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ANATOMY AND
PHYSIOLOGY I
SEMINAR 7
CHAPTER 8
THE NERVOUS SYSTEM
RENITA K. HOLMES, MSN,
RN
KAPLAN UNIVERSITY
THE NERVOUS SYSTEM
The normal body must accomplish a gigantic and
enormously complex job—keeping itself alive and
healthy.
 Each one of its billions of cells performs some
activity that is a part of this function.
 Control of the body’s billions of cells is
accomplished in part by two body-wide
communication systems: the nervous system and
the endocrine system.
 Both systems transmit information from one part
of the body to another, but they do it in different
ways.

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THE NERVOUS SYSTEM
Nervous System
 Transmits information very rapidly by nerve
impulses conducted from one body area to
another.

Endocrine System
 Transmits information more slowly by chemicals
secreted by ductless glands into the bloodstream
and circulated from the glands to other parts of
the body.

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THE NERVOUS SYSTEM
 Nerve
impulses and hormones
communicate information to body
structures, increasing or decreasing their
activities as needed for healthy survival.
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THE NERVOUS SYSTEM
The nervous system is a complex network of
communication for the entire body.
 Chemical and electrical cell communication is
rapid, specific, and almost immediate
 Following are the three nervous system
integrated functions:
1.
Sensory input is when and how information
is gathered.
2.
Integration is when the sensory input is
deciphered.
3.
Motor output is the response caused by this
process.

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ORGANS AND DIVISIONS OF THE
NERVOUS SYSTEM (FIGURE 8-1)
 Central
nervous system (CNS)—brain
and spinal cord
 Peripheral nervous system (PNS)—all
nerves
 Autonomic nervous system (ANS)
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Divisions of the nervous system
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CELLS OF THE NERVOUS SYSTEM
 Neurons
 Consist
of three main parts
 Dendrites
 Cell body of neuron
 Axon
Dendrites conduct impulses to cell body of
neuron
 Axons conduct impulses away from cell
body of neuron

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CELLS OF THE NERVOUS SYSTEM
 Neurons
classified according to
function
Sensory (afferent) neurons: conduct impulses
to the spinal cord and brain
 Motor (efferent) neurons: conduct impulses
away from brain and spinal cord to muscles
and glands
 Interneurons: conduct impulses from sensory
neurons to motor neurons

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NEURON: DIAGRAM OF A TYPICAL NEURON
SHOWING DENDRITES, A CELL BODY, AND AN
AXON
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PHOTOMICROGRAPH OF A NEURON.
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CELLS OF THE NERVOUS SYSTEM

Glia (neuroglia)


Support cells, bringing the cells of nervous tissue
together structurally and functionally
Three main types of glial cells of the CNS (Figure 8-3)
Astrocytes—star-shaped cells that anchor small blood
vessels to neurons
 Microglia—small cells that move in inflamed brain tissue
carrying on phagocytosis
 Oligodendrocytes—form myelin sheaths on axons in the
CNS


Schwann cells form myelin sheaths on axons of the
PNS (Figure 8-2)
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Glia: A: Astrocytes have extensions attached to blood vessels in the brain.
B: Microglia within the central nervous system can enlarge and consume
microbes by phagocytosis.
C: Oligodendrocytes have extensions that form myelin sheaths around axons
in the central nervous system.
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NERVES AND TRACTS
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NERVES AND TRACTS
A
nerve is a group of peripheral
nerve fibers
(axons) bundled together like the strands
of a cable.
 Peripheral nerve fibers usually have a
myelin sheath; because myelin is white,
peripheral nerves often look white.
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NERVES AND TRACTS
(FIGURE 8-4)

Nerve—bundle of peripheral axons




Tract—bundle of central axons
White matter—tissue composed primarily of
myelinated axons (nerves or tracts)
Gray matter—tissue composed primarily of cell bodies
and unmyelinated fibers
Nerve coverings—fibrous connective tissue



Endoneurium—surrounds individual fibers within a
nerve
Perineurium—surrounds a group (fascicle) of nerve
fibers
Epineurium—surrounds the entire nervea
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The nerve: Each nerve contains axons bundled into fascicles. A connective tissue called
epineurium wraps the entire nerve. Perineurium surrounds each fascicle. Inset shows a scanning
electron micrograph of a cross section of a nerve.
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REFLEX ARCS
Nerve impulses are conducted from receptors to
effectors over neuron pathways or reflex arcs;
conduction by a reflex arc results in a reflex
(that is, contraction by a muscle or secretion by
a gland)
 The simplest reflex arcs are two-neuron arcs—
consisting of sensory neurons synapsing in the
spinal cord with motor neurons
 Three-neuron arcs consist of sensory neurons
synapsing in the spinal cord with interneurons
that synapse with motor neurons (Figure 8-5)

