Question

Define sliding filament theory of muscle contraction.

Answer 1

The sliding filament theory explains the process of muscle contraction during which the thin filaments slide over the thick filaments, which shortens the myofibril.



Each muscle fibre has an alternate light and dark band, which contains a special contractile protein, called actin and myosin respectively. Actin is a thin contractile protein present in the light band and is known as the I-band, whereas myosin is a thick contractile protein present in the dark band and is known as the A-band. There is an elastic fibre called z line that bisects each I-band. The thin filament is firmly anchored to the z line. The central part of the thick filament that is not overlapped by the thin filament is known as the H-zone.

Answer 2

Sliding filament theory of muscle contraction:

• This theory illustrates, mechanism of how muscle contraction, based on muscle proteins, produces force and slides past each other to generate movement.
• Myofibrils form muscle fibres and comprise of sarcomeres, that carry actin and myosin.

• When a nerve impulse reaches the neuromuscular junction, it releases acetylcholine.
• Now the myosin heads attach to the exposed actin-binding sites and form a cross – bridge. Energy is released from ATP by hydrolysis, which allows myosin to its head, to create an overlap by pulling actin.
• ATP binds to myosin heads and causes the 'cross-bridge' to break. The ATP once hydrolyzed can bind to another actin-binding site.
• This allows contraction to continue further.
• Lastly, when ATP and $\mathrm{Ca} 2+$ get depleted in the muscle, contraction terminates. Acting binding sites are again covered with tropomyosin.

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