HUMAN BIOLOGY

tIssUes, orGans, and orGan systeMs 73

FOCUS ON HEALTH

What is nervous tissue?

• Nervous tissue contains neurons, which are the body’s
  communication cells.


• Support cells called glia (neuroglia) make up most of the
  body’s nervous tissue.

taKe-hoMe Message

axon Neuron extension that

carries outgoing messages.

dendrite Neuron exten-

sion that receives incoming

messages.

glial cell Any of the cells

in the nervous system that

support neurons physically

or in other ways.

nervous tissue Tissue

made up of neurons and

glial cells.

neuron Nerve cell.

stem cells can give rise to various types of specialized

cells (inset). scientists in the field of regenerative medicine

commonly work with stem cells present in adult tissues

(such as skin), or present in blood remaining in the umbilical

cord after a baby is delivered. a major aim is to develop

therapies that help patients who suffer from parkinson’s

n    Nervous tissue makes up the nervous system.

The body’s nervous tissue consists mostly of neurons,

the “nerve cells,” and support cells. Tens of thousands of

neurons occur in the brain and spinal cord, and millions

more are present throughout the body. Neurons make up

the body’s communication lines. The signals they carry are

often called nerve impulses.

neurons carry messages

Like other kinds of cells, a neuron has a cell body that con-

tains the nucleus and cytoplasm. It also has two types of

extensions, or cell “processes.” Branched processes called

dendrites receive incoming messages. Processes called

axons conduct out going messages. Depending on the type

of neuron, its axon may be very short, or it may be as long

as three or four feet. In the image below (right), you can see

nervous tissue: Communication

regenerative Medicine

the cell processes of a motor neuron,

which carries signals to muscles

and glands.

neuroglia are support cells

About 90 percent of the cells in

the nervous system are glial cells

(also called neuroglia). The word glia

means “glue,” and glial cells were

once thought to simply be the “mor-

tar” that physically supported neu-

rons. Today we know that they have

various functions. In the central ner-

vous system, glia help supply nutrients to neurons, provide

physical support, and remove unwanted material. Outside

the brain and spinal cord glial cells provide insulation—

a function that helps speed nerve impulses through the

body, as described in Chapter 13.

disease, type 2 diabetes, sickle cell anemia, and paralysis

due to spinal cord injury.

Growing replacement tissues is another focus of

regenerative medicine. replacement tracheas (windpipes)

have been grown from adult stem cells seeded on a scaffold

of synthetic material. only a few patients have undergone

the procedure, which is still considered experimental. a

cultured skin substitute (Figure 4.6) now is a common option

for treating burns and chronic wounds. the tissue is grown

from cells extracted from foreskins removed when infant

boys are circumcised.

4.4

A motor neuron

Biophoto Associates/

Science Source

A glial cell

Nancy Kedersha/UCLA/Science Source

4.5

Figure 4.6 Stem cells from adult tissues and cord blood are

resources for regenerative medicine. A A cultured skin substitute

called Apligraf can be attached over a wound to help prevent

infection and speed up the healing process. B Stem cells from

umbilical cord blood.

Roberto A. Penne-

Casanova/Science Source SPL/Science Source

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