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Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart .
Typically, cardiomyocytes have a single, central nucleus, but can also have two or more. [1] Cardiac muscle cells branch freely and are connected by junctions known as intercalated discs which help the synchronized contraction of the muscle. [4] The sarcolemma (membrane) from adjacent cells bind together at the intercalated discs.
An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a muscle twitch. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from tetanus. Also, a loss of function at the junction can produce paralysis. [5]
Agonist muscles and antagonist muscles are muscles that cause or inhibit a movement. [5] Agonist muscles are also called prime movers since they produce most of the force, and control of an action. [6] Agonists cause a movement to occur through their own activation. [7]
The cardiac muscle cells, (also called cardiomyocytes or myocardiocytes), predominantly contain only one nucleus, although populations with two to four nuclei do exist. [ 16 ] [ 17 ] [ page needed ] The myocardium is the muscle tissue of the heart and forms a thick middle layer between the outer epicardium layer and the inner endocardium layer.
The papillary muscles extend from the walls of the heart to valves by cartilaginous connections called chordae tendinae. These muscles prevent the valves from falling too far back when they close. [24] During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and the tension on the chordae tendineae is slight.
A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. [1] In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). [2]
Gap junctions connect the cytoplasms of neighboring cells electrically allowing cardiac action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization of the heart muscle. [3] [2] All of these junctions work together as a single unit called the area composita. [2]