Correct order of stages of muscle contraction is A Stimuli Neurotransmitter secretion → Release of calcium → Cross-bridges formation → Excitation of T-system → Sliding of actin filament B Stimuli Neurotransmitter secretion → Excitation of T-system → Release of C a 2 + → Cross-bridges formation → Sliding of actin filaments → H band diminishes C Stimuli Excitation of T-system → Neurotransmitter secretion → Crossbridges formation → Sliding of actin filaments → H band diminishes D Stimuli → Neurotransmitter secretion → Cross-bridges formation → Excitation of T-system → Sliding of actin filaments

Question

ankit singh · Answer

Active sites for myosin(Thick filament) are present on actin which are masked by troponin-C in resting state. when Ca++ level increases it leads to the binding of calcium with a subunit of troponin i.e Troponin-C on actin(thin) filaments and thereby remove the masking of active sites for myosin.
Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
This pulls the attached actin filaments towards the center of ‘A’ band.
The ‘Z’ line attached to these actins are also pulled inwards thereby causing a shortening of the sarcomere, i.e., contraction. Hence the ‘I’ band and 'H' band get reduced, whereas the ‘A’ bands retain the length.

So, Correct answer is 'Stimuli Neurotransmitter secretion →→ Excitation of T-system →→ Release of Ca
2
+ →→ Cross-bridges formation →→ Sliding of actin filaments →→ H band diminishes'

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Correct order of stages of muscle contraction is

Stimuli Neurotransmitter secretion → Release of calcium → Cross-bridges formation → Excitation of T-system → Sliding of actin filament

Stimuli Neurotransmitter secretion → Excitation of T-system → Release of Ca2+ → Cross-bridges formation → Sliding of actin filaments → H band diminishes

Stimuli Excitation of T-system → Neurotransmitter secretion → Crossbridges formation → Sliding of actin filaments → H band diminishes

Stimuli → Neurotransmitter secretion → Cross-bridges formation → Excitation of T-system → Sliding of actin filaments

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