3which statement best describes a cause and its effect that occurs during the process of muscle contraction? a. the release of calcium ions causes myosin and actin to attach to each other. b. the pull of myosin on actin causes the motor neuron to send a nerve impulse. c. the presence of calcium ions within nerve cells causes the sarcomere to shorten. d. the shortening of the sarcomere causes the release of calcium around the myofibrils.

A. The release of calcium ions causes myosin and actin to attach to each other.

The contraction of skeletal muscles takes place by induction of a nerve impulse, which produces a movement and the interaction of the filaments containing proteins named as actin and myosin. This interaction of filaments is regulated by proteins  called tropomyosin and troponin present on the actin filaments. The motor nerve causes the depolarization of the muscle membrane sarcolemma. This triggers the sarcoplasmic reticulum to release calcium ions. This calcium binds to troponin and thus allows the tropomyosine strand on the actin filament to displace so that the part of the actin where myosine head needs to be attached remain uncovered. Binding of the actin myosine filament results in contraction.

Hence, the release of calcium ions causes myosin and actin to attach to each other causes muscle contraction.

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