APBIO muscle contraction
Describe how the muscle contraction works by using sliding theory in a molecular level. You must specifically explain how specific things interact with one another to form the contraction.
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According to sliding-filament theory, the two kinds of filaments slide past each other so as to produce change in the length of the voluntary muscle. It has been found that during both contraction and stretching, the length of A-bands remains constant and the length of the I-bands changes in accordance with the length of the muscle. Since the length of the A-band is equal to the length of the thick filaments, so the length of these filaments, also remain constant. But the length of H-zone increases or decreases with the length of the I-band, so that the distance from the end of one H-zone through the Z-line to the beginning of the next H-zone remains almost the same.
The “Sliding-Filament Theory of Muscle Action” explains how the movement of thick and thin filaments relative to each other leads to the contraction and relaxation of whole muscles. There are two physical units that are important for the action of muscles: thick filament and thin filaments. Muscle tissues can be described in terms of units called sacromere. These units are defined in terms of groups of overlapping filaments (thick and thin filaments). The length of a sacromere and the zones within each sacromere (H zone, I band, and A band) are determined by the positions of the thick and thin filaments relative to each other. This sliding filament mechanism can only occur when there are sufficient calcium ions and ATP.
During Muscle Contraction, the myosin heads on the thick filaments "hook" onto, and so pull, the thin filaments towards the centre, which is "M-line", of each sacromere. As the thin filaments slide over the thick filaments, the I bands and H zones becomes narrower and narrower until they disappear when the muscle reaches its fully contracted state.
During Muscle Relaxation, the myosin heads release their hold on the thin filaments when the myosin heads on the thick filaments relax, thereby allowing them to slide back to their "relaxed" positions in which the I bands and H zones appear again.
This leads to questions about what causes the myosin heads to lock onto the thin filaments and pull them, and what causes them to relax and release their hold on the thin filaments. These processes happen as a result of instructions sent via the nervous system to activate and deactivate these tissues. The muscular and nervous systems are connected to each other by neuromuscular junctions.
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