Neurons

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Cells of the Nervous System
Cells of the Nervous System
䉴 What are neurons, and what do they do?
We begin by considering the nervous system, a vast network of cells that tells you
what is going on inside and outside your body and allows you to make appropriate
responses. For example, if you are jabbed with a pin, your nervous system gets the message and immediately causes you to flinch. But the nervous system can do far more
than detect information and make responses. When information about the world
reaches the brain, that information is processed—it is combined with information about
past experiences and current wants and needs—to allow you to make a decision about
how to respond (see Figure 2.1). We begin our exploration of the nervous system at
the “bottom,” with a description of its individual cells. Later we consider how these cells
are organized to form the structures of the human nervous system.
Neurons
As Figure 2.1 shows, the nervous system is actually an information-processing system with
three functions: input, processing, and output. These functions are possible partly because
the nervous system is made up of cells that communicate with each other. Two major types
of cells, neurons and glial cells, allow the nervous system to carry out its complex signaling tasks efficiently. The specialized cells that send and receive signals are called neurons.
Most of our discussion of brain cells concerns neurons, but glial cells are important,
too. Glial means “glue,” and scientists had long believed that glial cells did no more than
hold neurons together. We now know, however, that glial cells also help neurons communicate by directing their growth, keeping their chemical environment stable, providing energy, secreting chemicals to help repair damage, and even responding to signals
from neurons (Fellin et al., 2004). Without glial cells, neurons could not function, and
recent research suggests that malfunctions in glial cells may play a role in problems ranging from recurring pain to depression and other mental disorders (Miller, 2005a).
FIGURE 2 .1
Three Functions of the Nervous
System
The nervous system’s three main functions
are to receive information (input), to
integrate that information with past
experiences (processing), and to guide
actions (output). When the alarm clock
goes off, this person’s nervous system,
like yours, gets the message, recognizes
what it means, and takes action—by getting out of bed or perhaps hitting the
snooze button.
nervous system A network of billions
of cells that detects what is going on
inside or outside the body and guides
appropriate responses.
neurons Specialized cells of the
nervous system that send and receive
messages.
glial cells Nervous system cells that
hold neurons together and help them
communicate with each other.
1. Input
The sound of
the alarm clock
is conveyed to
your brain by
your ears.
2. Processing
Your brain
knows from
past experience
that it is time
to get up.
3. Output
Your brain
directs the
muscles of your
arm and hand to
reach out and
shut off the
alarm clock.