Neuronal Signaling and the Structure of the Nervous System
173
SECTION C REVIEW QUESTIONS
1. Contrast the postsynaptic mechanisms of excitatory and
inhibitory synapses.
2. Explain how synapses allow neurons to act as integrators;
include the concepts of facilitation, temporal and spatial
summation, and convergence in your explanation.
Figure 6–37
Overview of the structural and functional organization of the nervous system.
SECTION D
Structure of the Nervous System
We now survey the anatomy and broad functions of the major
structures of the central and peripheral nervous systems.
Figure 6–37
provides a conceptual overview of the organiza-
tion of the nervous system for you to refer to as we discuss the
various subdivisions in this section and in later chapters.
First, we must deal with some potentially confusing ter-
minology. Recall that a long extension from a single neuron is
called an axon or a nerve fi ber and that the term
nerve
refers to
a group of many axons that are traveling together to and from
the same general location in the peripheral nervous system.
There are no nerves in the central nervous system. Rather, a
group of axons traveling together in the central nervous sys-
tem is called a
pathway,
a
tract,
or, when it links the right
and left halves of the central nervous system, a
commissure.
Information can pass through the central nervous sys-
tem down
long neural pathways
. In these pathways, neurons
with long axons carry information directly between the brain
and spinal cord or between large regions of the brain. In addi-
tion, information can travel through multisynaptic pathways
made up of many neurons and many synaptic connections.
Because synapses are the sites where new information can be
integrated into neural messages, there are many opportunities
for neural processing along the multisynaptic pathways. The
long pathways, on the other hand, consist of chains of only a
Peripheral nervous system
Afferent division
Efferent division
Special sensory
Somatic sensory
Somatic motor
Autonomic motor
Sympathetic
Parasympathetic
Enteric
Visceral sensory
Central nervous system
Brain
Spinal
cord
3. List at least eight ways in which the effectiveness of synapses
may be altered.
4. Discuss differences between neurotransmitters and
neuromodulators.
5. Discuss the relationship among dopamine, norepinephrine,
and epinephrine.
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