Download Chapter 12 - Las Positas College

PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
12
HUMAN
ANATOMY
fifth edition
MARIEB | MALLATT | WILHELM
PART 1
Fundamentals
of the
Nervous
System and
Nervous
Tissue
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Nervous System


Master control and communication system
Has three overlapping functions
 Sensory receptors monitor changes inside and
outside the body
 Change – a stimulus
 Gathered information – sensory input
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Nervous System

Processes and interprets sensory input
 Makes decisions – integration

Dictates a response by activating effector organs
 Response – motor output
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Basic Divisions of the Nervous System

Central nervous system (CNS)
 Brain and spinal cord
 Integrating and command center
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Basic Divisions of the Nervous System

Peripheral nervous system (PNS)
 Outside the CNS
 Consists of nerves extending from brain and spinal
cord
 Cranial nerves
 Spinal nerves
 Peripheral nerves link all regions of the body to the
CNS
 Ganglia are clusters of neuronal cell bodies
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Basic Divisions of the Nervous System
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.2
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
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Sensory Input and Motor Output

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
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Types of Sensory and Motor Information
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Figure 12.3
Basic Divisions of the Nervous System

Somatic sensory
 General somatic senses – receptors are widely
spread
 Touch
 Pain
 Vibration
 Pressure
 Temperature
(receptors discussed in Chapter 14)
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Basic Divisions of the Nervous System

Somatic sensory (continued)
 Proprioceptive senses – detect stretch in tendons
and muscle
 Body sense – position and movement of body in
space
 Special somatic senses (Chapter 16)
 Hearing
 Balance
 Vision
 Smell
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Basic Divisions of the Nervous System

Visceral sensory
 General visceral senses – stretch, pain, temperature,
nausea, and hunger
 Widely felt in digestive and urinary tracts, and
reproductive organs
 Special visceral senses
 Taste
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Basic Divisions of the Nervous System

Somatic motor
 General somatic motor – signals contraction of
skeletal muscles
 Under our voluntary control
 Often called “voluntary nervous system”
 Branchial motor
 Typical skeletal muscle derived from somitomeres
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Basic Divisions of the Nervous System

Visceral motor
 Regulates the contraction of smooth and cardiac
muscle
 Makes up autonomic nervous system
 Controls function of visceral organs
 Often called “involuntary nervous system”
 Autonomic nervous system (Chapter 15)
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Nervous Tissue

Cells are densely packed and intertwined
 Two main cell types
 Neurons – transmit electrical signals
 Support cells (neuroglial cells in CNS)
 Nonexcitable
 Surround and wrap neurons
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The Neuron

The human body contains billions of neurons
 Basic structural unit of the nervous system
 Specialized cells conduct electrical impulses along
the plasma membrane
 Nerve impulse (action potential)
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The Neuron

Other special characteristics
 Longevity – can live and function for a lifetime
 Do not divide – fetal neurons lose their ability to
undergo mitosis; neural stem cells are an exception
 High metabolic rate – require abundant oxygen
and glucose
 Neurons die after 5 minutes without oxygen
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The Cell Body

Cell body (soma)
 Perikaryon – around nucleus
 Size of cell body varies from 5–140µm
 Contains usual organelles plus other structures
 Chromatophilic bodies (Nissl bodies)
 Clusters of rough ER and free ribosomes
 Stain darkly and renew membranes of the
cell
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The Cell Body

Neurofibrils – bundles of intermediate filaments
 Form a network between chromatophilic bodies
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The Cell Body

Most neuronal cell bodies
 Located within the CNS
 Protected by bones of the skull and vertebral
column

Ganglia – clusters of cell bodies
 Lie along nerves in the PNS
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Structure of a Typical Large Neuron
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Figure 12.4
Neuron Processes

Dendrites
 Extensively branching from the cell body
 Transmit electrical signals toward the cell body
 Chromatophilic bodies – only extend into the
basal part of dendrites and to the base of the axon
hillock
 Function as receptive sites for receiving signals
from other neurons
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Neuron Processes

