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Nervous System
Chapter 9
Copyright © 2016 by Elsevier Inc. All rights reserved.
1
Learning Objectives
Lesson 9.1: Nervous System
1.
2.
3.
4.
List the organs and divisions of the nervous
system and describe the generalized
functions of the system as a whole.
Identify the major types of cells in the
nervous system and discuss the functions of
each.
Identify the anatomical components of a
reflex arc and explain its function.
Explain the mechanisms of transmission of a
nerve impulse along a nerve fiber and across
a synapse.
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2
Learning Objectives
Lesson 9.1: Nervous System (Cont.)
5.
6.
7.
Identify the major anatomical components of
the brain and spinal cord and briefly
comment on the functions of each.
Compare and contrast cranial and spinal
nerves.
Discuss the anatomical and functional
characteristics of the two divisions of the
autonomic nervous system.
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Organization of the Nervous System

Central nervous system (CNS)



Brain
Spinal cord
Peripheral nervous system (PNS)


All nerves
Autonomic nervous system (ANS)
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4
Divisions of the Nervous System
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Cells of the Nervous System

Neurons

Neuron structure: Each neuron consists of three main parts
(Figure 9-2):
•
•
•

Cell body of neuron
Dendrites: Branching projections that conduct impulses to cell
body of neuron
Axon: Elongated projection that conducts impulses away from
cell body of neuron
Types of 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 or among a network of interneurons; also known as
central or connecting neurons
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Neuron
Courtesy Dennis Streete.
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Nerves and Tracts

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 nerve
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The Nerve
Courtesy Dr. Richard Kessel, Professor of Biological Sciences, University of Iowa, Iowa City.
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9
Knee-Jerk Reflex
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Central Nervous System

Divisions of the brain: Brainstem

Consists of three parts of brain, named in ascending
order
•
•
•

Structure
•

Medulla oblongata
Pons
Midbrain
White matter with bits of gray matter scattered through it
Functions
•
All three parts of brainstem conduct impulses to the higher
parts of the brain


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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Major Regions of the
Central Nervous System
From Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.
Copyright © 2016 by Elsevier Inc. All rights reserved.
12
Functions of Major Division of the Brain
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13
Central Nervous System (Cont.)

Divisions of the brain: Cerebellum

Structure
•
•
•

Second largest part of the human brain
Gray matter outer layer is thin but highly folded, forming
a large surface area for processing information
Arbor vitae: Internal, treelike network of white matter
tracts
Functions
•
•
Helps control muscle contractions to produce
coordinated movements for maintaining balance, moving
smoothly, and sustaining normal postures
Variety of additional coordinating effects, assisting the
cerebrum and other regions of the brain
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Central Nervous System (Cont.)

Divisions of the brain: Diencephalon
(hypothalamus, thalamus, and pineal gland)

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
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Central Nervous System (Cont.)

Divisions of the brain: Diencephalon
(hypothalamus, thalamus, and pineal gland)

Thalamus
•
•
•

Dumbbell-shaped mass of gray matter extending toward
each cerebral hemisphere
Relays sensory impulses to cerebral cortex sensory
areas
In some way produces the emotions of pleasantness or
unpleasantness associated with sensations
Pineal gland (pineal body)
•
•
Small body resembling a pine nut behind the thalamus
Adjusts output of “time-keeping hormone” melatonin in
response to changing levels of external light (sunlight
and moonlight)
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Central Nervous System (Cont.)

Divisions of the brain: Cerebrum (Figure 9-11)



Largest part of the human brain
Outer layers of gray matter are 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
•
•

Tracts: Nerve fibers arranged in bundles
Basal nuclei: Islands of gray matter regulate automatic
movements and posture
Functions of the cerebrum
•
Mental processes of all types, including sensations,
consciousness, memory, and voluntary control of
movements
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The Cerebrum
From Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.
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18
The Cerebrum (Cont.)
From Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.
Copyright © 2016 by Elsevier Inc. All rights reserved.
19
Central Nervous System (Cont.)

Spinal cord (Figure 9-12)




Columns of white matter, composed of bundles of
myelinated nerve fibers, form the outer portion of
the H-shaped core of the spinal cord; bundles of
axons called tracts
Interior composed of gray matter made up mainly
of neuron dendrites and cell bodies
Spinal cord tracts provide two-way conduction
paths: Ascending and descending
Spinal cord functions as the primary 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
From Vidic B, Suarez FR: Photographic atlas of the human body, St Louis, 1984, Mosby.
Copyright © 2016 by Elsevier Inc. All rights reserved.
21
Central Nervous System (Cont.)

Coverings (Figure 9-14)


Cranial bones and vertebrae
Cerebral and spinal meninges
•
•
•

Dura mater
Pia mater
Arachnoid mater
Fluid spaces



Subarachnoid spaces of meninges
Central canal inside cord
Ventricles in brain
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Spinal Cord and Its Coverings
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Peripheral Nervous System

Cranial nerves (Figure 9-17 and Table 9-2)



Twelve pairs: Attached to undersurface of the brain
Connect brain with the neck and structures in the
thorax and abdomen
Spinal nerves



Thirty-one pairs: Contain dendrites of sensory
neurons and axons of motor neurons
Conduct impulses necessary for sensations and
voluntary movements
Dermatome: Skin surface area supplied by a single
cranial or spinal nerve
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Cranial Nerves
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Cranial Nerves (Cont.)
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Autonomic Nervous System


ANS consists of motor neurons that conduct
impulses from the CNS to cardiac muscle,
smooth muscle, and glandular epithelial tissue;
regulates the body’s automatic or involuntary
functions (Figure 9-19)
Functional anatomy:


Preganglionic autonomic neurons conduct impulses
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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Autonomic Nervous System (Cont.)


Functional anatomy: Autonomic or visceral
effectors are the tissues to which autonomic
neurons conduct impulses (i.e., cardiac and
smooth muscle and glandular epithelial tissue)
Composed of two divisions


Sympathetic system
Parasympathetic system
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Innervation of Major Target Organs
by the Autonomic Nervous System
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Autonomic Nervous System (Cont.)

Autonomic conduction paths


Consist of two-neuron relays (that is,
preganglionic neurons from the CNS 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 (Cont.)

Sympathetic division: 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 (Cont.)

Sympathetic division: Functions


Serves as the emergency or stress system,
controlling visceral effectors during strenuous
exercise and when strong emotions (anger, fear,
hate, or anxiety) are triggered
Group of changes induced by sympathetic control
is called the fight-or-flight response
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Autonomic Nervous System (Cont.)

Parasympathetic division: Structure

Parasympathetic preganglionic neurons
•
•
•
Have dendrites and cell bodies in the gray matter of the
brainstem and the sacral segments of the spinal cord
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
 Parasympathetic


division: Functions
Dominates control of many visceral effectors under
normal, everyday conditions
Counterbalances sympathetic function
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Autonomic Nervous System (Cont.)

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 (Cont.)

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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