Regeneration of a nerve fiber in a peripheral nerve (3 of 4).
Fine axon sprouts
or filaments
Aligning Schwann cells
form regeneration tube
3 Axon sprouts,
or filaments,
grow through a
regeneration tube
formed by
Schwann cells.
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Figure 13.4 Regeneration of a nerve fiber in a peripheral nerve (4 of 4).
Schwann cell Site of new
myelin sheath
formation
4 The axon
regenerates and
a new myelin
sheath forms.
Single enlarging
axon filament
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PERIPHERAL NERVOUS SYSTEM
Cranial Nerves
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Figure 13.5a Location and function of cranial nerves.
Frontal lobe
Temporal lobe
Infundibulum
Facial
nerve (VII)
Vestibulo-
cochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
(a)
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Optic chiasma
Optic nerve
(II)
Optic tract Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Abducens
nerve (VI)
Cerebellum
Medulla oblongata
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Figure 13.5b Location and function of cranial nerves.
*PS = parasympathetic (b)
Cranial nerves
I – VI
I
II
III
IV
V
VI
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
No
Yes
Yes
Yes
Yes
No
No
Yes
No
No
No
Cranial nerves
VII – XII
Sensory
function
Motor
function
PS*
fibers
Sensory
function
Motor
function
PS*
fibers
VII
VIII
IX
X
XI
XII
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Yes (taste)
Yes (hearing
and balance)
Yes (taste)
Yes (taste)
No
No
Yes
Some
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
No
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Cranial nerve I is also known as the…
1) Hypoglossal nerve
2) Olfactory nerve
3) Optic nerve
4) Vagus nerve
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PERIPHERAL NERVOUS SYSTEM
Spinal Nerves
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Figure 13.6 Spinal nerves.
Cervical nerves
C1 – C8
Thoracic nerves
T1 – T12
Lumbar nerves
L1 – L5
Sacral nerves S1 – S5
Coccygeal nerve Co1
Cervical plexus
Intercostal nerves
Cervical enlargement
Lumbar enlargement
Cauda equina
Brachial plexus
Lumbar plexus
Sacral plexus
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PERIPHERAL NERVOUS SYSTEM
Spinal Nerves: Branches
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Figure 13.7a Formation of spinal nerves and rami distribution.
Dorsal root ganglion
Gray matter
White matter
Ventral root
Dorsal root
Dorsal and ventral rootlets of spinal nerve
Dorsal ramus of spinal nerve
Ventral ramus of spinal nerve
Sympathetic trunk ganglion
Spinal nerve
Rami communicantes
(a) Anterior view showing spinal cord, associated nerves, and vertebrae.
The dorsal and ventral roots arise medially as rootlets and join
laterally to form the spinal nerve.
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Figure 13.7b Formation of spinal nerves and rami distribution.
Dorsal ramus
Ventral ramus
Intercostal nerve
Spinal nerve
Rami communicantes
Dorsal root ganglion Dorsal root Ventral root
Sympathetic trunk ganglion
Sternum
(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
Branches of intercostal
nerve
• Lateral cutaneous • Anterior cutaneous
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True or false: information only flows toward
the spinal cord in a dorsal ramus.
1) True
2) False
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PERIPHERAL NERVOUS SYSTEM
Spinal Nerves: Plexuses (Plexi?)
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Figure 13.8 The cervical plexus.
Hypoglossal nerve (XII)
C1
C2
C3
C4
C5
Segmental
branches
Lesser occipital nerve Greater auricular nerve
Ansa cervicalis
Phrenic nerve
Supraclavicular
nerves
Accessory nerve (XI)
Transverse cervical nerve
Ventral
rami:
Ventral rami
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Figure 13.9a The brachial plexus.
Upper
Middle Trunks
Lower
Roots (ventral rami):
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneous
nerves of the arm
and forearm
Long thoracic
Medial pectoral
Lateral pectoral
Nerve to subclavius
Suprascapular
Dorsal scapular
Posterior divisions
Anterior
divisions
Lateral
Posterior Cords
Medial
Axillary
Musculo- cutaneous
Radial
Median
Ulnar
Posterior
divisions
Trunks Roots
C4
C5
C6
C7
C8
T1
(a) Roots (rami C5 – T
1), trunks, divisions, and cords
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Figure 13.9b The brachial plexus.