Axons
 Neuron has only one
 Impulse generator and conductor
 Transmits impulses away from the cell body
 Chromatophilic bodies are absent
 No protein synthesis in axon
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Neuron Processes

Axons (continued)
 Neurofilaments, actin microfilaments, and
microtubules
 Provide strength along length of axon
 Aid in the transport of substances to and from the
cell body
 Axonal transport
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Neuron Processes

Axons
 Branches along length are infrequent
 Axon collaterals
 Multiple branches at end of axon
 Terminal branches (telodendria)
 End in knobs called axon terminals
(also called end bulbs or boutons)
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Neuron Processes

Nerve impulse
 Generated at the initial segment of the axon
 Conducted along the axon
 Releases neurotransmitters at axon terminals
 Neurotransmitters – excite or inhibit neurons
 Neuron receives and sends signals
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Synapses



Site at which neurons communicate
Signals pass across synapse in one direction
Presynaptic neuron
 Conducts signal toward a synapse

Postsynaptic neuron
 Transmits electrical activity away from a synapse
PLAY
Synapse
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Two Neurons Communicating at a Synapse
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Figure 12.6
Types of Synapses

Axodendritic
 Between axon terminals of one neuron and
dendrites of another
 Most common type of synapse

Axosomatic

Axoaxonic, dendrodendritic, and
dendrosomatic
 Between axons and neuronal cell bodies
 Uncommon types of synapses
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Some Important Types of Synapses
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Figure 12.7
Synapses



Elaborate cell junctions
Axodendritic synapses – representative type
Synaptic vesicles on presynaptic side
 Membrane-bound sacs containing
neurotransmitters
 Mitochondria abundant in axon terminals

Synaptic cleft
 Separates the plasma membrane of the two neurons
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Structure of a Synapses
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Figure 12.8a, b
Signals Carried by Neurons


Plasma membranes of neurons conduct electrical
signals
Resting neuron – membrane is polarized
 Inner, cytoplasmic side is negatively charged

Stimulation of the neuron  depolarization
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Signals Carried by Neurons
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Figure 12.9a, b
Signals Carried by Neurons

Strong stimulus applied to the axon triggers
 Nerve impulse/action potential



Membrane becomes negative externally
Impulse travels the length of the axon
Membrane repolarizes itself
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Signals Carried by Neurons
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Figure 12.9c–d
Synaptic Potentials

Excitatory synapses
 Neurotransmitters alter the permeability of the
postsynaptic membrane
 Leads to an inflow of positive ions
 Depolarizes the postsynaptic membrane
 Drives the postsynaptic neuron toward impulse
generation
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Synaptic Potentials

Inhibitory synapses
 The external surface of the postsynaptic membrane
becomes more positive
 Reduces the ability of the postsynaptic neuron to
generate an action potential
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
12
HUMAN
ANATOMY
fifth edition
MARIEB | MALLATT | WILHELM
PART 2
Fundamentals
of the
Nervous
System and
Nervous
Tissue
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Classification of Neurons

Structural classification
 Multipolar – possess more than two processes
 Numerous dendrites and one axon
 Bipolar – possess two processes
 Rare neurons
 Found in some special sensory organs
 Unipolar (pseudounipolar) – possess one short,
single process
 Start as bipolar neurons during development
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Neurons Classified by Structure
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Figure 12.10a
Neurons Classified by Structure
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Figure 12.10b
Neurons Classified by Structure
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Figure 12.10c
Functional Classification of Neurons

Functional classification is
 According to the direction the nerve impulse
travels

Sensory (afferent) neurons
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Functional Classification of Neurons

Transmit impulses toward the CNS
 Virtually all are unipolar neurons
 Cell bodies in ganglia outside the CNS
 Short, single process divides into
 The central process – runs centrally into the
CNS
 The peripheral process – extends
peripherally to the receptors
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Functional Classification of Neurons

Motor (efferent) neurons
 Carry impulses away from the CNS to effector
organs
 Most motor neurons are multipolar
 Cell bodies are within the CNS
 Form junctions with effector cells

