THE HUMAN MUSCULAR SYSTEM
Muscular tissue is useful to the body because it contracts and thereby produces
movement. The contraction of striated muscle attached to bone results in movement of
the skeleton. Cardiac muscle contracts rhythmically and acts as a pump to move blood
through the cardiovascular system. The contraction of smooth or visceral muscle
results in the movement of materials inside the body, such as the propulsion of food
through the digestive tract.
2-2. TERMS ASSOCIATED WITH THE HUMAN MUSCULAR SYSTEM
a. Motor Unit. A motor unit is a single motor neuron and the number of striated
muscle fibers activated by it (innervation). The importance of the motor unit is that its
fibers work in unison.
b. Tonus. Tonus is defined as a slight continuous contraction of muscle tissue
that aids in the maintenance of posture and in the return of blood to the heart.
c. All or None Law. Under the influence of nervous stimulation, a single
muscle fiber will always contract to its maximum capacity.
2-3. PROPERTIES OF MUSCLE TISSUE
Muscles have certain key properties:
Irritability. Irritability refers to the ability of a muscle to respond to a stimulus.
Contractability. Contractability refers to the muscle's ability to shorten in
Extensibility. Extensibility refers to a muscle's ability to extend in length.
d. Elasticity. Elasticity refers to a muscle's ability to stretch and return to its