In Cardiac Muscle

Question

In cardiac muscle,
A) calcium ions are not released from the sarcoplasmic reticulum.
B) calcium ions do not bind to troponin molecules.
C) calcium ions play no role in the process of contraction.
D) about 20 percent of the calcium ion required for contraction comes from outside the cell.
E) calcium ions play an important role in repolarizing the membrane after the depolarization phase.

Accepted Answer

In cardiac muscle, about 20 percent of the calcium ion required for contraction comes from outside the cell. Calcium ions are also released from the sarcoplasmic reticulum and bind to troponin molecules to initiate the process of contraction. Calcium ions do not play a direct role in repolarizing the membrane, but rather in the depolarization phase.