Interneurons (association neurons) – most are
multipolar
 Lie between motor and sensory neurons
 Confined to the CNS
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Neurons Classified by Function
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Figure 12.11
Supporting Cells

Six types of supporting cells
 Four in the CNS
 Two in the PNS


Provide supportive functions for neurons
Cover nonsynaptic regions of the neurons
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Neuroglial in the CNS

Neuroglia
 Glial cells have branching processes and a central
cell body
 Outnumber neurons 10 to 1
 Make up half the mass of the brain
 Can divide throughout life
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Neuroglia in the CNS

Astrocytes are the most abundant glial cell type
 Sense when neurons release glutamate
 Extract blood sugar from capillaries for energy
 Take up and release ions in order to control
environment around neurons
 Involved in synapse formation in developing neural
tissue
 Produce molecules necessary for neuronal growth
(BDTF)
 Propagate calcium signals involved with memory
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Neuroglia in the CNS
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Figure 12.12a
Neuroglia in the CNS

Microglia –
smallest and least
abundant glial cell
 Phagocytes – the
macrophages
of the CNS
 Engulf invading
microorganisms
and dead neurons
 Derive from blood
cells called
monocytes
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Figure 12.12b
Neuroglia in the CNS

Ependymal cells
 Line the central cavity of the spinal cord and brain
 Bear cilia – help circulate the cerebrospinal fluid

Oligodendrocytes – have few branches
 Wrap their cell processes around axons in CNS
 Produce myelin sheaths
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Neuroglia in the CNS
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Figure 12.12c, d
Neuroglia in the PNS


Satellite cells – surround neuron cell bodies
within ganglia
Schwann cells (neurolemmocytes) – surround
axons in the PNS
 Form myelin sheath around axons of the PNS
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.13
PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
12
HUMAN
ANATOMY
fifth edition
MARIEB | MALLATT | WILHELM
PART 3
Fundamentals
of the
Nervous
System and
Nervous
Tissue
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Myelin Sheaths



Segmented structures composed of the lipoprotein
myelin
Surround thicker axons
Form an insulating layer
 Prevent leakage of electrical current

Increase the speed of impulse conduction
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Myelin Sheaths in the PNS



Formed by Schwann cells (neurolemmacytes)
Develop during fetal period and in the first year of
postnatal life
Schwann cells wrap in concentric layers around the
axon
 Cover the axon in a tightly packed coil of
membranes

Neurilemma
 Material external to myelin layers
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Myelin Sheaths in the PNS
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Figure 12.14a, b
Myelin Sheaths in the PNS
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Figure 12.14c, d
Myelin Sheaths in the PNS
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Figure 12.15a
Myelin Sheaths in the PNS

Nodes of Ranvier – gaps along axon
 Thick axons are myelinated
 Thin axons are unmyelinated
 Conduct impulses more slowly
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Myelin Sheaths in the CNS

Oligodendrocytes form the myelin sheaths in the
CNS
 Have multiple processes
 Coil around several different axons
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Figure 12.15b
Gray and White Matter in the CNS

Gray matter
 Is gray-colored and surrounds hollow central
cavities of the CNS
 Forms H-shaped region in the spinal cord
 Dorsal half contains cell bodies of interneurons
 Ventral half contains cell bodies of motor neurons
 Primarily composed of neuronal cell bodies,
dendrites, unmyelinated axons
 Surrounds white matter of CNS in cerebral cortex
and cerebellum
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Gray and White Matter in the CNS

White matter
 Lies external to the gray matter of the CNS
 Composed of myelinated axons
 Consists of axons passing between specific regions
of the CNS
 Tracts are bundles of axons traveling to similar
destinations
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Nerves

Nerves – cablelike organs in the PNS
 Consists of numerous axons wrapped in connective
tissue
 Axon is surrounded by Schwann cells

You see many nerves in lab
 Nerves of Brachial Plexus
 Radial, axillary, median, musculocutaneous, ulnar
 Nerves of lumbosacral plexus
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Nerves


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
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Structure of a Nerve
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Figure 12.16a
Integration Between the PNS and CNS


