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prepared by
Meg Flemming
Austin Community College
CHAPTER
8
The Nervous
System
© 2013 Pearson Education, Inc.
Chapter 8 Learning Outcomes
•
•
•
•
•
8-1
• Describe the anatomical and functional divisions of the nervous
system.
8-2
• Distinguish between neurons and neuroglia on the basis of
structure and function.
8-3
• Describe the events involved in the generation and propagation of
an action potential.
8-4
• Describe the structure of a synapse, and explain the mechanism of
nerve impulse transmission at a synapse.
8-5
• Describe the three meningeal layers that surround the central
nervous system.
© 2013 Pearson Education, Inc.
Chapter 8 Learning Outcomes
•
•
•
•
•
8-6
• Discuss the roles of gray matter and white matter in the spinal cord.
8-7
• Name the major regions of the brain, and describe the locations
and functions of each.
8-8
• Name the cranial nerves, relate each pair of cranial nerves to its
principal functions, and relate the distribution pattern of spinal
nerves to the regions they innervate.
8-9
• Describe the steps in a reflex arc.
8-10
• Identify the principal sensory and motor pathways, and explain how
it is possible to distinguish among sensations that originate in
different areas of the body.
© 2013 Pearson Education, Inc.
Chapter 8 Learning Outcomes
•
•
•
8-11
• Describe the structures and functions of the sympathetic and
parasympathetic divisions of the autonomic nervous system.
8-12
• Summarize the effects of aging on the nervous system.
8-13
• Give examples of interactions between the nervous system and
other organ systems.
© 2013 Pearson Education, Inc.
The Nervous System and the Endocrine System
(Introduction)
• The nervous system and endocrine system
coordinate other organ systems to maintain
homeostasis
• The nervous system is fast, short acting
• The endocrine system is slower, but longer lasting
• The nervous system is the most complex system
in the body
© 2013 Pearson Education, Inc.
Functions of the Nervous System (8-1)
• Monitors the body's internal and external
environments
• Integrates sensory information
• Coordinates voluntary and involuntary responses
http://www.youtube.com/watch?v=kr7dGPOwzsA
© 2013 Pearson Education, Inc.
Divisions of the Nervous System (8-1)
• Anatomical divisions are:
• The central nervous system (CNS)
• Made up of the brain and spinal cord
• Integrates and coordinates input and output
• The peripheral nervous system (PNS)
• All the neural tissues outside of the CNS
• The connection between the CNS and the organs
© 2013 Pearson Education, Inc.
Divisions of the Nervous System (8-1)
• Functional divisions are:
• The afferent division
• Includes sensory receptors and neurons that send
information to the CNS
• The efferent division
• Includes neurons that send information to the effectors,
which are the muscles and glands
© 2013 Pearson Education, Inc.
Efferent Division of the Nervous System (8-1)
•
Further divided into:
•
The somatic nervous system (SNS)
•
•
Controls skeletal muscle
The autonomic nervous system (ANS)
•
Controls smooth and cardiac muscle, and glands
•
Has two parts
1. Sympathetic division
2. Parasympathetic division
© 2013 Pearson Education, Inc.
Figure 8-1 A Functional Overview of the Nervous System.
CENTRAL NERVOUS SYSTEM
Information
processing
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Motor commands
within
efferent division
includes
Somatic
nervous
system
Autonomic
nervous system
Parasympathetic Sympathetic
division
division
Receptors
Somatic sensory Visceral sensory
receptors (monitor receptors (monitor
internal conditions
the outside world
and the status
and our position
in it)
of other organ
systems)
© 2013 Pearson Education, Inc.
Effectors
Skeletal
muscle
Smooth
muscle
Cardiac
muscle
Glands
Checkpoint (8-1)
1.
Identify the two anatomical divisions of the
nervous system.
2.
Identify the two functional divisions of the
peripheral nervous system, and describe their
primary functions.
3.
What would be the effect of damage to the
afferent division of the PNS?
© 2013 Pearson Education, Inc.
Neurons (8-2)
• Cells that communicate with one another and other cells
•
Basic structure of a neuron includes:
• Cell body
• Dendrites
• Which receive signals
• Axons
• Which carry signals to the next cell
•
Axon terminals
• Bulb-shaped endings that form a synapse with the next cell
© 2013 Pearson Education, Inc.
Neurons (8-2)
• Have a very limited ability to regenerate when
damaged or destroyed
• Cell bodies contain:
• Mitochondria, free and fixed ribosomes, and rough
endoplasmic reticulum
• Free ribosomes and RER form Nissl bodies and give the
tissue a gray color (gray matter)
• The axon hillock
• Where electrical signal begins
© 2013 Pearson Education, Inc.
Figure 8-2 The Anatomy of a Representative Neuron.
Cell body
Mitochondrion
Golgi apparatus
Axon hillock
Dendrite
Axon terminals
Collateral
Nucleus
Axon (may be myelinated)
Nucleolus
Nerve cell body
Nucleolus
Nucleus
Axon hillock
Nissl bodies
Nissl bodies
Nerve cell body
LM x 1500
© 2013 Pearson Education, Inc.
Structural Classification of Neurons (8-2)
•
Based on the relationship of the dendrites to the cell body
• Multipolar neurons
• Are the most common in the CNS and have two or more dendrites and
one axon
• Unipolar neurons
• Have the cell body off to one side, most abundant in the afferent
division
• Bipolar neurons
• Have one dendrite and one axon with the cell body in the middle, and
are rare
© 2013 Pearson Education, Inc.
Figure 8-3 A Structural Classification of Neurons.
Multipolar neuron
Unipolar neuron
Bipolar neuron
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Sensory Neurons (8-2)
• Also called afferent neurons
• Total 10 million or more
• Receive information from sensory receptors
• Somatic sensory receptors
• Detect stimuli concerning the outside world, in the form of
external receptors
• And our position in it, in the form of proprioceptors
• Visceral or internal receptors
• Monitor the internal organs
© 2013 Pearson Education, Inc.
Motor Neurons (8-2)
• Also called efferent neurons
• Total about half a million in number
• Carry information to peripheral targets called
effectors
• Somatic motor neurons
• Innervate skeletal muscle
• Visceral motor neurons
• Innervate cardiac muscle, smooth muscle, and glands
© 2013 Pearson Education, Inc.
Interneurons (8-2)
• Also called association neurons
• By far the most numerous type at about 20 billion
• Are located in the CNS
• Function as links between sensory and motor
processes
• Have higher functions
• Such as memory, planning, and learning
© 2013 Pearson Education, Inc.
Neuroglial Cells (8-2)
•
Are supportive cells and make up about half of all neural
tissue
•
Four types are found in the CNS
1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal cells
•
Two types in the PNS
1. Satellite cells
2. Schwann cells
© 2013 Pearson Education, Inc.
Astrocytes (8-2)
• Large and numerous neuroglia in the CNS
• Maintain the blood–brain barrier
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Oligodendrocytes (8-2)
• Found in the CNS
• Produce an insulating membranous wrapping
around axons called myelin
• Small gaps between the wrappings called nodes of Ranvier
• Myelinated axons constitute the white matter of
the CNS
• Where cell bodies are gray matter
• Some axons are unmyelinated
© 2013 Pearson Education, Inc.
Microglia (8-2)
• The smallest and least numerous
• Phagocytic cells derived from white blood cells
• Perform essential protective functions such as
engulfing pathogens and cellular waste
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Ependymal Cells (8-2)
• Line the fluid-filled central canal of the spinal cord
and the ventricles of the brain
• The endothelial lining is called the ependyma
• It is involved in producing and circulating
cerebrospinal fluid around the CNS
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Figure 8-4 Neuroglia in the CNS.
Gray matter
White matter
CENTRAL
CANAL
Ependymal
cells
Gray
matter
Neurons
Myelinated
axons
Microglial
cell
Internode
White
matter
Myelin
(cut)
Axon
Node
Astrocyte
Oligodendrocyte
Capillary
© 2013 Pearson Education, Inc.
Basement
membrane
Neuroglial Cells in PNS (8-2)
• Satellite cells
• Surround and support neuron cell bodies
• Similar in function to the astrocytes in the CNS
• Schwann cells
• Cover every axon in PNS
• The surface is the neurilemma
• Produce myelin
© 2013 Pearson Education, Inc.