Musculocutaneous nerve Lateral
cord
Posterior cord
Medial cord
Radial nerve
Ulnar nerve
Axillary nerve
Biceps brachii
Coracobrachialis
Median nerve
Radial nerve branches to triceps
(b) Cadaver photo
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Figure 13.9c The brachial plexus.
Median nerve
Musculocutaneous nerve
Radial nerve
Humerus
Ulna
Ulnar nerve
Median nerve
Radius
Radial nerve (superficial branch)
Superficial branch of ulnar nerve Dorsal branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Digital branch
(c) The major nerves of the upper limb
Axillary
nerve Anterior divisions
Posterior divisions
Trunks Roots
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Figure 13.9d The brachial plexus.
Anterior
divisions
(d) Flowchart summarizing relationships within the
brachial plexus
Major terminal
branches
(peripheral nerves) Cords Divisions Trunks
Roots
(ventral
rami)
Musculocutaneous
Median
Ulnar
Radial
Axillary
Anterior
Posterior
Anterior
Posterior
Posterior
Anterior
Upper
Middle
Lower
Lateral
Medial
Posterior
Posterior
divisions
Trunks Roots
C5
C6
C7
C8
T1
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Figure 13.10 The lumbar plexus.
(a) Ventral rami and major branches
of the lumbar plexus
Iliohypogastric
L1
L2
L3
L4
L5
Ilioinguinal
Genitofemoral
Lateral femoral
cutaneous
Obturator
Femoral
Lumbosacral
trunk
Lateral femoral
cutaneous
Anterior femoral
cutaneous
Saphenous
Obturator
Iliohypogastric
Ilioinguinal
Femoral
Ventral rami Ventral
rami:
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
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Figure 13.10a The lumbar plexus.
(a) Ventral rami and major branches
of the lumbar plexus
Iliohypogastric
L1
L2
L3
L4
L5
Ilioinguinal
Genitofemoral
Lateral femoral
cutaneous
Obturator
Femoral
Lumbosacral
trunk
Ventral rami Ventral
rami:
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Figure 13.10b The lumbar plexus.
Lateral femoral cutaneous
Anterior femoral cutaneous
Saphenous
Obturator
Iliohypogastric
Ilioinguinal
Femoral
(b) Distribution of the major
nerves from the lumbar
plexus to the lower limb
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Figure 13.11a The sacral plexus.
Superior gluteal
Lumbosacral trunk
Inferior gluteal
Common fibular
Tibial
Posterior femoral cutaneous
Pudendal
Sciatic
(a) Ventral rami and major branches
of the sacral plexus
L4
L5
S1
S2
S3
S4
S5
Co1
Ventral rami Ventral rami:
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Figure 13.11b The sacral plexus.
Superior gluteal
Inferior gluteal
Common fibular
Deep fibular
Superficial fibular
Plantar branches
Tibial
Sural (cut)
Posterior femoral cutaneous
Pudendal
Sciatic
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
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Figure 13.11c The sacral plexus.
Pudendal nerve
Gluteus maximus (medial portion removed)
Piriformis
Inferior gluteal nerve
Greater trochanter of femur
Common fibular nerve
Tibial nerve
Sciatic nerve
Posterior femoral cutaneous nerve
Ischial tuberosity
(c) Cadaver photo
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PERIPHERAL NERVOUS SYSTEM
Spinal Nerves: Dermatomes
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Figure 13.12 Map of dermatomes.
C2
C3
C4
C5
T1
T2
T2
T3
T4
T5
C6
C8
C7 C7
C6
T6
T7
T8
T9
T10
T11
T12
L1
S2
S3
L1
L2
L3
L4
L5
L2
L3
L4
L5
S1
C5
C6
C8
T2
C5
C6
S1
(a) Anterior
view
C2
C3
C4
C5
C6
C7
C8
C8 C8
C7 C7
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2 L3
S1
(b) Posterior
view
L5 S2
S1
S1
S3
S2 S1 S2
S4
S5
L5 L5
L4
L5 L5
L4
C6 C6
C5
L4
L3
L2
L1
L4
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True or false: Pain felt on the surface of a body
region is always related to skin problems.
1) True
2) False
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PERIPHERAL NERVOUS SYSTEM
MOTOR ENDINGS
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PERIPHERAL NERVOUS SYSTEM
MOTOR INTEGRATION
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Figure 13.13 Hierarchy of motor control.
