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Structure of Skeletal Muscle

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Question

What happens to the I band and H zone during contraction? Do the lengths of the thick and thin filaments change?

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Solution

The formation of the cross-bridges pulls the actin filament towards the centre of the A-band. The Z-line attached to this actin is also pulled inwards thereby causing a shortening of the sarcomere i.e. contraction occurs. The thin myofilaments move past the thick myofilaments due to which the H- zone narrows. This, in turn, reduces the length of the I band but retains the length of A band.
The thick and the thin filaments refer to the actin and myosin filaments respectively. No, their lengths do not change but instead, they slide over each other.

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Similar questions

Q. During contraction, what changes would you expect to see in the various lines, bands, and zones of the sarcomere, on the basis of the sliding filament hypothesis?

Q. Identify the correct statements.

1. A-bands are dark and contain myosin.
2. I-bands are light and contain actin.
3. During the action, A band contracts.
4. The part between two Z-lines is sarcomere.
5. The central part of thin filament, not overlapped by thick filament is the H-zone.

Q. Select true or false
i. Shortening of sarcomere occurs when Z lines attached to actin filaments are pushed outwards.
ii. During contraction, I bands retain their lengths.
iii. During contraction, A bands get reduced in length.

Q. Value based questions.
Explain how any change in the A, H and I band lengths are brought about in terms of what happens to the actin and myosin filaments.

Q. Assess the statements.
1. A-bands of the muscle is dark and contain myosin.
2. I-bands are the light bands and contain actin.
3. During muscle contraction the A-band contracts.
4. The part between the two Z-lines is called as sarcomere.
5. The central part of thick filament, not overlapped by thin filament, called H-zone.
Of the above statements.

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