Figure 8-5 Schwann Cells and Peripheral Axons.
Nodes
Schwann cell nucleus
Myelin covering
internode
Neurilemma
Axons
Schwann
cell nucleus
Myelinated axon TEM x 14,048
A myelinated axon in the
PNS is covered by several
Schwann cells, each of
which forms a myelin sheath
around a portion of the axon.
This arrangement differs
from the way myelin forms in
the CNS; compare with
Figure 8-4.
© 2013 Pearson Education, Inc.
Unmyelinated TEM x 14,048
axon
A single Schwann cell can
encircle several unmyelinated axons. Every axon
in the PNS is completely
enclosed by Schwann
cells.
Organization of the Nervous System (8-2)
• In the PNS:
• Collections of nerve cell bodies are ganglia
• Bundled axons are nerves
• Including spinal nerves and cranial nerves
• Can have both sensory and motor components
© 2013 Pearson Education, Inc.
Organization of the Nervous System (8-2)
• In the CNS:
• Collections of neuron cell bodies are found in centers,
or nuclei
• Neural cortex is a thick layer of gray matter
• White matter in the CNS is formed by bundles of axons
called tracts, and in the spinal cord, form columns
• Pathways are either sensory or ascending tracts, or
motor or descending tracts
© 2013 Pearson Education, Inc.
Figure 8-6 The Anatomical Organization of the Nervous System.
CENTRAL NERVOUS SYSTEM
GRAY MATTER ORGANIZATION
PERIPHERAL
NERVOUS SYSTEM
GRAY MATTER
Ganglia
Collections of
neuron cell
bodies in the PNS
WHITE MATTER
Nerves
Bundles of axons
in the PNS
RECEPTORS
Neural Cortex
Gray matter on
the surface of
the brain
Nuclei
Collections of
Higher Centers
neuron cell
The most complex
bodies in the
centers in the
interior of the
brain
CNS
WHITE MATTER ORGANIZATION
Tracts
Columns
Bundles of CNS Several tracts
axons that share that form an
a common origin, anatomically
destination, and distinct mass
function
PATHWAYS
Centers and tracts that connect
the brain with other organs and
EFFECTORS systems in the body
Ascending (sensory) pathway
Descending (motor) pathway
© 2013 Pearson Education, Inc.
Centers
Collections of
neuron cell bodies
in the CNS; each
center has specific
processing
functions
Checkpoint (8-2)
4. Name the structural components of a typical neuron.
5. Examination of a tissue sample reveals unipolar neurons.
Are these more likely to be sensory neurons or motor
neurons?
6. Identify the neuroglia of the central nervous system.
7. Which type of glial cell would increase in number in the
brain tissue of a person with a CNS infection?
8. In the PNS, neuron cell bodies are located in ________
and surrounded by neuroglial cells called ________ cells.
© 2013 Pearson Education, Inc.
The Membrane Potential (8-3)
• A membrane potential exists because of:
• Excessive positive ionic charges on the outside of the
cell
• Excessive negative charges on the inside, creating a
polarized membrane
• An undisturbed cell has a resting membrane potential
measured in the inside of the cell in millivolts
• The resting membrane potential of neurons is –70 mV
© 2013 Pearson Education, Inc.
Factors Determining Membrane Potential (8-3)
• Extracellular fluid (ECF) is high in Na+ and CI–
• Intracellular fluid (ICF) is high in K+ and negatively charged
proteins (Pr –)
• Proteins are non-permeating, staying in the ICF
• Some ion channels are always open
• Called leak channels
• Some are open or closed
• Called gated channels
© 2013 Pearson Education, Inc.
Factors Determining Membrane Potential (8-3)
• Na+ can leak in
• But the membrane is more permeable to K+
• Allowing K+ to leak out faster
• Na+/K+ exchange pump exchanges 3 Na+ for every
2 K+
• Moving Na+ out as fast as it leaks in
• Cell experiences a net loss of positive ions
• Resulting in a resting membrane charge of –70 mV
© 2013 Pearson Education, Inc.
Figure 8-7 The Resting Potential Is the Membrane Potential of an Undisturbed Cell.
EXTRACELLULAR FLUID
–70
–30
0
+30
mV
Na+ leak
channel
K+ leak
channel
Sodium–
potassium
exchange
pump
Plasma
membrane
CYTOSOL
Protein
KEY
Sodium ion (Na+)
Protein
Protein
Potassium ion (K+)
Chloride ion (Cl–)
© 2013 Pearson Education, Inc.
Changes in Membrane Potential (8-3)
• Stimuli alter membrane permeability to Na+ or K+
• Or alter activity of the exchange pump
• Types include:
• Cellular exposure to chemicals
• Mechanical pressure
• Temperature changes
• Changes in the ECF ion concentration
• Result is opening of a gated channel
• Increasing the movement of ions across the membrane
© 2013 Pearson Education, Inc.
Changes in Membrane Potential (8-3)
• Opening of Na+ channels results in an influx of Na+
• Moving the membrane toward 0 mV, a shift called
depolarization
• Opening of K+ channels results in an efflux of K+
• Moving the membrane further away from 0 mV, a shift
called hyperpolarization
• Return to resting from depolarization: repolarizing
© 2013 Pearson Education, Inc.
Graded Potentials (8-3)
• Local changes in the membrane that fade over
distance
• All cells experience graded potentials when
stimulated
• And can result in the activation of smaller cells
• Graded potentials by themselves cannot trigger
activation of large neurons and muscle fibers
• Referred to as having excitable membranes
© 2013 Pearson Education, Inc.
Action Potentials (8-3)
• A change in the membrane that travels the entire
length of neurons
• A nerve impulse
• If a combination of graded potentials causes the
membrane to reach a critical point of
depolarization, it is called the threshold
• Then an action potential will occur
© 2013 Pearson Education, Inc.
Action Potentials (8-3)
• Are all-or-none and will propagate down the
length of the neuron
• From the time the voltage-gated channels open
until repolarization is finished:
• The membrane cannot respond to further stimulation
• This period of time is the refractory period
• And limits the rate of response by neurons
© 2013 Pearson Education, Inc.
Figure 8-8 The Generation of an Action Potential
FIGURE 8-8
SPOTLIGHT
The Generation of an Action Potential
Sodium channels close,
voltage-gated potassium channels
open, and potassium ions move out
of the cell. Repolarization begins.
3
+30
Axon hillock
First part of axon to
reach threshold
Membrane potential (mV)
DEPOLARIZATION
0
Potassium channels
close, and both sodium
and potassium
channels return to their
Voltage-gated sodium
normal states.
channels open and
sodium ions move
into the cell. The
4
membrane potential
rises to +30 mV.
2
Resting
potential
–40
Threshold
–60
–70
1
A graded
depolarization
brings an area of
excitable membrane
to threshold (–60
mV).
REFRACTORY PERIOD
During the refractory period,
the membrane cannot respond
to further stimulation.
0
1
Resting
Potential
–70 mV
Depolarization to
Threshold
–60 mV
2
Activation of Sodium
Channels and Rapid
Depolarization
3
REPOLARIZATION
Inactivation of Sodium
Channels and
Activation
of Potassium Channels
Time (msec)
4
1
Closing of Potassium
Channels
–90 mV
+10 mV
2
Resting
Potential
–70 mV
+30 mV
Local
current
The axon membrane
contains both
voltage-gated sodium
channels and
voltage-gated
potassium channels
that are closed when
the membrane is at the
resting potential.
= Sodium ion
= Potassium ion
© 2013 Pearson Education, Inc.
The stimulus that
begins an action
potential is a graded
depolarization large
enough to open
voltage-gated sodium
channels. The opening
of the channels occurs
at a membrane potential
known as the threshold.
When the voltage-gated
sodium channels open,
sodium ions rush into the
cytoplasm, and rapid
depolarization occurs.
The inner membrane
surface now contains
more positive ions than
negative ones, and the
membrane potential has
changed from –60 mV
to a positive value.
As the membrane
potential approaches
+30 mV, voltage-gated
sodium channels close.
