Question

Explain the mechanism of muscle contraction.

OR

Explain the Sliding filament theory .

Answer 1

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According to the sliding filament theory, the actin (thin) filaments of muscle fibers slide past the myosin (thick) filaments during muscle contraction, while the two groups of filaments remain at relatively constant length.

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Answer 2

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¤¤ According to this Theory, "Contraction Of Muscle Fibre occurs by the slidding of actin over the myosin".

▪▪ This Mechanism Included following Steps :-

¤¤ An Impulse from the CNS reaches the Neuromuscular junction via motor neurons.
Neuromuscular junction is the synapse between a motor neuron and sarcolemma of tje muscle fibres.

¤¤ The synaptic vesicles releases a neurotransmitter [ Acetylcholine ]. It generates an Action potential in sarcolemma. It spreads through the muscles fibres and cause the releases of calcium ions into the sarcoplasm.

¤¤ Calcium Ions binds with a subunits of troponin on actin filament and removes the masking of active sites for myosin.

¤¤ Using Energy from ATP hydrolysis, myosin head bind to exposed active sites on the actin to form a cross bridge. This pulls actin filaments on both sides towards the centre of A-bands. The Actin filaments partially overlap so that H-zone disappears.

¤¤ The Z-line attached to actins is also pulled inward causes a shortening of sarcomere.

¤¤ I-bands get shortened, whereas A-bands retain the length.

¤¤ Myosin releases ADP and Inorganic phosphate and goes back to its relaxed state. A new ATP binds and the cross bridge is broken.

¤¤ The ATP is against hydolysed by the myosin head and above process is repeated causing further sliding.

¤¤ When Calcium ions are pumped back to sarcoplasmic cisternae, actin filaments are again masked. This causes the return of Z-Lines back to their original position. It results in Relaxation.


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