Feedback
Reflex activity Motor output
Sensory input
(a) Levels of motor control and their interactions
Precommand Level
(highest)
• Cerebellum and basal nuclei • Programs and instructions (modified by feedback)
Projection Level (middle) • Motor cortex (pyramidal system) and brain stem nuclei (vestibular, red, reticular formation, etc.)
• Convey instructions to spinal cord motor neurons and send a copy of that information to higher levels
Segmental Level (lowest)
• Spinal cord • Contains central pattern generators (CPGs)
Internal feedback
(b) Structures involved
Precommand level
• Cerebellum • Basal nuclei
Projection level
• Primary motor cortex • Brain stem nuclei
Segmental level
• Spinal cord
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PERIPHERAL NERVOUS SYSTEM
REFLEX ARC
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Figure 13.14 The five basic components of all reflex arcs.
Receptor
Sensory neuron
Integration center
Motor neuron
Effector
Spinal cord
(in cross section)
Interneuron
Stimulus
Skin
1
2
3
4
5
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Figure 13.15 Anatomy of the muscle spindle and Golgi tendon organ.
Secondary sensory
endings (type II fiber)
Efferent (motor)
fiber to muscle spindle
Primary sensory
endings (type Ia
fiber)
Connective
tissue capsule
Muscle spindle
Tendon
Sensory fiber
Golgi tendon
organ
Efferent (motor)
fiber to extrafusal
muscle fibers
Extrafusal muscle
fiber
Intrafusal muscle
fibers
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Figure 13.16 Operation of the muscle spindle.
(a) Unstretched
muscle. Action
potentials (APs)
are generated at
a constant rate in
the associated
sensory (la) fiber.
Muscle
spindle
Intrafusal
muscle fiber
Primary sensory (la) nerve fiber
Extrafusal
muscle fiber
Time
(b) Stretched
muscle. Stretching
activates the muscle
spindle, increasing the rate of APs.
Time
(d) - Coactivation.
Both extrafusal and
intrafusal muscle
fibers contract.
Muscle spindle
tension is main-
tained and it can
still signal changes
in length.
Time
(c) Only motor
neurons activated.
Only the extrafusal
muscle fibers contract.
The muscle spindle
becomes slack and no
APs are fired. It is
unable to signal further length changes.
Time
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Figure 13.17 The Stretch Reflex (1 of 2)
1 When muscle spindles are activated by stretch, the associated sensory neurons (blue) transmit afferent impulses at higher frequency to the spinal cord.
2 The sensory neurons synapse directly with alpha motor neurons (red), which excite extrafusal fibers of the stretched muscle. Afferent fibers also synapse with interneurons (green) that inhibit motor neurons (purple) controlling antagonistic muscles.
The events by which muscle stretch is damped
3a Efferent impulses of alpha motor neurons cause the stretched muscle to contract, which resists or reverses the stretch.
3b Efferent impulses of alpha motor neurons to antagonist muscles are reduced (reciprocal inhibition).
Initial stimulus
(muscle stretch)
Cell body of sensory neuron
Sensory neuron
Muscle spindle
Antagonist muscle
Spinal cord
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Figure 13.17 The Stretch Reflex (2 of 2)
The patellar (knee-jerk) reflex – a specific example of a stretch reflex
Muscle
spindle
Quadriceps
(extensors)
Hamstrings
(flexors)
Patella
Patellar
ligament
Spinal cord
(L2 – L4)
3a
2
1
3b 3b
1 Tapping the patellar ligament excites
muscle spindles in the quadriceps muscle.
2
3a The motor neurons (red) send
activating impulses to the quadriceps
causing it to contract, extending the
knee.
Afferent impulses (blue) travel to the
spinal cord, where synapses occur with
motor neurons and interneurons.
3b The interneurons (green) make
inhibitory synapses with ventral horn
neurons (purple) that prevent the
antagonist muscles (hamstrings) from
resisting the contraction of the
quadriceps.
Excitatory synapse Inhibitory synapse –
+
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Figure 13.19 The crossed-extensor reflex.
Afferent
fiber
Efferent
fibers
Extensor
inhibited
Flexor
stimulated
Site of stimulus: a noxious stimulus causes a flexor
reflex on the same side, withdrawing that limb.
Site of reciprocal
activation: At the same time, the extensor muscles on the opposite side are activated.
Arm
movements
Interneurons
Efferent
fibers
Flexor inhibited
Extensor stimulated
+ Excitatory synapse
– Inhibitory synapse
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True or false: The flexor-crossed extensor
reflex involves multiple integration neurons.
1) True
2) False