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Chapter 10
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2
Hole’s Human Anatomy
and Physiology
Twelfth Edition
Shier w Butler w Lewis
Chapter
10
Nervous System I: Basic
Structure and Function
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3
10.1: Introduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
• Cell types in neural tissue:
• Neurons
• Neuroglial cells (also
known as neuroglia, glia,
and glial cells)
Cell body
Nuclei of
neuroglia
Axon
4
© Ed Reschke
Divisions of the
Nervous System
• Central Nervous System (CNS)
• Brain
• Spinal cord
• Peripheral Nervous System (PNS)
• Cranial nerves
• Spinal nerves
5
Divisions of Peripheral
Nervous System
• Sensory Division
• Picks up sensory information and delivers it to the CNS
• Motor Division
• Carries information to muscles and glands
• Divisions of the Motor Division:
• Somatic – carries information to skeletal muscle
• Autonomic – carries information to smooth muscle,
cardiac muscle, and glands
6
Divisions Nervous System
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Central Nervous System
(brain and spinal cord)
Brain
Peripheral Nervous System
(cranial and spinal nerves)
Cranial
nerves
Sensory division
Spinal
cord
Sensory receptors
Spinal
nerves
Motor division
Somatic
Nervous
System
Skeletal muscle
Autonomic
Nervous
System
Smooth muscle
Cardiac muscle
Glands
7
(a)
(b)
10.1 Clinical Application
Migraine
8
10.2: General Functions of
the Nervous System
• The three general functions of the nervous system:
• Receiving stimuli = sensory function
• Deciding about stimuli = integrative function
• Reacting to stimuli = motor function
9
Functions of Nervous System
• Sensory Function
• Sensory receptors gather information
• Information is carried to the CNS
• Integrative Function
• Sensory information used to create:
• Sensations
• Memory
• Thoughts
• Decisions
• Motor Function
• Decisions are acted upon
• Impulses are carried to effectors
10
10.3: Description of Cells of
the Nervous System
• Neurons vary in size and shape
• They may differ in length and size of their axons and dendrites
• Neurons share certain features:
• Dendrites
• A cell body
• An axon
11
Neuron Structure
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Chromatophilic
substance
(Nissl bodies)
Dendrites
Cell body
Nucleus
Nucleolus
Axonal
hillock
Synaptic knob of
axon terminal
Impulse
Neurofibrils
Axon
Nodes of Ranvier
Myelin (cut)
Axon
Schwann
cell
Nucleus of
Schwann cell
Portion of a
collateral
12
Myelination of Axons
• White Matter
• Contains myelinated
axons
• Considered fiber tracts
• Gray Matter
• Contains unmyelinated
structures
• Cell bodies, dendrites
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Dendrite
Unmyelinated
region of axon
Myelinated region of axon
Node of Ranvier
Axon
(a)
Neuron
Neuron
cell body nucleus
Enveloping
Schwann cell
Schwann
cell nucleus
Longitudinal
groove
(c)
Unmyelinated
axon
13
10.2 Clinical Application
Multiple Sclerosis
14
10.4: Classification of Neurons
and Neuroglia
• Neurons vary in function
• They can be sensory, motor, or integrative neurons
• Neurons vary in size and shape, and in the number of axons
and dendrites that they may have
• Due to structural differences, neurons can be classified into
three (3) major groups:
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
15
Classification of Neurons:
Structural Differences
• Bipolar neurons
• Two processes
• Eyes, ears, nose
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Dendrites
• Unipolar neurons
• One process
• Ganglia of PNS
• Sensory
• Multipolar neurons
• 99% of neurons
• Many processes
• Most neurons of
CNS
Peripheral
process
Axon
Direction
of impulse
Central
process
Axon
(a) Multipolar
Axon
(b) Bipolar
(c) Unipolar
16
Classification of Neurons:
Functional Differences
• Sensory Neurons
• Afferent
• Carry impulse to CNS
• Most are unipolar
• Some are bipolar
• Interneurons
• Link neurons
• Aka association neurons
or internuncial neurons
• Multipolar
• Located in CNS
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Central nervous system
Peripheral nervous system
Cell body
Dendrites
Sensory
receptor
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory (afferent) neuron
Interneurons
• Motor Neurons
• Multipolar
• Carry impulses away from CNS
• Carry impulses to effectors
Motor (efferent) neuron
Axon
Effector
(muscle or gland)
Axon
Axon
terminal
17
Types of Neuroglial Cells
in the PNS
1) Schwann Cells
• Produce myelin found on peripheral myelinated neurons
• Speed up neurotransmission
2) Satellite Cells
• Support clusters of neuron cell bodies (ganglia)
18
Types of Neuroglial Cells
in the CNS
1) Microglia
• CNS
• Phagocytic cell
3) Oligodendrocytes
• CNS
• Myelinating cell
2) Astrocytes
4) Ependyma or ependymal
• CNS
• CNS
• Scar tissue
• Ciliated
• Mop up excess ions, etc.
