How does the heart muscle contract?
Muscle contraction occurs due to the sliding in of actin and myosin myofilaments so that the length of the sarcomere decreases. Sarcomere is a segment of the muscle fibre and the muscle fibre contains several sarcomeres in series. All these units contract together to produce shortening of the muscle fibre in cardiac systole. Contraction occurs in response to an impulse conducted down the conduction system. The process of coupling the exciting stimulus to the contraction is known as excitation contraction coupling. Excitation contraction coupling is mediated by release of calcium from the sarcolemma, the membrane of the muscle fibre. Re-uptake of the calcium released by each cardiac cycle is done by the sarcoplasmic reticulum.