Question

Calcium release due to sarcoplasmic reticulum stimulation happens during _____.

	a.	Contraction phase
	b.	Recharge phase
	c.	Resting phase
	d.	Excitation-contraction coupling phase

Answer 1

Calcium release due to sarcoplasmic reticulum stimulation happens during EXCITATION CONTRACTION COUPLING PHASE.

So, answer is option d.

Excitation contraction coupling phase is a series of events which occurs after arrival of action potential at sarcolemma because of neurotransmitter release by an axon terminal and calcium ions release from sarcoplasmic reticulum because of propagation of action potential to the interior of muscle fibres by T cells.

When acetylcholine is released from an axon end,it gets diffused into the muscle cell and then it attaches to Ach receptors which are already present on sarcolemma.Then, Depolarisation occurs leading to generation of action potential all along sarcolemma,This action potential goes deep into the cell via T tubules ,which eventually causes sarcoplasmic reticulum to release calcium ions.Then the concentration of calcium increases at myofilaments and myofilaments past slide one another and there will be shortening of the cell. When action potential ends within a span of approximately 30 milliseconds,at the myofilaments calcium concentration will decrease which again cause muscle cell to get relax and lengthen.

Excitation in more simple way means depolarization and action potential which is spreading along sarcolemma and contraction begins when calcium is released from sarcoplasmic reticulum.

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