Final answer:
Calcium-induced calcium release (CICR) is the process where the increase of Ca2+ in the cytoplasm opens Ca2+ release channels in the sarcoplasmic reticulum, leading to muscle contraction.
Step-by-step explanation:
The phenomenon where Ca2+ release channels in the sarcoplasmic reticulum (SR) of the heart are opened by an increase in Ca2+ in the cytoplasm is referred to as Calcium-induced calcium release (CICR). This process is pivotal in the physiology of cardiac and skeletal muscle. An action potential traveling down the T-tubules triggers the release of Ca2+ from the SR into the sarcoplasm, promoting muscle contraction.
Propagation of an action potential along the sarcolemma and into the T-tubules allows for the opening of calcium channels in the SR membrane, leading to the diffusion of Ca2+ into the sarcoplasm. This influx of Ca2+ is crucial for the muscle fiber to initiate contraction by its contractile units or sarcomeres. As long as Ca2+ ions remain bound to troponin and ATP is present, muscle contraction can continue.