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Patellar reflex. The neural pathway involved in the
patellar (“knee-jerk”) reflex.
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NERVE IMPULSES
Definition—self-propagating wave of electrical
disturbance that travels along the surface of a
neuron membrane
 Mechanism
 A stimulus triggers the opening of Na+
channels in the plasma membrane of the
neuron
 Inward movement of positive sodium ions
leaves a slight excess of negative ions outside
at a stimulated point; marks the beginning of
a nerve impulse

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THE SYNAPSE
Definition—chemical compounds released from
axon terminals (of a presynaptic neuron) into a
synaptic cleft
 Neurotransmitters bind to specific receptor
molecules in the membrane of a postsynaptic
neuron, opening ion channels and thereby
stimulating impulse conduction by the
membrane
 Names of neurotransmitters—acetylcholine,
catecholamines (norepinephrine, dopamine, and
serotonin), and other compounds

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Components of a synapse.
Diagram shows synaptic knob or
axon terminal of presynaptic
neuron, the plasma membrane
of a postsynaptic neuron, and a
synaptic cleft. On the arrival of an
action potential at a synaptic knob,
neurotransmitter molecules are
released from vesicles in the knob
into the synaptic cleft.
The combining of neurotransmitter
and receptor molecules in the
plasma membrane of the
postsynaptic neuron opens ion
channels and thereby initiates
impulse conduction in the
postsynaptic neuron.
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CENTRAL NERVOUS SYSTEM

Divisions of the brain (Figure 8-9 and Table 8-1)

Brainstem
 Consists of three parts of brain; named in ascending
order: the medulla oblongata, pons, and midbrain
 Structure—white matter with bits of gray matter
scattered through it
 Function—gray matter in the brainstem functions as
reflex centers (e.g., for heartbeat, respirations, and
blood vessel diameter)
 Sensory tracts in the brainstem conduct impulses
to the higher parts of the brain
 Motor tracts conduct from the higher parts of the
brain to the spinal cord
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Central Nervous System
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CENTRAL NERVOUS SYSTEM

Divisions of the brain (cont.)

Diencephalon

Structure and function of the hypothalamus





Consists mainly of the posterior pituitary gland, pituitary
stalk, and gray matter
Acts as the major center for controlling the ANS; therefore, it
helps control the functioning of most internal organs
Controls hormone secretion by anterior and posterior pituitary
glands; therefore, it indirectly helps control hormone secretion
by most other endocrine glands
Contains centers for controlling body temperature, appetite,
wakefulness, and pleasure
Structure and function of the thalamus



Dumbbell-shaped mass of gray matter in each cerebral
hemisphere
Relays sensory impulses to cerebral cortex sensory areas
In some way produces the emotions of pleasantness or
unpleasantness associated with sensations
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CENTRAL NERVOUS SYSTEM

Divisions of the brain (cont.)

Cerebellum
Second largest part of the human brain
 Helps control muscle contractions to produce coordinated
movements so that we can maintain balance, move
smoothly, and sustain normal postures


Cerebrum
Largest part of the human brain
 Outer layer of gray matter is the cerebral cortex; made up
of lobes; composed mainly of dendrites and cell bodies of
neurons
 Interior of the cerebrum composed mainly of white matter
(that is, nerve fibers arranged in bundles called tracts)
 Functions of the cerebrum—mental processes of all types,
including sensations, consciousness, memory, and
voluntary control of movements

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CENTRAL NERVOUS SYSTEM

Spinal cord (Figure 8-11)
Outer part is composed of white matter made up of
many bundles of axons called tracts; interior
composed of gray matter made up mainly of neuron
dendrites and cell bodies
 Functions as the center for all spinal cord reflexes;
sensory tracts conduct impulses to the brain, and
motor tracts conduct impulses from the brain

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Spinal cord and
spinal nerves.
Inset is a dissection of
the cervical segment
of the spinal cord
showing emerging
cervical
nerves.
The spinal cord is
viewed from behind
(posterior aspect).
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CENTRAL NERVOUS SYSTEM

Coverings and fluid spaces of the brain and
spinal cord

Coverings
Cranial bones and vertebrae
 Cerebral and spinal meninges—the dura mater, the pia
mater, and the arachnoid mater (Figure 8-13)


