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Physical
Cardiac Muscle
Cardiac muscle is the involuntary, striated muscle that makes up the main tissue of the heart wall.
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The idea
Cardiac muscle, also called heart muscle or myocardium, is one of the three types of muscle tissue in vertebrates, along with skeletal and smooth muscle. It is involuntary, so it works without you thinking about it, and it is striated, or striped, like skeletal muscle. It forms the thick middle layer of the heart wall, between an outer layer and an inner layer.
Heart muscle cells are joined end to end by intercalated discs, forming long fibers. Inside each cell, fibers of actin and myosin slide past each other to make it contract. Special pacemaker cells set the rhythm of the heartbeat by sending out electrical impulses on their own. Each impulse causes calcium to be released inside the muscle cells, which triggers the contraction. The cells must contract together, and if that teamwork breaks down, as in ventricular fibrillation, the heart may not pump at all.
Pumping uses a lot of energy, so heart muscle needs a constant flow of blood, which the coronary arteries bring. Its cells are packed with mitochondria, which makes them highly resistant to tiring. When its blood supply is cut off, the muscle can be damaged, as in a heart attack.
Check yourself
Question 1 of 2
What joins heart muscle cells end to end into long fibers?
Composition
what it's made of
- Cardiomyocytes — The contracting heart muscle cells that let the heart pump.
- Intercalated Discs — Junctions that join the cells end to end into long fibers.
- Pacemaker Cells — Cells in the sinoatrial node and other spots that set the rhythm of the heartbeat.
- Mitochondria — Energy-producing parts of the cell that keep heart muscle from tiring.
- Coronary Blood Supply — Arteries on the surface of the heart that bring oxygen and nutrients to the muscle.
Connection
how it relates
Under Muscular System
Change
how and why it evolves
- Past
- Heart muscle forms and starts beating long before birth, early in an embryo's development.
- Now
- Today diseases of the heart muscle, called cardiomyopathies, are of major importance in medicine.
- Next
- Because adult heart muscle repairs itself only very slowly, researchers are testing ways to regrow damaged tissue, though these are still experimental.