Download 829 LB Muscle Power TG

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Muscle Power
Summary
This program uses sequences from a martial arts film to
dramatize the workings of voluntary muscles and contrast the
Kung Fu master’s strength and skill with his passive
audience—whose involuntary muscles are engaged in
ceaseless activities like blood circulation and digestion.
Muscles can produce powerful blows or the delicate movements of a pianist’s fingers. Both depend
on the ability of muscle cells to contract when so ordered.
There are two basic groups of muscle. Voluntary muscles are used for accuracy more often than
strength and can resist force as well as deliver it. Under the microscope, the muscle is seen to be
composed of millions of individual fibers that only contract when a message is received by the
bulbous nerve endings lying on the muscle’s surface. Muscle fibers usually contract many times per
second. Many muscle fibers pull in the same direction under the control of a few nerves; millions of
these tiny contractions add up to produce a steady force. A motor unit—a nerve and the muscle
fibers it controls—in the fingers may be as small as 10 fibers to one nerve; in the bigger muscles,
which need strength more than delicacy, a motor unit may be one nerve controlling hundreds of
muscle fibers. A muscle contraction occurs as strands of muscle fiber, set in an interlocking pattern,
telescope together to produce the contraction. To vary the strength of an individual muscle from
moment to moment, the number of fibers brought into action is altered.
Involuntary muscles are those beyond conscious control, although there are a few exceptions like
deliberately deep breathing. Completely involuntary muscle, or smooth muscle, exists in the heart
and blood vessels and in the digestive system. The camera shows individual heart cells beating on
their own. The muscles in blood vessels help maintain blood pressure as well as regulate blood flow
at certain important junctions, where they open and close like gates, sending blood down a
particular blood vessel or diverting it. The bladder walls also contain smooth muscle. People are
born with a fixed number of muscle fibers, but the size of muscle cells increases through growth.
Muscle movement expends energy, the chief source of which is food, especially carbohydrates.
Throughout the body, muscles and organs receive regular supplies of blood that carry glucose
stored in the liver and muscles. This glucose is “burned up” along with oxygen as muscles are used.
This process also generates heat, which is demonstrated by a special optical technique showing
heat waves radiating from an arm.
The muscles in and around the eyes control their direction and adjust the iris for the right amount
of light; the facial muscles allow for a wide variety of expressions including laughter.
Objectives
1. To explain the control of voluntary muscle by nerve endings located on its surface.
2. To show how muscle tissue contracts at the molecular level.
3. To describe the movements of involuntary muscle in various internal organs.
4. To examine the use of glucose and oxygen for energy by working muscles, and the by-product of
heat generated by muscular activity.
5. To show how the movement of the small, delicate muscles in the head and face makes us
distinctly human.
Recall Questions
1. Name the two muscle groups in the body. How is each controlled?
2. Define a motor unit.
3. Describe how muscles contract.
4. What are the substances “burned up” during muscle use, and where do they come from?
5. Why do people breathe heavily during and after strenuous physical activity?
Interpretive Questions
1. Give three examples from everyday life of contracting muscles resisting movement.
2. Would the human hand be as dexterous if its motor units were the same size as those of the
large thigh muscles? Explain your answer.
3. Describe some of the ways emotion is expressed by facial muscles. Why do you think only
mammals have facial muscles?
Vocabulary Required for Effective Viewing
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bladder
blood pressure
carbohydrates
contraction
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energy
• peristalsis
glucose
• tendons
intestines
• voluntary muscles
involuntary muscles
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