This step coincides with
the opening of voltagegated potassium
channels. Positively
charged potassium ions
move out of the cytosol,
shifting the membrane
potential back toward
resting levels. Repolarization now begins.
The voltage-gated sodium
channels remain
inactivated until the
membrane has repolarized to near threshold
levels. The voltage-gated
potassium channels
begin closing as the
membrane reaches the
normal resting potential
(about –70 mV). Until all
have closed, potassium
ions continue to leave the
cell. This produces a brief
hyperpolarization.
As the voltage-gated
potassium channels
close, the
membrane potential
returns to normal
resting levels. The
action potential is
now over, and the
membrane is once
again at the resting
potential.
Figure 8-8 The Generation of an Action Potential
Sodium channels close, voltagegated potassium channels open,
and potassium ions move out of the
cell. Repolarization begins.
3
+30
D E P O L A R I Z AT I O N
R E P O L A R I Z AT I O N
0
2
Resting
potential
–40
–60
–70
Potassium channels
close, and both sodium
and potassium channels return to their
normal states.
Voltage-gated sodium
channels open and
sodium ions move into
the cell. The membrane
potential rises to +30
mV.
Threshold
1
A graded
depolarization brings
an area of excitable
membrane to threshold (–60 mV).
4
REFRACTORY PERIOD
During the refractory period,
the membrane cannot
respond to further stimulation.
0
© 2013 Pearson Education, Inc.
Time (msec)
1
2
Figure 8-8 The Generation of an Action Potential
Resting Potential
–70 mV
Depolarization to
Threshold
–60 mV
The axon membrane
contains both
voltage-gated sodium
channels and
voltage-gated
potassium channels
that are closed when
the membrane is at the
resting potential.
= Sodium ion
= Potassium ion
© 2013 Pearson Education, Inc.
Activation of Sodium
Channels and Rapid
Depolarization
+10 mV
Local
current
The stimulus that
begins an action
potential is a graded
depolarization large
enough to open
voltage-gated sodium
channels. The opening
of the channels occurs
at a membrane potential
known as the threshold.
When the voltage-gated
sodium channels open,
sodium ions rush into the
cytoplasm, and rapid
depolarization occurs.
The inner membrane
surface now contains
more positive ions than
negative ones, and the
membrane potential has
changed from
–60 mV to a positive
value.
Figure 8-8 The Generation of an Action Potential
Inactivation of Sodium
Channels and
Activation of Potassium
Channels
Closing of Potassium Channels
–90 mV
Resting
Potential
–70 mV
+30 mV
As the membrane
potential approaches
+30 mV, voltage-gated
sodium channels close.
This step coincides with
the opening of voltagegated potassium
channels. Positively
charged potassium ions
move out of the cytosol,
shifting the membrane
potential back toward
resting levels. Repolarization now begins.
© 2013 Pearson Education, Inc.
The voltage-gated sodium
channels remain
inactivated until the
membrane has repolarized to near threshold
levels. The voltage-gated
potassium channels
begin closing as the
membrane reaches the
normal resting potential
(about –70 mV). Until all
have closed, potassium
ions continue to leave the
cell. This produces a brief
hyperpolarization.
As the voltage-gated
potassium channels
close, the membrane potential returns to normal resting levels. The
action potential is
now over, and the
membrane is once
again at the resting
potential.
Propagation of an Action Potential (8-3)
• Occurs when local changes in the membrane in
one site:
• Result in the activation of voltage-gated channels in the next
adjacent site of the membrane
• This causes a wave of membrane potential
changes
• Continuous propagation
• Occurs in unmyelinated fibers and is relatively slow
• Saltatory propagation
• Is in myelinated axons and is faster
© 2013 Pearson Education, Inc.
Figure 8-9 The Propagation of Action Potentials over Unmyelinated and Myelinated Axons.
Action potential propagation along an
unmyelinated axon
Stimulus
depolarizes
membrane to
threshold
EXTRACELLULAR FLUID
Action potential propagation along a
myelinated axon
Stimulus
depolarizes
membrane to
threshold
EXTRACELLULAR FLUID
Myelinated
Internode
Plasma membrane CYTOSOL
Myelinated
Internode
Plasma membrane
Myelinated
Internode
Myelinated
Internode
CYTOSOL
Myelinated
Internode
Myelinated
Internode
Myelinated
Internode
Myelinated
Internode
Local current
Myelinated
Internode
Local current
Repolarization
(refractory period)
© 2013 Pearson Education, Inc.
Repolarization
(refractory period)
Checkpoint (8-3)
9. What effect would a chemical that blocks the voltage-gated
sodium channels in a neuron's plasma membrane have on the
neuron's ability to depolarize?
10. What effect would decreasing the concentration of extracellular
potassium have on the membrane potential of a neuron?
11. List the steps involved in the generation and propagation of an
action potential.
12. Two axons are tested for propagation velocities. One carries
action potentials at 50 meters per second, the other at 1 meter
per second. Which axon is myelinated?
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The Synapse (8-4)
• A junction between a neuron and another cell
• Occurs because of chemical messengers called
neurotransmitters
• Communication happens in one direction only
• Between a neuron and another cell type is a neuroeffector
junction
• Such as the neuromuscular junction or neuroglandular junction
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A Synapse between Two Neurons (8-4)
• Occurs:
• Between the axon terminals of the presynaptic neuron
• Across the synaptic cleft
• To the dendrite or cell body of the postsynaptic neuron
• Neurotransmitters
• Stored in vesicles of the axon terminals
• Released into the cleft and bind to receptors on the
postsynaptic membrane
PLAY
ANIMATION Neurophysiology: Synapse
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Figure 8-10 The Structure of a Typical Synapse.
Axon of
presynaptic cell
Axon
terminal
Mitochondrion
Synaptic
vesicles
Presynaptic
membrane
Postsynaptic Synaptic
membrane
cleft
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The Neurotransmitter ACh (8-4)
•
Activates cholinergic synapses in four steps
1. Action potential arrives at the axon terminal
2. ACh is released and diffuses across synaptic cleft
3. ACh binds to receptors and triggers depolarization of
the postsynaptic membrane
4. ACh is removed by AChE (acetylcholinesterase)
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Figure 8-11 The Events at a Cholinergic Synapse.
An action potential arrives and
depolarizes the axon terminal
Presynaptic
neuron
Synaptic
vesicles
Action potential
EXTRACELLULAR
FLUID
Axon
terminal
AChE
POSTSYNAPTIC
NEURON
Extracellular Ca2+ enters the axon
terminal, triggering the exocytosis of ACh
ACh
Ca2+
Ca2+
Synaptic cleft
Chemically regulated
sodium ion channels
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Figure 8-11 The Events at a Cholinergic Synapse.
ACh binds to receptors and depolarizes
the postsynaptic membrane
Initiation of
action potential
if threshold is
reached
ACh is removed by AChE
Propagation of
action potential
(if generated)
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Table 8-1 The Sequence of Events at a Typical Cholinergic Synapse
© 2013 Pearson Education, Inc.
Other Important Neurotransmitters (8-4)
• Norepinephrine (NE)
• In the brain and part of the ANS, is found in adrenergic
synapses
• Dopamine, GABA, and serotonin
• Are CNS neurotransmitters
• At least 50 less-understood neurotransmitters
• NO and CO
• Are gases that act as neurotransmitters
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Excitatory vs. Inhibitory Synapses (8-4)
• Usually, ACh and NE trigger depolarization
• An excitatory response
• With the potential of reaching threshold
• Usually, dopamine, GABA, and serotonin trigger
hyperpolarization
• An inhibitory response
• Making it farther from threshold
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Neuronal Pools (8-4)
• Multiple presynaptic neurons can synapse with
one postsynaptic neuron
• If they all release excitatory neurotransmitters:
• Then an action potential can be triggered
• If they all release an inhibitory neurotransmitter:
• Then no action potential can occur
• If half release excitatory and half inhibitory neurotransmitters:
• They cancel, resulting in no action
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Neuronal Pools (8-4)
• A term that describes the complex grouping of
neural pathways or circuits
• Divergence
• Is a pathway that spreads information from one neuron
to multiple neurons
• Convergence
• Is when several neurons synapse with a single
postsynaptic neuron
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Figure 8-12 Two Common Types of Neuronal Pools.
