The arrival of an action potential in a muscle fiber causes
A) calcium to enter the muscle fiber.
B) calcium to be released by internal organelles.
C) ACh to enter the muscle fiber.
D) ACh to be released by internal organelles.

Question

Quizplus · Accepted Answer

The arrival of an action potential in a muscle fiber causes calcium ions to be released from the sarcoplasmic reticulum, an internal organelle, into the cytosol of the muscle cell. This increase in calcium concentration initiates muscle contraction.

The Arrival of an Action Potential in a Muscle Fiber