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.

 B. The release of calcium ions causes myosin and actin to attach to each other. This statement best describes a cause and it's effects that occur during the process of muscle contraction.

Muscle contraction can be explained by sliding filament theory.  

1. Activation of muscles: the motor nerve generates an impulse to transfer signals from neurons to neuromuscular junction. This stimulates sarcoplasmic reticulum to release calcium into the muscle cells.

2.Contraction of muscles:  calcium in the muscle cells binds with troponin causes actin and myosin to bind. Actin and myosin in the muscle binds and contract by utilizing ATP as a source of energy.