• Line central canal of spinal
• Induce synapse formation
cord
• Connect neurons to blood vessels • Line ventricles of brain
• Part of Blood Brain Barrier
19
Types of Neuroglial Cells
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Fluid-filled cavity
of the brain or
spinal cord
Neuron
Ependymal
cell
Oligodendrocyte
Astrocyte
Microglial cell
Axon
Capillary
Myelin
sheath (cut)
Node of
Ranvier
20
Regeneration of A Nerve Axon
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Skeletal
muscle fiber
Motor neuron
cell body
Changes
over time
Site of injury
Schwann cells
Axon
(a)
Distal portion of
axon degenerates
(b)
Proximal end of injured axon
regenerates into tube of sheath cells
(c)
Schwann cells
degenerate
(d)
Schwann cells
proliferate
(e)
Former connection
reestablished
21
10.5: The Synapse
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• Nerve impulses pass
from neuron to neuron at
synapses, moving from a
pre-synaptic neuron to a
post-synaptic neuron.
Synaptic
cleft
Impulse
Dendrites
Axon of
presynaptic
neuron
Axon hillock of
Postsynaptic neuron
Axon of
presynaptic
neuron
Impulse
Cell body of Impulse
postsynaptic
neuron
22
Synaptic Transmission
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Direction of
nerve impulse
• Neurotransmitters are
released when impulse
reaches synaptic knob
Axon
Ca+2
Synaptic knob
Synaptic
vesicles
Presynaptic neuron
Ca+2
Cell body or dendrite
of postsynaptic neuron
Mitochondrion
Ca+2
Synaptic
vesicle
Vesicle releasing
neurotransmitter
Axon
membrane
Neurotransmitter
Synaptic cleft
Polarized
membrane
Depolarized
membrane
(a)
23
Animation: Chemical Synapse
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24
10.6: Cell Membrane Potential
• A cell membrane is usually electrically charged, or
polarized, so that the inside of the membrane is negatively
charged with respect to the outside of the membrane (which is
then positively charged).
• This is as a result of unequal distribution of ions on the
inside and the outside of the membrane.
25
Distribution of Ions
• Potassium (K+) ions are the major intracellular positive ions (cations).
• Sodium (Na+) ions are the major extracellular positive ions (cations).
• This distribution is largely created by the Sodium/Potassium Pump
(Na+/K+ pump).
• This pump actively transports 3 sodium ions out of the cell and 2
potassium ions into the cell.
