The major functions of the nervous system are to detect, analyze,
and transmit information. Information is gathered by sensory systems,
integrated by the brain, and used to generate signals to motor and
autonomic pathways for control of movement and of visceral and endocrine
functions. These actions are controlled by neurons, which are interconnected
to form signaling networks that comprise motor and sensory systems. In
addition to neurons, the nervous system contains neuroglial cells
that serve a variety of immunologic and support functions and modulate
the activity of neurons. Understanding the pathophysiology of nervous
system disease requires knowledge of neural and glial cell biology
and the anatomy of neural networks. The first part of this chapter
reviews several basic aspects of histology, cellular physiology,
and anatomy of the nervous system.
Understanding the causes of neurologic diseases requires knowledge
of molecular and biochemical mechanisms. Discoveries in the fields
of molecular biology and genetics have made available important
information about the mechanisms of several disease states. Several
neurologic disorders in which some of the molecular mechanisms of
pathogenesis are known are discussed later in this chapter including
motor neuron disease, Parkinson’s disease, myasthenia gravis,
epilepsy, Alzheimer’s disease, and stroke. Exciting advances
in our understanding and overlap of these diseases are leading to
new therapeutic targets and the hope of better treating these devastating
The major function of neurons is to receive, integrate, and transmit
information to other cells. Neurons consist of three parts: dendrites, which
are elongated processes that receive information from the environment
or from other neurons; the cell body, which contains
the nucleus; and the axon, which may be up to 1 m long
and conducts impulses to muscles, glands, or other neurons (Figure 7–1). Most neurons are multipolar,
containing one axon and several dendrites. Bipolar neurons have
one dendrite and one axon and are found in the cochlear and vestibular
ganglia, retina, and olfactory mucosa. Spinal sensory ganglia contain
pseudounipolar neurons that have a single process that emanates
from the cell body and divides into two branches, one extending
to the spinal cord and the other extending to the periphery. Axons
and dendrites usually branch extensively at their ends. Dendritic
branching can be very complex, with the result that a single neuron
may receive thousands of inputs. Axon branching allows several target
cells to simultaneously receive a message from one neuron. Each
branch of the axon terminates on the next cell at a synapse, which
is a structure specialized for information transfer from the axon
to muscle, to glands, or to another neuron. Synapses between neurons
most often occur between axons and dendrites but may occur between
an axon and a cell body, between two axons, or between two dendrites.
Schematic drawing of a Nissl-stained motor neuron. ...
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