Cardiac muscles are the kinds of muscles that are in the heart. Self-contracting, these striated muscles, which are similar to skeletal muscles in this manner, are highly resistant to fatigue. They contain a large number of mitochondria, which enable continuous aerobic respiration and a good blood supply that provides nutrients and oxygen for the various functions of the body. As the cardiac muscles contract, they propel blood into the heart and through the blood vessels of the circulatory system.
Cardiac muscles, which are comprised of Y-shaped cells, are like smooth muscles because they have nuclei that are centrally located and many cells are required to span the length of the muscle. However, cardiac muscles differ from both the skeletal and smooth muscles in that they are joined to each other not by tendons or ligaments but rather intercalated disks. An intercalated disc is a gyrating double membrane that separates adjacent cells in the cardiac muscle fibers. They support synchronized contraction of cardiac tissue and can easily be visualized longitudinally.
There are three types of membrane junctions that existed within the intercalated disc. These are known as the:
- Fascia adherens
- Macula adherens
- And gap junctions.
An important feature of cardiac muscles is their ability to contract rhythmically at a steady rate. For example, if two cardiac muscle cells are in contact with each other, the one that contracts first will stimulate the other to contact and so forth and so on. This ability to contract rhythmically is regulated by the autonomic nervous system. In addition, special pacemaker cells, located at the entrance of the right atrium, an area which is commonly called the sinoatrial node, generate impulse signals. Although these cells don’t generally contract – they do have the ability, but it is not their primary function – they stimulate other cells in the heart to do so.
During a heart attack, for example, the pacemaker cells may not function properly. This can cause terrible difficulties for an individual, including (but not limited to) death.