Question

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

Explanation:

In muscle contraction, calcium ions are released from the sarcoplasmic reticulum. When calcium ions are present, they bind to troponin - a protein associated with actin filaments. This binding causes a conformational change in troponin, which exposes the binding sites on actin for myosin. Then, myosin heads can bind to actin, forming cross - bridges and leading to muscle contraction.

Answer:

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