140
UNIT 1
Organization of the Body
4
Nervous Tissue
Indicate the general characteristics of nervous tissue.
Nervous tissue is the main component of the nervous system—
the brain, spinal cord, and nerves—which regulates and con-
trols body functions. It contains two major cell types: neurons
and supporting cells.
Neurons
are highly specialized nerve cells that generate
and conduct nerve impulses
(Figure 4.10)
. Typically, they are
branching cells with cytoplasmic extensions or processes that
enable them to
Respond to stimuli (via processes called
dendrites
)
Transmit electrical impulses over substantial distances
within the body (via processes called
axons
)
Supporting cells are nonconducting cells that support, in-
sulate, and protect the delicate neurons. Chapter 11 presents a
more complete discussion of nervous tissue.
Check Your Understanding
18.
How does the extended length of a neuron’s processes aid its
function in the body?
For answers, see Appendix H.
Covering and Lining Membranes
Describe the structure and function of cutaneous, mucous,
and serous membranes.
Now that we have described all four primary tissues, we can
consider the body’s membranes that incorporate more than
one type of tissue. ±e covering and lining membranes are of
three types:
cutaneous
,
mucous
, or
serous.
Essentially they all are
continuous multicellular sheets composed of at least two pri-
mary tissue types: an epithelium bound to an underlying layer
of connective tissue proper. Hence, these membranes are simple
organs. We describe the
synovial membranes
, which line joint
cavities and consist of connective tissue only, in Chapter 8.
Cutaneous Membrane
±e
cutaneous
membrane
(ku-ta
9
ne-us;
cutis
5
skin) is your
skin
(Figure 4.11a)
. It is an organ system consisting of a
keratinized stratified squamous epithelium (epidermis) firmly
attached to a thick layer of connective tissue (dermis). Unlike
other epithelial membranes, the cutaneous membrane is ex-
posed to the air and is a dry membrane. Chapter 5 is devoted to
this unique organ system.
Photomicrograph:
Neurons (350
m
)
Function:
Neurons transmit electrical
signals from sensory receptors and to
effectors (muscles and glands) which
control their activity; supporting cells
support and protect neurons.
Location:
Brain, spinal
cord, and nerves.
Description:
Neurons are branching
cells; cell processes that may be quite
long extend from the nucleus-containing
cell body; also contributing to nervous
tissue are nonexcitable supporting cells.
Dendrites
Neuron processes
Cell body
Axon
Nuclei of
supporting
cells
Cell body
of a neuron
Neuron
processes
Nervous tissue
Figure 4.10
Nervous tissue.
(For a related image, see
A Brief Atlas of the Human Body
, Plate 33.)
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