Multiple Choice
In the context of sliding filament theory, what is the basic contractile unit of a skeletal muscle fiber?
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9. Muscle Tissue
Sliding Filament Theory and the Sarcomere
Multiple Choice
In sliding filament theory, which band shortens during sarcomere contraction?
A
A band
B
I band
C
Z disc
D
M line
Verified step by step guidance1
Understand the structure of a sarcomere, which is the functional unit of muscle contraction. It consists of different bands and lines: the A band, I band, Z disc, and M line.
Recall that the A band corresponds to the length of the thick filaments (myosin) and does not change length during contraction because thick filaments remain the same size.
Know that the I band contains only thin filaments (actin) and is the region that shortens as the thin filaments slide over the thick filaments during contraction.
Recognize that the Z disc marks the boundary between adjacent sarcomeres and moves closer together during contraction, but it is not a band that shortens itself.
Conclude that the I band shortens during sarcomere contraction because it is the region where only thin filaments are present and their overlap with thick filaments increases.
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