Divergence
A mechanism for
spreading stimulation to
multiple neurons or
neuronal pools in the
CNS
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Convergence
A mechanism for providing
input to a single neuron from
multiple sources
Checkpoint (8-4)
13. Describe the general structure of a synapse.
14. What effect would blocking calcium channels at
a cholinergic synapse have on synapse
function?
15. What type of neural circuit permits both
conscious and subconscious control of the same
motor neurons?
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The Meninges (8-5)
•
The neural tissue in the CNS is protected by
three layers of specialized membranes
1. Dura mater
2. Arachnoid
3. Pia mater
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The Dura Mater (8-5)
• Is the outer, very tough covering
• The dura mater has two layers, with the outer layer
fused to the periosteum of the skull
• Dural folds contain large veins, the dural sinuses
• In the spinal cord the dura mater is separated from the
bone by the epidural space
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The Arachnoid
• Is separated from the dura mater by the subdural
space
• That contains a little lymphatic fluid
• Below the epithelial layer is arachnoid space
• Created by a web of collagen fibers
• Contains cerebrospinal fluid
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The Pia Mater
• Is the innermost layer
• Firmly bound to the neural tissue underneath
• Highly vascularized
• Providing needed oxygen and nutrients
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Checkpoint (8-5)
16. Identify the three meninges surrounding the
CNS.
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Spinal Cord Structure (8-6)
• The major neural pathway between the brain and
the PNS
• Can also act as an integrator in the spinal reflexes
• Involving the 31 pairs of spinal nerves
• Consistent in diameter except for the cervical
enlargement and lumbar enlargement
• Where numerous nerves supply upper and lower limbs
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Spinal Cord Structure (8-6)
• Central canal
• A narrow passage containing cerebrospinal fluid
• Surface of the spinal cord is indented by the:
• Posterior median sulcus
• Deeper anterior median fissure
© 2013 Pearson Education, Inc.
31 Spinal Segments (8-6)
• Identified by a letter and number relating to the
nearby vertebrae
• Each has a pair of dorsal root ganglia
• Containing the cell bodies of sensory neurons with
axons in dorsal root
• Ventral roots contain motor neuron axons
• Roots are contained in one spinal nerve
© 2013 Pearson Education, Inc.
Figure 8-14a Gross Anatomy of the Spinal Cord.
Cervical spinal
nerves
Thoracic
spinal
nerves
C1
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
Posterior
median sulcus
T10
T11
T12
L1
L2
Lumbar
spinal
nerves
Cervical
enlargement
Lumbar
enlargement
Inferior tip of
spinal cord
L3
L4
Cauda equina
L5
Sacral spinal
nerves
S
S11
S
S22
S
S33
S
S44
S
S55
Coccygeal
nerve (Co1)
© 2013 Pearson Education, Inc.
In this superficial view of the
adult spinal cord, the
designations to the left identify
the spiral nerves.
Figure 8-14b Gross Anatomy of the Spinal Cord.
Posterior median sulcus
Dorsal root
Dorsal root
ganglion
Gray
matter
Central
canal
White matter
Spinal Ventral
nerve root
© 2013 Pearson Education, Inc.
Anterior median fissure
C3
This cross section through the
cervical region of the spinal cord
shows some prominent features
and
the arrangement of gray matter and
Sectional Anatomy of the Spinal Cord (8-6)
• The central gray matter is made up of glial cells
and nerve cell bodies
• Projections of gray matter are called horns
• Which extend out into the white matter
• White matter is myelinated and unmyelinated
axons
• The location of cell bodies in specific nuclei of the
gray matter relate to their function
© 2013 Pearson Education, Inc.
Sectional Anatomy of the Spinal Cord (8-6)
• Posterior gray horns are somatic and visceral
sensory nuclei
• Lateral gray horns are visceral (ANS) motor nuclei
• The anterior gray horns are somatic motor nuclei
• White matter can be organized into three columns
• Which contain either ascending tracts to the brain, or
descending tracts from the brain to the PNS
© 2013 Pearson Education, Inc.
Figure 8-15 Sectional Anatomy of the Spinal Cord.
Posterior white column
Dorsal
root
ganglion
Posterior
gray horn
Lateral
Lateral
white gray horn
column
Anterior
gray
horn
Posterior
median sulcus
Posterior gray
commissure
Functional Organization
of Gray Matter
The cell bodies of neurons in the
gray matter of the spinal cord are
organized into functional groups
called nuclei.
Somatic
Visceral
Visceral
Somatic
Sensory nuclei
Motor nuclei
Ventral root
Anterior gray commissure
Anterior white commissure
Anterior white column
Anterior median fissure
The left half of this sectional view shows important anatomical landmarks, including the
three columns of white matter. The right half indicates the functional organization of the
nuclei in the anterior, lateral, and posterior gray horns.
POSTERIOR
Structural Organization
of Gray Matter
The projections of gray matter
toward the outer surface of the
spinal cord are called horns.
Posterior gray horn
Posterior
median sulcus
Posterior gray
commissure
Dura mater
Arachnoid mater
(broken)
Central canal
Anterior gray
commissure
Anterior median
fissure
Pia mater
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Lateral gray horn
Dorsal
root
ANTERIOR
Anterior gray horn
Dorsal root
ganglion
Ventral root
A micrograph of a section through the spinal cord, showing
major landmarks in and surrounding the cord.
Figure 8-15a Sectional Anatomy of the Spinal Cord.
Posterior white column
Dorsal root
ganglion
Lateral
white
column
Posterior
gray horn
Lateral
gray horn
Anterior
gray
horn
Posterior
median sulcus
Posterior gray
commissure
Somatic
Visceral
Visceral
Somatic
Functional Organization
of Gray Matter
The cell bodies of neurons in the
gray matter of the spinal cord are
organized into functional groups
called nuclei.
Sensory nuclei
Motor nuclei
Ventral root
Anterior white column
Anterior gray commissure
Anterior white commissure
Anterior median fissure
The left half of this sectional view shows important anatomical landmarks, including the
three columns of white matter. The right half indicates the functional organization of the
nuclei in the anterior, lateral, and posterior gray horns.
© 2013 Pearson Education, Inc.
Figure 8-15b Sectional Anatomy of the Spinal Cord.
POSTERIOR
Posterior
median sulcus
Posterior gray
commissure
Dura mater
Arachnoid mater
(broken)
Central canal
Anterior gray
commissure
Anterior median
fissure
Pia mater
Structural Organization
of Gray Matter
The projections of gray matter
toward the outer surface of the
spinal cord are called horns.
Posterior gray horn
Lateral gray horn
Dorsal
root
ANTERIOR
Anterior gray horn
Dorsal root
ganglion
Ventral root
A micrograph of a section through the spinal cord, showing
major landmarks in and surrounding the cord.
© 2013 Pearson Education, Inc.
Checkpoint (8-6)
17. Damage to which root of a spinal nerve would
interfere with motor function?
18. A person with polio has lost the use of his leg
muscles. In which areas of his spinal cord could
you locate virus-infected neurons?
19. Why are spinal nerves also called mixed
nerves?
© 2013 Pearson Education, Inc.
Six Major Regions of the Brain (8-7)
1. The cerebrum
2. The diencephalon
3. The midbrain
4. The pons
5. The medulla oblongata
6. The cerebellum
© 2013 Pearson Education, Inc.
Major Structures of the Brain (8-7)
• The cerebrum
• Is divided into paired cerebral hemispheres
• Deep to the cerebrum is the diencephalon
• Which is divided into the thalamus, the hypothalamus,
and the epithalamus
• The brain stem
• Contains the midbrain, pons, and medulla oblongata
• The cerebellum
• Is the most inferior/posterior part
© 2013 Pearson Education, Inc.
Figure 8-16a The Brain.
Right cerebral hemisphere
CEREBRUM
Left cerebral hemisphere
Longitudinal fissure
A
N
T
E
R
I
O
R
Cerebral veins and arteries
below arachnoid mater
© 2013 Pearson Education, Inc.