The CNS and PNS are functionally interrelated
Nerves of the PNS
 Information pathways to and from body periphery
 Afferent PNS fibers respond to sensory stimuli
 Efferent PNS fibers transmit motor stimuli from
CNS to muscles and glands
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Integration Between the PNS and CNS

Nerves of the CNS
 Composed on interneurons that
 Process and receive sensory information
 Direct information to specific CNS regions
 Initiate appropriate motor responses
 Transport information from one area of the CNS to
another
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Reflex Arcs

Reflex arcs – simple chains of neurons
 Explain reflex behaviors
 Determine structural plan of the nervous system
 Responsible for reflexes
 Rapid, autonomic motor responses
 Can be visceral or somatic
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Five Essential Components to the Reflex Arc



Receptor – site where stimulus acts
Sensory neuron – transmits afferent impulses to
the CNS
Integration center – consists of one or more
synapses in the CNS
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Five Essential Components to the Reflex Arc


Motor neuron – conducts efferent impulses from
integration center to an effector
Effector – muscle or gland cell
 Responds to efferent impulses
 Contracting or secreting
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Five Essential Components to the Reflex Arc
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Figure 12.17
Types of Reflexes

Monosynaptic reflex
 Simplest of all reflexes
 Just one synapse
 The fastest of all reflexes
 Knee-jerk reflex
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Types of Reflexes

Polysynaptic reflex
 More common type of reflex
 Most have a single interneuron between the sensory
and motor neuron
 Withdrawal reflexes
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Types of Reflexes
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Figure 12.18a, b
Simplified Design of the Nervous System

Three-neuron reflex arcs
 Basis of the structural plan of the nervous system
 Similar reflexes are associated with the brain
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Simplified Design of the Nervous System

Sensory neurons – located dorsally
 Cell bodies outside the CNS in sensory ganglia
 Central processes enter dorsal aspect of the spinal
cord

Motor neurons – located ventrally
 Axons exit the ventral aspect of the spinal cord
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Simplified Design of the Nervous System

Interneurons – located centrally
 Synapse with sensory neurons
 Interneurons are neurons confined to CNS
 Long chains of interneurons between sensory and
motor neurons
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Simplified Design of the Nervous System
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Figure 12.19
Neuronal Circuits



Diverging circuit – one presynaptic neuron
synapses with several other neurons (divergence)
Converging circuit – many neurons synapse on a
single postsynaptic neuron (convergence)
Reverberating circuit – circuit that receives
feedback via a collateral axon from a neuron in the
circuit
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Neuronal Circuits
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Figure 12.20
Input Processing – not in notes

Serial processing
 Neurons pass a signal to a specific destination
along a single pathway from one to another


Parallel processing
Input is delivered along many pathways; a single
sensory stimulus results in multiple perceptions
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Neural Processing
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Figure 12.21
Disorders of the Nervous System

Multiple sclerosis
 Common cause of neural disability
 An autoimmune disease
 Immune system attacks the myelin around axons in
the CNS
 Varies widely in intensity among those affected
 More women than men are affected
 When men are affected disease develops quicker and
is more devastating
 Cause is incompletely understood
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Nervous Tissue Throughout Life

Nervous system develops from the dorsal
ectoderm
 Invaginates to form the neural tube and neural crest
 Neural tube walls begin as neuroepithelial cells
 These cells divide and become neuroblasts
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Nervous Tissue Throughout Life
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Figure 12.22
Neuronal Regeneration


Neural injuries may cause permanent dysfunction
If axons alone are destroyed, cells bodies often
survive and the axons may regenerate
 PNS – macrophages invade and destroy axon distal
to the injury
 Axon filaments grow peripherally from injured site
 Partial recovery is sometimes possible
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Neuronal Regeneration
 CNS – neuroglia never form bands to guide regrowing axons and may hinder axon growth with
growth-inhibiting chemicals
 No effective regeneration after injury to the spinal
cord and brain
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Regeneration of the Peripheral Nerve Fiber
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Figure 12.23