Distinguish between twitch summation and motor recruitment in a skeletal muscle
What will be an ideal response?
Twitch summation occurs when a muscle cell is repeatedly stimulated in rapid succession. All of the Ca2+ ions released during the first stimulation do not have time to be pumped back into the sarcoplasmic reticulum before more Ca2+ are released in response to a subsequent stimulation. Therefore, repeated rapid stimulation causes more Ca2+ availability to free up more binding sites on actin. The result is that the effects of subsequent twitches are summed, resulting in a stronger contraction, known as twitch summation. A motor unit is a single neuron and all the muscle cells innervated by that neuron. A single muscle has numerous motor units. When needed, the brain can stimulate (recruit) more motor units resulting in a stronger contraction; this is called motor unit recruitment.
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