Action potentials traveling down the plasma membrane of a muscle fiber will next reach the
A) plasma membrane.
B) sarcoplasmic reticulum.
C) cytoskeletal system.
D) T tubules.
E) endomembrane system.

Question

Quizplus · Accepted Answer

Action potentials traveling down the plasma membrane of a muscle fiber will next reach the T tubules. T tubules are invaginations of the plasma membrane that penetrate deep into the muscle fiber, allowing the action potential to spread from the surface of the cell to the interior, where it activates the release of calcium ions from the sarcoplasmic reticulum.

Action Potentials Traveling Down the Plasma Membrane of a Muscle