CEREBELLUM
Superior view
P
O
S
T
E
R
I
O
R
Figure 8-16b The Brain.
Central sulcus
Precentral gyrus
Postcentral
gyrus
Parietal
lobe
Frontal lobe of left
cerebral hemisphere
Lateral sulcus
Occipital
lobe
Temporal lobe
CEREBELLUM
PONS
Lateral view
© 2013 Pearson Education, Inc.
MEDULLA OBLONGATA
Figure 8-16c The Brain.
Corpus Precentral Central
sulcus
callosum gyrus
Postcentral
gyrus
Fornix
Frontal lobe
Thalamus
Hypothalamus
DIENCEPHALON
Pineal gland
(part of epithalamus)
Parieto-occipital sulcus
Optic
chiasm
Mamillary body
Temporal lobe
MIDBRAIN
Brain stem PONS
MEDULLA OBLONGATA
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CEREBELLUM
Sagittal section
The Ventricles of the Brain (8-7)
• Filled with cerebrospinal fluid and lined with
ependymal cells
• The two lateral ventricles within each cerebral
hemisphere drain through the:
• Interventricular foramen into the:
• Third ventricle in the diencephalon, which drains
through the cerebral aqueduct into the:
• Fourth ventricle, which drains into the central canal
© 2013 Pearson Education, Inc.
Figure 8-17 The Ventricles of the Brain.
Cerebral hemispheres
Ventricles of
the Brain
Cerebral
hemispheres
Lateral
ventricles
Interventricular
foramen
Third
ventricle
Cerebral
aqueduct
Pons
Medulla oblongata
Spinal cord
Fourth
ventricle
Central canal
A lateral view of the ventricles
© 2013 Pearson Education, Inc.
Central canal
Cerebellum
An anterior view of the ventricles
Cerebrospinal Fluid (8-7)
• CSF
• Surrounds and bathes the exposed surfaces of the CNS
• Floats the brain
• Transports nutrients, chemicals, and wastes
• Is produced by the choroid plexus
• Continually secreted and replaced three times per day
• Circulation from the fourth ventricle into the
subarachnoid space into the dural sinuses
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Figure 8-18a The Formation and Circulation of Cerebrospinal Fluid.
Extension of choroid
plexus into
lateral ventricle
Choroid plexus
of third ventricle
Cerebral
aqueduct
Lateral aperture
Choroid plexus of
fourth ventricle
Median aperture
Arachnoid mater
Subarachnoid space
Dura mater
© 2013 Pearson Education, Inc.
A sagittal section of the CNS.
Cerebrospinal fluid, formed in
the choroid plexus, circulates
along the routes indicated by
the red arrows.
Arachnoid
granulations
Superior
sagittal
sinus
Central canal
Spinal cord
Figure 8-18b The Formation and Circulation of Cerebrospinal Fluid.
Superior
sagittal sinus
Cranium
Dura mater
(outer layer)
Arachnoid
granulation
Fluid
movement
Dura mater
(inner layer)
Cerebral
cortex
The relationship of the
arachnoid
granulations
and dura
mater.
© 2013 Pearson Education, Inc.
Subdural
space
Arachnoid
mater
Pia
mater
Subarachnoid
space
The Cerebrum (8-7)
• Contains an outer gray matter called the cerebral
cortex
• Deep gray matter in the cerebral nuclei and white matter of
myelinated axons beneath the cortex and around the nuclei
• The surface of the cerebrum
• Folds into gyri
• Separated by depressions called sulci or deeper grooves
called fissures
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The Cerebral Hemispheres (8-7)
• Are separated by the longitudinal fissure
• The central sulcus
• Extends laterally from the longitudinal fissure
• The frontal lobe
• Is anterior to the central sulcus
• Is bordered inferiorly by the lateral sulcus
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The Cerebral Hemispheres (8-7)
• The temporal lobe
• Inferior to the lateral sulcus
• Overlaps the insula
• The parietal lobe
• Extends between the central sulcus and the parietooccipital sulcus
© 2013 Pearson Education, Inc.
The Cerebral Hemispheres (8-7)
• The occipital lobe
• Located most posteriorly
• The lobes are named for the cranial bone above it
• Each lobe has sensory regions and motor regions
• Each hemisphere sends and receives information
from the opposite side of the body
© 2013 Pearson Education, Inc.
Motor and Sensory Areas of the Cortex (8-7)
• Are divided by the central sulcus
• The precentral gyrus of the frontal lobe
• Contains the primary motor cortex
• The postcentral gyrus of the parietal lobe
• Contains the primary sensory cortex
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Motor and Sensory Areas of Cortex (8-7)
• The visual cortex is in the occipital lobe
• The gustatory, auditory, and olfactory cortexes
are in the temporal lobe
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Association Areas (8-7)
• Interpret incoming information
• Coordinate a motor response, integrating the
sensory and motor cortexes
• The somatic sensory association area
• Helps to recognize touch
• The somatic motor association area
• Is responsible for coordinating movement
© 2013 Pearson Education, Inc.
Figure 8-19 The Surface of the Cerebral Hemispheres.
Primary motor cortex
(precentral gyrus)
Central sulcus
Primary sensory cortex
(postcentral gyrus)
Somatic motor association
area (premotor cortex)
PARIETAL LOBE
Somatic sensory
association area
FRONTAL LOBE
Visual association
area
OCCIPITAL LOBE
Visual cortex
Auditory
association area
Prefrontal cortex
Gustatory cortex
Insula
Lateral sulcus
Auditory cortex
Olfactory cortex
TEMPORAL LOBE
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Cortical Connections (8-7)
• Regions of the cortex are linked by the deeper
white matter
• The left and right hemispheres are linked across
the corpus callosum
• Other axons link the cortex with:
• The diencephalon, brain stem, cerebellum, and spinal
cord
© 2013 Pearson Education, Inc.
Higher-Order Centers (8-7)
• Integrative areas, usually only in the left
hemisphere
• The general interpretive area or Wernicke's area
• Integrates sensory information to form visual and auditory
memory
• The speech center or Broca's area
• Regulates breathing and vocalization, the motor skills
needed for speaking
© 2013 Pearson Education, Inc.
The Prefrontal Cortex (8-7)
• In the frontal lobe
• Coordinates information from the entire cortex
• Skills such as:
• Predicting time lines
• Making judgments
• Feelings such as:
• Frustration, tension, and anxiety
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Hemispheric Lateralization (8-7)
• The concept that different brain functions can and
do occur on one side of the brain
• The left hemisphere tends to be involved in language
skills, analytical tasks, and logic
• The right hemisphere tends to be involved in analyzing
sensory input and relating it to the body, as well as
analyzing emotional content
© 2013 Pearson Education, Inc.
Figure 8-20 Hemispheric Lateralization.
RIGHT HAND
LEFT HAND
Prefrontal
cortex
Prefrontal
cortex
Speech center
Anterior commissure
C
O
R
P
U
S
C
A
L
L
O
S
U
M
Writing
Auditory cortex
(right ear)
General interpretive
center (language and
mathematical calculation)
Analysis by touch
Auditory cortex
(left ear)
Spatial visualization
and analysis
Visual cortex
(right visual field)
Visual cortex
(left visual field)
LEFT
HEMISPHERE
© 2013 Pearson Education, Inc.
RIGHT
HEMISPHERE
The Electroencephalogram (8-7)
• EEG
• A printed record of brain wave activity
• Can be interpreted to diagnose brain disorders
• More modern techniques
• Brain imaging, using the PET scan and MRIs, has
allowed extensive "mapping" of the brain's functional
areas
© 2013 Pearson Education, Inc.
Figure 8-21 Brain Waves.
Patient being wired
for EEG monitoring
Alpha waves are
characteristic of
normal resting adults
Beta waves typically
accompany intense
concentration
Theta waves are
seen in children and
in frustrated adults
Delta waves occur
in deep sleep and in
certain pathological
conditions
0 Seconds 1
© 2013 Pearson Education, Inc.