Fluid spaces—subarachnoid spaces of meninges,
central canal inside cord, and ventricles in brain
(Figure 8-14)
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Spinal cord
The meninges,
spinal nerves, and
sympathetic
trunk are visible.
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Fluid spaces of the brain
A: The ventricles highlighted within the brain in a left lateral view.
B: The ventricles as seen from above.
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PERIPHERAL NERVOUS SYSTEM

Cranial nerves (Figure 8-16 and Table 8-2)



Twelve pairs—attached to undersurface of the brain
Connect brain with the neck and structures in the
thorax and abdomen
Spinal nerves


Structure—contain dendrites of sensory neurons
and axons of motor neurons
Functions—conduct impulses necessary for
sensations and voluntary movements
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Cranial nerves. View of the undersurface of the brain shows attachments of
the cranial nerves.
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AUTONOMIC NERVOUS SYSTEM
Autonomic nervous system—motor neurons that
conduct impulses from the central nervous
system to cardiac muscle, smooth muscle, and
glandular epithelial tissue; regulates the body’s
automatic or involuntary functions (Figure 8-18)
 Autonomic neurons—preganglionic autonomic
neurons conduct from spinal cord or brainstem
to an autonomic ganglion; postganglionic
neurons conduct from autonomic ganglia to
cardiac muscle, smooth muscle, and glandular
epithelial tissue

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Innervation of the major target organs by the autonomic nervous system.
The sympathetic pathways are highlighted with orange, and the parasympathetic
pathways are highlighted with green.
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AUTONOMIC NERVOUS SYSTEM
Autonomic or visceral effectors—tissues to
which autonomic neurons conduct impulses
(that is, cardiac and smooth muscle and
glandular epithelial tissue)
 Composed of two divisions—the sympathetic
system and the parasympathetic system

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Autonomic Nervous System
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AUTONOMIC NERVOUS SYSTEM

Autonomic conduction paths
 Consist of two-neuron relays (that is,
preganglionic neurons from the central
nervous system to autonomic ganglia,
synapses, postganglionic neurons from ganglia
to visceral effectors)
 In contrast, somatic motor neurons conduct all
the way from the CNS to somatic effectors
with no intervening synapses
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AUTONOMIC NERVOUS SYSTEM

Sympathetic nervous system

Structure
Dendrites and cell bodies of sympathetic
preganglionic neurons are located in the
gray matter of the thoracic and upper
lumbar segments of the spinal cord
 Axons leave the spinal cord in the anterior
roots of spinal nerves, extend to
sympathetic or collateral ganglia, and
synapse with several postganglionic
neurons whose axons extend to spinal or
autonomic nerves to terminate in visceral
effectors
 A chain of sympathetic ganglia is in front of
and at each side of the spinal column

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AUTONOMIC NERVOUS SYSTEM


Sympathetic nervous system
Functions
 Serves as the emergency or stress system,
controlling visceral effectors during
strenuous exercise and strong emotions
(anger, fear, hate, or anxiety)
 Group of changes induced by sympathetic
control is called the fight-or-flight response
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AUTONOMIC NERVOUS SYSTEM

Parasympathetic nervous system

Structure
 Parasympathetic preganglionic neurons have
dendrites and cell bodies in the gray matter of the
brainstem and the sacral segments of the spinal cord
 Parasympathetic preganglionic neurons terminate
in parasympathetic ganglia located in the head and
the thoracic and abdominal cavities close to visceral
effectors
 Each parasympathetic preganglionic neuron
synapses with postganglionic neurons to only one
effector
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AUTONOMIC NERVOUS SYSTEM
 Parasympathetic
nervous system
 Function—dominates
control of many
visceral effectors under normal, everyday
conditions
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AUTONOMIC NERVOUS SYSTEM
 Autonomic
neurotransmitters
Cholinergic fibers—preganglionic
axons of parasympathetic and
sympathetic systems and
parasympathetic postganglionic axons
release acetylcholine
 Adrenergic fibers—axons of
sympathetic postganglionic neurons
release norepinephrine (noradrenaline)

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AUTONOMIC NERVOUS SYSTEM
 Autonomic
nervous system as a whole
 Regulates the body’s automatic
functions in ways that maintain or
quickly restore homeostasis
 Many visceral effectors are doubly
innervated (that is, they receive fibers
from parasympathetic and sympathetic
divisions and are influenced in opposite
ways by the two divisions)
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AUTONOMIC NERVOUS SYSTEM
QUESTIONS?
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