26
Resting Potential
• Resting Membrane Potential
(RMP):
• 70 mV difference from
inside to outside of cell
• It is a polarized
membrane
• Inside of cell is negative
relative to the outside of
the cell
• RMP = -70 mV
• Due to distribution of
ions inside vs. outside
• Na+/K+ pump restores
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High Na+
Low K+
Low Na+
Impermeant
anions
High K+
Cell body
Axon Axon terminal
+
–
(a)
+
–
+
–
+–
– –
+ +
– –
+ +
+
–
–
+
+
–
+
–
–
–
+
+
–70 mV
+
–
–
+
(b)
+
+
– + –
+ +
– Na
– Low
+
Na+ Pump
–
–
K+
+
–
Low K++ – High K+–
+ +
High Na+
+
–
–
–
+
+
–70 mV
+
–
–
+
+
–
–
+
(c)
27
+
–
–
+
Local Potential Changes
• Caused by various stimuli:
• Temperature changes
Gate-like mechanism
• Light
• Pressure
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Protein
Cell
membrane
(a) Channel closed
Fatty acid
tail
Phosphate
head
(b) Channel open
• Environmental changes affect the membrane
potential by opening a gated ion channel
• Channels are 1) chemically gated, 2) voltage gated,
or 3) mechanically gated
28
Local Potential Changes
• If membrane potential becomes more negative, it has hyperpolarized
• If membrane potential becomes less negative, it has depolarized
• Graded (or proportional) to intensity of stimulation reaching
threshold potential
• Reaching threshold potential results in a nerve impulse, starting an
action potential
29
Local Potential Changes
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Na+
Na+
–62 mV
Neurotransmitter
(a)
Chemically-gated
Na+ channel
Presynaptic
neuron
Voltage-gated
Na+ channel
Trigger zone (axon hillock)
Na+
Na+
Na+
Na+ Na+
–55 mV
30
(b)
Action Potentials
• At rest, the membrane is
polarized (RMP = -70)
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Na+
• Threshold stimulus
reached (-55)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
Na+
–0
–70
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
(a)
• Sodium channels open
and membrane
depolarizes (toward 0)
K+
Na+
Na+
K+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
K+
K+
–0
K+
Threshold
stimulus K+
K+
Na+
Na+ channels open
K+ channels closed
K+
Na+
Na+
–70
• Potassium leaves
cytoplasm and
membrane repolarizes
(+30)
• Brief period of
hyperpolarization (-90)
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Region of depolarization
(b)
K+
K+
Na+
K+
Na+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
Na+
Na+
Na+
K+
K+
K+
K+
K+
K+
K+
K+
Na+
Na+
Region of repolarization
(c)
Na+
Na+
Na+
Na+
Na+
–0
K+ channels open
Na+ channels closed
–70
Na+
31
Action Potentials
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+40
Membrane potential (millivolts)
Action potential
+20
0
–20
Resting potential
reestablished
–40
Resting
potential
–60
–80
Hyperpolarization
0
1
2
3
4
5
Milliseconds
6
7
8
32
Action Potentials
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Region of
action potential
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
–
–
–
–
–
–
–
–
–
–
–
–
+
+
+
(a)
+
–
+
+
–
–
+
+
Direction of nerve impulse
–
–
–
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
(b)
–
–
–
–
–
–
–
+
+
–
–
–
–
–
–
–
–
–
+
+
–
–
+
(c)
+
+
+
+
+
+
+
+
33
Animation: Action Potential
Propagation in Myelinated Neurons
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Animation: Action Potential
Propagation in Unmyelinated Neurons
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35
All-or-None Response
• If a neuron axon responds at all, it responds completely –
with an action potential (nerve impulse)
• A nerve impulse is conducted whenever a stimulus of
threshold intensity or above is applied to an axon
• All impulses carried on an axon are the same strength
36
Refractory Period
• Absolute Refractory Period
• Time when threshold stimulus does not start another
action potential
• Relative Refractory Period
• Time when stronger threshold stimulus can start another
action potential
37
Impulse Conduction
38
Animation: The Nerve Impulse
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39
10.3 Clinical Application
Factors Affecting Impulse Conduction
40
10.7: Synaptic Transmission
• This is where released neurotransmitters cross the
synaptic cleft and react with specific molecules called
receptors in the postsynaptic neuron membrane.