2
3
4
Memory (8-7)
•
Fact memory
• The recall of bits of information
•
Skill memory
• Learned motor skill that can become incorporated into unconscious
memory
•
Short-term memory
• Doesn't last long unless rehearsed
• Converting into long-term memory through memory consolidation
•
Long-term memory
• Remains for long periods, sometimes an entire lifetime
•
Amnesia
• Memory loss as a result of disease or trauma
© 2013 Pearson Education, Inc.
The Basal Nuclei (8-7)
• Masses of gray matter
• Caudate nucleus
• Lies anterior to the lentiform nucleus
• Which contains the medial globus pallidus and the lateral
putamen
• Inferior to the caudate and lentiform nuclei is the amygdaloid body
or amygdala
• Basal nuclei
• Subconscious control of skeletal muscle tone
© 2013 Pearson Education, Inc.
Figure 8-22 The Basal Nuclei.
Head of caudate
nucleus
Lentiform nucleus
Thalamus
Tail of caudate
nucleus
Amygdaloid
body
Head of
caudate
nucleus
Lateral view of a transparent brain,
showing the relative positions of
the basal nuclei
Corpus
callosum
Lateral
ventricle
Insula
Amygdaloid
Lentiform Putamen
nucleus Globus pallidus
body
Frontal section
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Tip of
lateral
ventricle
The Limbic System (8-7)
• Includes the olfactory cortex, basal nuclei, gyri, and
tracts between the cerebrum and diencephalon
• A functional grouping, rather than an anatomical one
• Establishes the emotional states
• Links the conscious with the unconscious
• Aids in long-term memory with help of the
hippocampus
© 2013 Pearson Education, Inc.
Figure 8-23 The Limbic System.
Cingulate gyrus
Corpus callosum
Thalamic nuclei
Hypothalamic
nuclei
Olfactory tract
Amygdaloid body
Hippocampus
© 2013 Pearson Education, Inc.
Fornix
Mamillary body
The Diencephalon (8-7)
•
Contains switching and relay centers
•
Centers integrate conscious and unconscious sensory
information and motor commands
•
Surround third ventricle
•
Three components
1. Epithalamus
2. Thalamus
3. Hypothalamus
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The Epithalamus (8-7)
• Lies superior to the third ventricle and forms the
roof of the diencephalon
• The anterior part contains choroid plexus
• The posterior part contains the pineal gland that
is endocrine and secretes melatonin
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The Thalamus (8-7)
• The left and right thalamus are separated by the
third ventricle
• The final relay point for sensory information
• Only a small part of this input is sent on to the
primary sensory cortex
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The Hypothalamus (8-7)
• Lies inferior to the third ventricle
• The subconscious control of skeletal muscle
contractions is associated with strong emotion
• Adjusts the pons and medulla functions
• Coordinates the nervous and endocrine systems
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The Hypothalamus (8-7)
• Secretes hormones
• Produces sensations of thirst and hunger
• Coordinates voluntary and ANS function
• Regulates body temperature
• Coordinates daily cycles
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The Midbrain (8-7)
• Contains various nuclei
• Two pairs involved in visual and auditory processing, the colliculi
• Contains motor nuclei for cranial nerves III and IV
• Cerebral peduncles contain descending fibers
• Reticular formation is a network of nuclei related to the
state of wakefulness
• The substantia nigra influence muscle tone
© 2013 Pearson Education, Inc.
The Pons (8-7)
• Links the cerebellum with the midbrain,
diencephalon, cerebrum, and spinal cord
• Contains sensory and motor nuclei for cranial
nerves V, VI, VII, and VIII
• Other nuclei influence rate and depth of respiration
© 2013 Pearson Education, Inc.
The Cerebellum (8-7)
• An automatic processing center
• Which adjusts postural muscles to maintain balance
• Programs and fine-tunes movements
• The cerebellar peduncles
• Are tracts that link the cerebral cortex, basal nuclei, and brain stem
• Ataxia
• Is disturbance of coordination
• Can be caused by damage to the cerebellum
© 2013 Pearson Education, Inc.
The Medulla Oblongata (8-7)
• Connects the brain with the spinal cord
• Contains sensory and motor nuclei for cranial nerves VIII,
IX, X, XI, and XII
• Contains reflex centers
• Cardiovascular centers
• Adjust heart rate and arteriolar diameter
• Respiratory rhythmicity centers
• Regulate respiratory rate
© 2013 Pearson Education, Inc.
Figure 8-24a The Diencephalon and Brain Stem.
Cerebral
peduncle
Optic tract
Cranial
nerves
N II
N III
N IV
Thalamus
Diencephalon
Thalamic nuclei
Midbrain
Superior colliculus
Inferior colliculus
NV
N VI Pons
N VII
N VIII
N IX
NX
N XI
N XII
Spinal
nerve C1
Spinal
nerve C2
© 2013 Pearson Education, Inc.
Cerebellar peduncles
Medulla
oblongata
Spinal
cord
Lateral view
Figure 8-24b The Diencephalon and Brain Stem.
N IV
Choroid plexus
Thalamus
Third ventricle
Pineal gland
Corpora quadrigemina
Superior colliculi
Inferior colliculi
Cerebral peduncle
Cerebellar peduncles
Choroid plexus in roof
of fourth ventricle
Dorsal roots
of spinal nerves
C1 and C2
Posterior view
© 2013 Pearson Education, Inc.
Checkpoint (8-7)
20. Describe one major function of each of the six regions of
the brain.
21. The pituitary gland links the nervous and endocrine
systems. To which portion of the diencephalon is it
attached?
22. How would decreased diffusion across the arachnoid
granulations affect the volume of cerebrospinal fluid in the
ventricles?
23. Mary suffers a head injury that damages her primary
motor cortex. Where is this area located?
© 2013 Pearson Education, Inc.
Checkpoint (8-7)
24. What senses would be affected by damage to the
temporal lobes of the cerebrum?
25. The thalamus acts as a relay point for all but what type of
sensory information?
26. Changes in body temperature stimulate which area of the
diencephalon?
27. The medulla oblongata is one of the smallest sections of
the brain. Why can damage to it cause death, whereas
similar damage in the cerebrum might go unnoticed?
© 2013 Pearson Education, Inc.
Peripheral Nervous System (8-8)
• Links the CNS to the rest of the body through
peripheral nerves
• They include the cranial nerves and the spinal
nerves
• The cell bodies of sensory and motor neurons are
contained in the ganglia
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
• 12 pairs, noted as Roman numerals I through XII
• Some are:
• Only motor pathways
• Only sensory pathways
• Mixed having both sensory and motor neurons
• Often remembered with a mnemonic
• "Oh, Once One Takes The Anatomy Final, Very Good
Vacations Are Heavenly"
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
• The olfactory nerves (N I)
• Are connected to the cerebrum
• Carry information concerning the sense of smell
• The optic nerves (N II)
• Carry visual information from the eyes, through the
optic foramina of the orbits to the optic chiasm
• Continue as the optic tracts to the nuclei of the thalamus
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
• The oculomotor nerves (N III)
• Motor only, arising in the midbrain
• Innervate four of six extrinsic eye muscles and the
intrinsic eye muscles that control the size of the pupil
• The trochlear nerves (N IV)
• Smallest, also arise in the midbrain
• Innervate the superior oblique extrinsic muscles of the
eyes
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
•
The trigeminal nerves (N V)
•
Have nuclei in the pons, are the largest cranial nerves
•
Have three branches
1. The ophthalmic
•
From the orbit, sinuses, nasal cavity, skin of
forehead, nose, and eyes
2. The maxillary
•
From the lower eyelid, upper lip, cheek, nose, upper
gums, and teeth
3. The mandibular
•
© 2013 Pearson Education, Inc.
From salivary glands and tongue
The Cranial Nerves (8-8)
• The abducens nerves (N VI)
• Innervate only the lateral rectus extrinsic eye muscle,
with the nucleus in the pons
• The facial nerves (N VII)
• Mixed, and emerge from the pons
• Sensory fibers monitor proprioception in the face
• Motor fibers provide facial expressions; control tear and
salivary glands
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
•
The vestibulocochlear nerves (N VIII)
•
Respond to sensory receptors in the inner ear
•
There are two components
1. The vestibular nerve
•
Conveys information about balance and position
2. The cochlear nerve
•
•
© 2013 Pearson Education, Inc.
