Muscle Power
Among the many additional muscles are those
of expression-small bundles of fibers around the eyes, mouth, and nose which we
use to look angry or surprised, to wink, sneer, smile, frown. In the
gastrointestinal system, there are voluntary muscles at the top, in the upper
part of the esophagus. But in the walls of the lower esophagus as well as most
of the stomach and intestines are involuntary muscles that help push food
along. Actually, there are two layers of such muscles which work in concert:
one, a circular layer, contracts to narrow the gastrointestinal tract; the
other, longitudinal, and contracts to widen the tract again and make way for
further narrowing.
Between the esophagus and the stomach, and
at other points in the digestive tract, are thick muscular rings, called
sphincters, which contract at intervals and can remain contracted for extended
periods if necessary to regulate the flow of food and liquid. MUSCLE TONE
Imagine for a moment that you have a rope fastened to a small wagon. In effect,
the rope is a tendon and the wagon is a movable bone. If you pull on the rope,
the wagon will move toward you. But if the rope is lying slack on the ground,
you first must pull it tight before the wagon can begin to move. If the rope is
kept taut, the wagon will move as soon as you pull. Most voluntary muscles of
the body keep their ropes tight, so to speak. They are partly contracted at all
times. Rarely, for example, does the jaw sag, and you can hold your head and
shoulders erect for hours without fatigue. This ability to maintain partial
contraction is muscle tone. Tone may be maintained, and the muscles prevented
from becoming slack and deteriorated, by regular exercise and proper nutrition.
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