During contraction of heart muscle cells ________.
A) all of the calcium required for contraction comes from storage in the sarcoplasmic reticulum
B) some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores
C) calcium is prevented from entering cardiac fibers that have been stimulated
D) the action potential is prevented from spreading from cell to cell by gap junctions

Question

Quizplus · Accepted Answer

During contraction of heart muscle cells, some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores, mostly from the sarcoplasmic reticulum. This process is known as calcium-induced calcium release and it amplifies and sustains the initial calcium signal, leading to muscle contraction. Calcium is not prevented from entering cardiac fibers that have been stimulated, and gap junctions allow the action potential to spread from cell to cell.

During Contraction of Heart Muscle Cells ________