Responds to sound waves for the sense of hearing
Their nuclei are in the pons and medulla oblongata
The Cranial Nerves (8-8)
• The glossopharyngeal nerves (N IX)
• Mixed nerves innervating the tongue and pharynx
• Their nuclei are in the medulla oblongata
• The sensory portion monitors taste on the posterior third
of the tongue and monitors BP and blood gases
• The motor portion controls pharyngeal muscles used in
swallowing, and fibers to salivary glands
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
• The vagus nerves (N X)
• Have sensory input vital to autonomic control of the
viscera
• Motor control includes the soft palate, pharynx, and
esophagus
• Are a major pathway for ANS output to cardiac muscle,
smooth muscle, and digestive glands
© 2013 Pearson Education, Inc.
The Cranial Nerves (8-8)
• The accessory nerves (N XI)
• Have fibers that originate in the medulla oblongata
• Also in the lateral gray horns of the first five cervical
segments of the spinal cord
• The hypoglossal nerves (N XII)
• Provide voluntary motor control over the tongue
© 2013 Pearson Education, Inc.
Figure 8-25 The Cranial Nerves.
Olfactory bulb, termination
of olfactory nerve (I)
Olfactory tract
Optic chiasm
Optic nerve (II)
Mamillary
body
Basilar
artery
Infundibulum
Oculomotor nerve
(III)
Trochlear nerve
(IV)
Trigeminal nerve
(V)
Abducens nerve
(VI)
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Hypoglossal nerve
(XII)
Accessory nerve (XI)
Pons
Vertebral
artery
Cerebellum
Medulla
oblongata
Spinal cord
Inferior view of the brain
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Diagrammatic view showing
the attachment of the 12 pairs
of cranial nerves
Table 8-2 The Cranial Nerves
© 2013 Pearson Education, Inc.
The Spinal Nerves (8-8)
• Found in 31 pairs grouped according to the region
of the vertebral column
• 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
© 2013 Pearson Education, Inc.
Nerve Plexuses (8-8)
• The origin of major nerve trunks of the PNS
• The cervical plexus
• Innervates the muscles of the head and neck and the
diaphragm
• The brachial plexus
• Innervates the shoulder girdle and upper limb
• The lumbar plexus and the sacral plexus
• Innervate the pelvic girdle and lower limb
© 2013 Pearson Education, Inc.
Figure 8-26 Peripheral Nerves and Nerve Plexuses.
Cervical
plexus
Brachial
plexus
Lumbar
plexus
Sacral
plexus
C1
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T 10
T11
T12
Phrenic nerve (extends to the diaphragm)
Axillary nerve
Musculocutaneous
nerve
L1
Radial nerve
L2
Ulnar nerve
Median nerve
L3
L4
L5
S1
S2
S3
S4
S5
Co
1
Femoral nerve
Obturator nerve
Gluteal nerves
Saphenous nerve
Sciatic nerve
© 2013 Pearson Education, Inc.
Dermatome (8-8)
• A clinically important area monitored by a specific
spinal nerve
© 2013 Pearson Education, Inc.
Figure 8-27 Dermatomes.
C2–C3
NV
C2–C3
C2
C3
C3
T2
C6
L1
L2
C8
C7
T1
L3
L4
L5
C4
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
C4
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L4 L3
L5
C5
T2
C6
T1
C7
SS
S2
4 3
L1
S5
C8
S1 L5
L2 S2
L3
S1
L4
ANTERIOR
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POSTERIOR
Table 8-3 Nerve Plexuses and Major Nerves
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Checkpoint (8-8)
28. What signs would you associate with damage to the
abducens nerve (N VI)?
29. John is having trouble moving his tongue. His physician
tells him it is due to pressure on a cranial nerve. Which
cranial nerve is involved?
30. Injury to which nerve plexus would interfere with the
ability to breathe?
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Reflexes (8-9)
• Rapid, automatic, unlearned motor response to a stimulus
• Usually removes or opposes the original stimulus
• Monosynaptic reflexes
• For example, the stretch reflex
• Which responds to muscle spindles, is the simplest with only
one synapse
• The best known stretch reflex is probably the knee jerk reflex
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Simple Reflexes (8-9)
• Are wired in a reflex arc
• A stimulus activates a sensory receptor
• An action potential travels down an afferent neuron
• Information processing occurs with the interneuron
• An action potential travels down an efferent neuron
• The effector organ responds
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Figure 8-28 The Components of a Reflex Arc.
Arrival of
stimulus and
activation of
receptor
Stimulus
Activation of a
sensory neuron
Receptor
Dorsal
root
Sensation
relayed to the
brain by axon
collaterals
Information
processing
in the CNS
REFLEX
ARC
Effector
Response by
effector
Ventral
root
Activation of a
motor neuron
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KEY
Sensory
neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Figure 8-29 A Stretch Reflex.
Stretching of muscle tendon
stimulates muscle spindles
Stretch
Muscle spindle
(stretch receptor)
REFLEX
ARC
Spinal
Cord
Contraction
Activation of motor
neuron produces reflex
muscle contraction
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Complex Reflexes (8-9)
• Polysynaptic reflexes
• With at least one interneuron
• Are slower than monosynaptic reflexes, but can activate
more than one effector
• Withdrawal reflexes
• Like the flexor reflex, move a body part away from the
stimulation
• Like touching a hot stove
• Reciprocal inhibition
• Blocks the flexor's antagonist
• To ensure that flexion is in no way interfered with
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Figure 8-30 The Flexor Reflex, a Type of Withdrawal Reflex.
Distribution within gray horns to other
segments of the spinal cord
Painful
stimulus
Flexors
stimulated
Extensors
inhibited
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KEY
Sensory
neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Motor
neuron
(inhibited)
Inhibitory
interneuron
Input to Modify Reflexes (8-9)
• Reflexes are automatic, but higher brain centers
can influence or modify them
• The Babinski sign
• Triggered by stroking an infant's sole, resulting in a
fanning of the toes
• As descending inhibitory synapses develop, an adult will
respond by curling the toes instead, called the plantar
reflex
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Checkpoint (8-9)
31. Define reflex.
32. Which common reflex do physicians use to test the
general condition of the spinal cord, peripheral nerves,
and muscles?
33. Why can polysynaptic reflexes produce more involved
responses than can monosynaptic reflexes?
34. After injuring his back lifting a sofa, Tom exhibits a
positive Babinski reflex. What does this imply about
Tom's injury?
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Sensory Pathways (8-10)
• Are ascending pathways
• Posterior column pathway
• Spinothalamic pathway
• Spinocerebellar pathway
• A sensory homunculus
• A mapping of the area of the cortex dedicated to the
number of sensory receptors, not the size of the body
area
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Figure 8-31 The Posterior Column Pathway.
Sensory homunculus of
left cerebral hemisphere
KEY
Axon of firstorder neuron
Second-order
neuron
Third-order
neuron
Nuclei in
thalamus
MIDBRAIN
Nucleus in
medulla
oblongata
MEDULLA OBLONGATA
SPINAL CORD
Dorsal root
ganglion
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Fine-touch, pressure, vibration, and proprioception sensations from right side of body
Motor Pathways (8-10)
• Are descending pathways
• Corticospinal pathway
• Also called pyramidal system
• Medial and lateral pathways
• Also called extrapyramidal system
• A motor homunculus
• Represents the distribution of somatic and ANS motor
innervation
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Figure 8-32 The Corticospinal Pathway.
KEY
Axon of upper
motor neuron
Lower motor
neuron
Motor homunculus on primary motor
cortex of left cerebral
hemisphere
To skeletal
muscles
To skeletal
muscles
Motor nuclei
of cranial
nerves
MIDBRAIN
Motor nuclei
of cranial
nerves
MEDULLA OBLONGATA
Lateral
corticospinal
tract
To skeletal
muscles
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Anterior corticospinal tract
SPINAL CORD
Motor neuron in anterior gray horn
Table 8-4 Sensory and Motor Pathways
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Checkpoint (8-10)
35. As a result of pressure on her spinal cord, Jill cannot feel
touch or pressure on her legs. What sensory pathway is
being compressed?
36. The primary motor cortex of the right cerebral hemisphere
controls motor function on which side of the body?