• Effects of neurotransmitters vary.
• Some neurotransmitters may open ion channels and
others may close ion channels.
41
Synaptic Potentials
• EPSP
• Excitatory postsynaptic potential
• Graded
• Depolarizes membrane of postsynaptic neuron
• Action potential of postsynaptic neuron becomes more likely
• IPSP
• Inhibitory postsynaptic potential
• Graded
• Hyperpolarizes membrane of postsynaptic neuron
• Action potential of postsynaptic neuron becomes less likely
42
Summation of
EPSPs and IPSPs
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• EPSPs and IPSPs are added
together in a process called
summation
• More EPSPs lead to greater
probability of an action
potential
Neuron
cell body
Nucleus
Presynaptic
knob
Presynaptic
axon
43
Neurotransmitters
44
Neurotransmitters
45
Neuropeptides
• Neurons in the brain or spinal cord synthesize neuropeptides.
• These neuropeptides act as neurotransmitters.
• Examples include:
• Enkephalins
• Beta endorphin
• Substance P
46
10.4 Clinical Application
Opiates in the Human Body
47
10.8: Impulse Processing
• Way the nervous system processes nerve impulses and acts
upon them
• Neuronal Pools
• Interneurons
• Work together to perform a common function
• May excite or inhibit
• Convergence
• Various sensory receptors
• Can allow for summation of impulses
• Divergence
• Branching axon
• Stimulation of many neurons ultimately
48
Neuronal Pools
• Groups of interneurons that make synaptic connections
with each other
• Interneurons work together to perform a common function
• Each pool receives input from other neurons
• Each pool generates output to other neurons
49
Convergence
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• Neuron receives input from several
neurons
• Incoming impulses represent
information from different types of
sensory receptors
1
2
• Allows nervous system to collect,
process, and respond to information
• Makes it possible for a neuron to
sum impulses from different sources
3
(a)
50
Divergence
• One neuron sends impulses
to several neurons
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Can amplify an impulse
4
• Impulse from a single neuron
in CNS may be amplified to
activate enough motor units
needed for muscle contraction
6
5
51
(b)
Important Points in Chapter 10:
Outcomes to be Assessed
10.1: Introduction
 Describe the general functions of the nervous system.
 Identify the two types of cells that comprise nervous tissue.
 Identify the two major groups of nervous system organs.
10.2: General Functions of the Nervous System
 List the functions of sensory receptors.
 Describe how the nervous system responds to stimuli.
10.3: Description of Cells of the Nervous System
 Describe the three major parts of a neuron.
 Define neurofibrils and chromatophilic substance.
52
Important Points in Chapter 10:
Outcomes to be Assessed
 Describe the relationship among myelin, the neurilemma, and the
nodes of Ranvier.
 Distinguish between the sources of white matter and gray matter.
10.4: Classification of Neurons and Neuroglia
 Identify structural and functional differences among neurons.
 Identify the types of neuroglia in the central nervous system and their
functions.
 Describe the Schwann cells of the peripheral nervous system.
10.5: The Synapse
 Define presynaptic and postsynaptic.
 Explain how information passes from a presynaptic to a postsynaptic 53
neuron.
Important Points in Chapter 10:
Outcomes to be Assessed
10.6: Cell Membrane Potential
 Explain how a cell membrane becomes polarized.
 Define resting potential, local potential, and action potential.
 Describe the events leading to the conduction of a nerve impulse.
 Compare nerve impulse conduction in myelinated and unmyelinated
neurons.
10.7: Synaptic Transmission
 Identify the changes in membrane potential associated with excitatory
and inhibitory neurotransmitters.
10.8: Impulse Processing
 Describe the basic ways in which the nervous system processes
information.
54
Quiz 10
Complete Quiz 10 now!
Read Chapter 11.
55