Chapter 13
Nerves of Steel
The Nervous System
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The Functions of the
Nervous System
• The nervous system coordinates and
controls body activity
• The nervous system detects and
processes internal and external
information and formulates
appropriate responses
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The Structures of the
Nervous System
• There are two major divisions of the
nervous system:
– The central nervous system (CNS)
consists of the brain and spinal cord
– The peripheral nervous system (PNS)
consists of the cranial and spinal
nerves, autonomic nervous system,
and ganglia
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The Structures of the
Nervous System
• The basic unit of the nervous system
is the neuron
• There are three types of neurons:
– sensory (also called afferent)
– associative
– motor (also called efferent)
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Parts of the Neuron
• The neuron consists
of
– a cell body (soma)
– dendrites
• Carry impulses
toward the cell
body
• Combining form is
dendr/o
– an axon
• Carries impulses
away from the cell
body
• Combining form is
ax/o
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The Gap
• The space between
two neurons or
between a neuron
and receptor is the
synapse
– The combining forms
for synapse are
synaps/o and synapt/o
– Chemical substances
called neurotransmitters are
released into the
space to allow
information to be
relayed
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Supporting Role
• Neuroglia or
glial cells are the
supportive cells
of the nervous
system
– The combining
form gli/o means
glue.
• Glial cells consist
of
–
–
–
–
–
astrocytes
microglia
ependymal cells
oligodendrocytes
Schwann cells
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Surrounding Structures
• Myelin is a protective
covering over some
nerve cells including
parts of the spinal
cord
• Myelin serves as an
electrical insulator
• Myelin is interrupted
at regular intervals
along the length of a
fiber by gaps called
nodes of Ranvier
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Nerves
• A nerve is one or more bundles of
impulse-carrying fibers that connect
the CNS to other parts of the body
• Combining forms for nerve or nerve
tissue are neur/i and neur/o
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The CNS
• The central nervous system is made
up of the brain and spinal cord
• The combining form for the brain is
encephal/o
• The combining form for the spinal
cord is myel/o (remember myel/o
also means bone marrow)
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The Meninges
• The meninges are a
three-layered
membrane that
surrounds the CNS
– The combining forms
for the meninges are
mening/o and
meningi/o
– The three layers of
the meninges are
the dura mater,
arachnoid membrane,
and the pia mater
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The CSF
• Cerebrospinal fluid (CSF) is the
clear, colorless ultrafiltrate that
nourishes, cools, and cushions the
CNS
• CSF is made by the choroid plexus
that lines the ventricles of the brain
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The Brain
• The brain is the
enlarged and
highly developed
portion of the
CNS that lies in
the skull and is
the main site of
nervous control
– The cranium is
the portion of
the skull that
encases the
brain
• crani/o is the
combining
form for skull
• encephal/o is
the combining
form for brain
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The Brain Divisions
• The brain is divided
into three main parts:
– Cerebrum is the
largest part and is
responsible for
receiving and
processing
information
• cerebr/o
– Cerebellum is the
second largest part
that coordinates
muscle activity
• cerebell/o
– Brainstem connects
the cerebral
hemispheres with
the spinal cord and
supports basic life
functions
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The Spinal Cord
•
The spinal cord is the
continuation of the
medulla oblongata of
the brainstem
– The combining form
for spinal cord is
myel/o
•
•
The spinal cord
passes through an
opening in the
occipital bone called
the foramen magnum
The spinal cord
carries the tracts that
influence the
innervation of the
limbs and lower part
of the body and is the
pathway for impulses
going to and from the
brain
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The Discs
• The spinal cord is housed
within vertebrae to protect
it from injury
• The vertebrae are
protected from each other
by intervertebral discs
located between the
vertebrae
• Intervertebral discs are
layers of fibrocartilage that
form pads separating and
cushioning the vertebrae
from each other
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The PNS
• The peripheral nervous system consists of cranial and
spinal nerves, the autonomic nervous system, and the
ganglia
– The cranial nerves are 12 pairs of nerves that originate from
the undersurface of the brain
– The spinal nerves arise from the spinal cord and supply
sensory and motor fibers to the body region associated with
their emergence from the spinal cord
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The ANS
• The autonomic nervous system is
that part of the peripheral nervous
system that innervates smooth
muscle, cardiac muscle, and glands
• There are two divisions of the ANS:
– sympathetic: fight or flight
– parasympathetic: maintains normal
body function
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Medical Terms for the
Nervous System
• Additional terms for nervous system
tests, pathology, and procedures can
be found in the text
• Review the Flash! CD program to
make sure you understand these
terms
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