37. An injury to the superior portion of the motor cortex
would affect the ability to control muscles of which parts
of the body?
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The Autonomic Nervous System (8-11)
• Unconscious adjustment of homeostatically essential
visceral responses
• Sympathetic division
• Parasympathetic division
• The somatic NS and ANS are anatomically different
• SNS: one neuron to skeletal muscle
• ANS: two neurons to cardiac and smooth muscle, glands, and fat
cells
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Two Neuron Pathways of the ANS (8-11)
• Preganglionic neuron
• Has cell body in spinal cord, synapses at the ganglion with the
postganglionic neuron
• In sympathetic division
• Preganglionic fibers are short
• Postganglionic fibers are long
• In parasympathetic division
• Preganglionic fibers are long
• Postganglionic fibers are "short"
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Figure 8-33 The Organization of the Somatic and Autonomic Nervous Systems.
Upper motor
neurons in
Primary
motor
cortex
Visceral motor nuclei in
hypothalamus
BRAIN
Somatic
motor nuclei
of brain stem
BRAIN
Preganglionic neuron
Visceral
Effectors
Smooth
muscle
Skeletal
muscle
Lower
motor
neurons
SPINAL
CORD
Glands
Cardiac
muscle
Somatic
motor
nuclei of
spinal cord
Autonomic
nuclei in
spinal cord
Adipocytes
Skeletal
muscle
Somatic nervous system
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Autonomic
ganglia
Ganglionic
neurons
Autonomic
nuclei in
brain stem
SPINAL CORD
Preganglionic
neuron
Autonomic nervous system
Neurotransmitters at Specific Synapses (8-11)
• All synapses between pre- and postganglionic fibers:
• Are cholinergic (ACh) and excitatory
• Postganglionic parasympathetic synapses
• Are cholinergic
• Some are excitatory, some inhibitory, depending on the receptor
• Most postganglionic sympathetic synapses:
• Are adrenergic (NE) and usually excitatory
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The Sympathetic Division (8-11)
• Sympathetic chain
• Arises from spinal segments T1–L2
• The preganglionic fibers enter the sympathetic chain
ganglia just outside the spinal column
• Collateral ganglia are unpaired ganglia that receive
splanchnic nerves from the lower thoracic and upper
lumbar segments
• Postganglionic neurons innervate abdominopelvic cavity
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The Sympathetic Division (8-11)
• The adrenal medullae
• Are innervated by preganglionic fibers
• Are modified neural tissue that secrete E and NE into
capillaries, functioning like an endocrine gland
• The effect is nearly identical to that of the sympathetic
postganglionic stimulation of adrenergic synapses
© 2013 Pearson Education, Inc.
Figure 8-34 The Sympathetic Division.
Eye
PONS
Salivary
glands
Sympathetic nerves
Cervical
sympathetic
ganglia
Heart
T1
T1
Spinal nerves
Cardiac and
Splanchnic pulmonary
nerve plexuses
Collateral
ganglion
Collateral
ganglion
Splanchnic
nerves
Postganglionic
fibers to spinal
nerves
(innervating skin,
blood vessels,
sweat glands,
arrector pili
muscles,
adipose tissue)
L2
Collateral
ganglion
L2
Lung
Liver and
gallbladder
Stomach
Spleen
Pancreas
Large
intestine
Small
intestine
Adrenal
medulla
Kidney
Sympathetic
chain ganglia
KEY
Preganglionic neurons
Ganglionic neurons
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Spinal cord
Uterus
Ovary Penis Scrotum Urinary bladder
The Sympathetic Division (8-11)
• Also called the "fight-or-flight" division
• Effects
• Increase in alertness, metabolic rate, sweating, heart
rate, blood flow to skeletal muscle
• Dilates the respiratory bronchioles and the pupils
• Blood flow to the digestive organs is decreased
• E and NE from the adrenal medullae support and
prolong the effect
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The Parasympathetic Division (8-11)
• Preganglionic neurons arise from the brain stem
and sacral spinal cord
• Include cranial nerves III, VII, IX, and X, the vagus,
a major parasympathetic nerve
• Ganglia very close to or within the target organ
• Preganglionic fibers of the sacral areas form the
pelvic nerves
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The Parasympathetic Division (8-11)
• Less divergence than in the sympathetic division,
so effects are more localized
• Also called "rest-and digest" division
• Effects
• Constriction of the pupils, increase in digestive secretions,
increase in digestive tract smooth muscle activity
• Stimulates urination and defecation
• Constricts bronchioles, decreases heart rate
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Figure 8-35 The Parasympathetic Division.
Terminal ganglion
N III
Lacrimal gland
Eye
Terminal ganglion
PONS
N VII
Terminal ganglion
N IX
N X (Vagus)
Salivary glands
Terminal
ganglion
Heart
Cardiac and
pulmonary
plexuses
Lungs
Liver and gallbladder
Stomach
Spleen
Pancreas
Large intestine
Pelvic
nerves
Small intestine
Rectum
Spinal
cord
Kidney
S2
S3
S4
KEY
Preganglionic neurons
Ganglionic neurons
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Urinary
bladder
Uterus Ovary Penis
Scrotum
Dual Innervation (8-11)
• Refers to both divisions affecting the same organs
• Mostly have antagonistic effects
• Some organs are innervated by only one division
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Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures
(1 of 2)
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Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures
(2 of 2)
© 2013 Pearson Education, Inc.
Checkpoint (8-11)
38. While out for a brisk walk, Megan is suddenly confronted
by an angry dog. Which division of the ANS is responsible
for the physiological changes that occur as she turns and
runs from the animal?
39. Why is the parasympathetic division of the ANS
sometimes referred to as the anabolic system?
40. What effect would loss of sympathetic stimulation have on
the flow of air into the lungs?
41. What physiological changes would you expect in a
patient who is about to undergo a root canal procedure
and is quite anxious about it?
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Aging and the Nervous System (8-12)
• Common changes
• Reduction in brain size and weight and reduction in
number of neurons
• Reduction in blood flow to the brain
• Change in synaptic organization of the brain
• Increase in intracellular deposits and extracellular
plaques
• Senility can be a result of all these changes
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Checkpoint (8-12)
42. What is the major cause of age-related
shrinkage of the brain?
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Figure 8-36
Body System
Provides sensations of touch, pressure,
pain, vibration, and temperature; hair
provides some protection and insulation
for skull and brain; protects peripheral
nerves
Controls contraction of arrector pili muscles
and secretion of sweat glands
Provides calcium for neural function;
protects brain and spinal cord
Controls skeletal muscle contractions
that results in bone thickening and
maintenance and determine bone
position
Facial muscles express emotional
state; intrinsic laryngeal muscles
permit communication; muscle
spindles provide proprioceptive
sensations
Controls skeletal muscle contractions;
coordinates respiratory and
cardiovascular activities
Integumentary
(Page 138)
Nervous System
Skeletal
(Page 188)
Integumentary
Skeletal
Muscular
Nervous System
Muscular
(Page 241)
SYSTEM INTEGRATOR
Body System
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Cardiovascular
(Page 467)
Lymphatic
(Page 500)
Respiratory
(Page 532)
Digestive
(Page 572)
Urinary
(Page 637)
Reproductive
(Page 671)
The nervous system is closely
integrated with other body systems.
Every moment of your life, billions
of neurons in your nervous system
are exchanging information
across trillions of synapses
and performing the most
complex integrative
functions in the body. As
part of this process, the
nervous system monitors all
other systems and issues
commands that adjust their
activities. However, the
impact of these commands
varies greatly from one
system to another. The normal
functions of the muscular system,
for example, simply cannot be
performed without instructions from the
nervous system. By contrast, the
cardiovascular system is relatively
independent—the nervous system
merely coordinates and adjusts
cardiovascular activities to meet the
circulatory demands of other systems. In
the final analysis, the nervous system is
like the conductor of an orchestra,
directing the rhythm and balancing the
performances of each section to
produce a symphony, instead of simply
a very loud noise.
Endocrine
(Page 376)
The NERVOUS System
Checkpoint (8-13)
43. Identify the relationships between the nervous
system and the body systems studied so far.
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