Textbook Question
Compare these images of a relaxed skeletal muscle fiber and a fully contracted muscle fiber. Which would you see only in the relaxed fiber?
a. Z discs
b. Sarcomeres
c. I bands
d. A bands
e. H zones
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9. Muscle Tissue
Sliding Filament Theory and the Sacromere
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During a muscle contraction, what happens to the actin and myosin filaments according to the sliding filament theory?
A
Actin and myosin filaments shorten to produce contraction.
B
Actin filaments slide past myosin filaments, shortening the sarcomere.
C
Myosin filaments slide past actin filaments, lengthening the sarcomere.
D
Both actin and myosin filaments remain stationary, and the sarcomere lengthens.
Verified step by step guidance1
Understand the basic structure of a sarcomere, which is the functional unit of a muscle fiber, composed of actin (thin) and myosin (thick) filaments.
Familiarize yourself with the sliding filament theory, which explains how muscle contraction occurs at the molecular level.
According to the sliding filament theory, during muscle contraction, the actin filaments slide past the myosin filaments.
This sliding action causes the sarcomere, the segment of the muscle fiber, to shorten, leading to muscle contraction.
Note that the filaments themselves do not shorten; instead, their relative positions change, resulting in the shortening of the sarcomere.
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