peripheral nerves. As you can imagine, each of these
organs has very specific functions. For now, we will
just mention the categories of the functions of nerve
tissue. These include feeling and interpreting sensa-
tion, initiation of movement, the rapid regulation of
body functions such as heart rate and breathing, and
the organization of information for learning and
memory.
MEMBRANES
Membranesare sheets of tissue that cover or line sur-
faces or that separate organs or parts (lobes) of organs
from one another. Many membranes produce secre-
tions that have specific functions. The two major cat-
egories of membranes are epithelial membranes and
connective tissue membranes.EPITHELIAL MEMBRANES
There are two types of epithelial membranes, serous
and mucous. Each type is found in specific locations
within the body and secretes a fluid. These fluids are
called serous fluid and mucus.Serous Membranes
Serous membranesare sheets of simple squamous
epithelium that line some closed body cavities and
cover the organs in these cavities (Fig. 4–8). The
pleural membranesare the serous membranes of the
thoracic cavity. The parietal pleura lines the chest wall
and the visceral pleura covers the lungs. (Notice that
linemeans “on the inside” and covermeans “on the
outside.” These terms cannot be used interchangeably,
because each indicates a different location.) The pleu-
ral membranes secrete serous fluid, which prevents
friction between them as the lungs expand and recoil
during breathing.
The heart, in the thoracic cavity between the lungs,
has its own set of serous membranes. The parietal
pericardiumlines the fibrous pericardium (a connec-
tive tissue membrane), and the visceral pericardium,
or epicardium, is on the surface of the heart muscle
(see also Fig. 12–1). Serous fluid is produced to pre-
vent friction as the heart beats.
In the abdominal cavity, the peritoneumis the
serous membrane that lines the cavity. The mesen-
tery, or visceral peritoneum, is folded over and covers
the abdominal organs. Here, the serous fluid prevents
friction as the stomach and intestines contract and
slide against other organs (see also Fig. 16–4).Mucous Membranes
Mucous membranesline the body tracts (systems)
that have openings to the environment. These are the
respiratory, digestive, urinary, and reproductive tracts.
The epithelium of a mucous membrane (mucosa)
varies with the different organs involved. The mucosa
of the esophagus and of the vagina is stratified squa-
mous epithelium; the mucosa of the trachea is ciliated
epithelium; the mucosa of the stomach is columnar
epithelium.82 Tissues and Membranes
Figure 4–7. Nerve tissue of the central nervous system
(CNS).
QUESTION:How many processes does the central neu-
ron have, and what are they called?
Cell body
NeuronNeurons Nucleus(Approximately 250X)Neuroglia