PHYSIOLOGY AND ACTIONS OF MUSCLES
Section I. MUSCLE TISSUES
The term muscle (like the term bone) is used with two distinctly different
meanings. In one case, the term is used to designate tissues. In the other case, the
term refers to individual, discrete organs of the body. However, the structure and
actions of tissues are often quite different in detail from the structure and actions of
5-2. ACTIONS OF MUSCLE TISSUES
a. Tissues of the body are collections of like cells performing a common
function. Muscle tissues are specialized to produce tension by contraction. In fact, they
function solely by contraction.
b. As a by-product, muscle tissues also produce heat. (Shivering is a state in
which the muscles of the body are primarily concerned with producing heat. Shivering
involves contractions that are not synchronized and therefore do not produce motion.)
c. As used in muscle physiology, the term contraction is not necessarily
synonymous with the term shortening. Rather, contraction means the production of
tension through the interaction of the muscle tissues.
5-3. TYPES OF MUSCLE TISSUES
There are three types of muscle tissue:
a. Smooth. Smooth muscle tissue consists of elongated cellular elements. It is
found mainly in the walls of visceral organs and blood vessels.
b. Striated. Striated muscle tissue is composed of fibers. These fibers
represent the fusion of many cells into a single functioning fiber (syncytium). Under the
microscope, these fibers appear to have a transverse pattern of light and dark banding.
c. Cardiac. Cardiac muscle tissue is also composed of banded fibers.
However, its fibers have a branched character. Cardiac muscle tissue is found only in
the wall of the heart.