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Cardiac Muscles

Cardiac Muscle is the involuntary striated muscle which is found in the histological foundation and walls of the heart, specifically in the myocardium. The cardiac muscle is one of the three major muscles types, the others are the smooth muscle and skeletal muscle. These muscles form in the process of myogenesis. The cells which constitute cardiac muscle are called myocardiocytes or cardiomyocytes which contain only three nuclei. The myocardium is the heart’s muscle tissue which forms a thick middle layer between the inner endocardium layer and the outer epicardium layer. The coordinated contractions of the cardiac muscle cells of the heart propel the blood out of the ventricles and atria to the blood vessels of the pulmonary and systemic circulatory systems. Through this complex mechanism, the systole of the heart is illustrated.

The cells of cardiac muscle rely on available electrical and blood supply in order to deliver nutrients and oxygen and it also helps to remove the waste products like carbon dioxide. The coronary arteries help to fulfill this. It is a relatively short, branched fiber which measure approximately 50 to 100 micrometers in length and 10 to 20 micrometers in diameter. Thin and thick myofilaments are organized and present in to the myofibrils. An alternating light and dark striations and bands are created due to their overlapping arrangement that looks similar to those seen in the skeletal muscle tissue. The myofibrils are surrounded by the sarcoplasmic reticulum tubules. However, they do not have terminal cisternae and are not well organized.

The mitochondria in the cardiac myocytes are numerous in numbers and large in size. They supply ATP which is needed for the repeated contractions of heart. Unlike other kinds of muscle tissues, the cardiac myocytes are joined end to end by the intercalated discs. These highly convoluted, complex couplings contain both electrical junctions and anchoring junctions. The desmosomes and fascia adherents forms the anchoring junctions that attach the adjacent myocytes. The electrical junctions are being composed of connexon protein channels that occur usually in clusters that are referred to as gap junctions. The connexon proteins span the distance between the adjacent plasma membranes and the ions travel through channel pores. The movement of ion allows the action potentials to pass directly from one cell to another. This makes the entire act like a single cell.

As the heart is mainly composed of cardiac muscle so it plays an important role for the functioning of the heart. The intercalated cells of this muscle help to contract multiple cells. The cells which cause it to contract are known as pacemaker cells. The cardiac muscle never gets tired although it works constantly by contracting and relaxing twice per second. It uses oxygen to generate adenosine triphosphate. The muscle cells also break down the glucose in to pyruvate. When there is a lack of oxygen supply and when the cardiac muscle has to work more, it uses up the glucose which is present in the bloodstream. It happens mostly when we exert ourselves. The cardiac muscle is not able to produce adenosine triphosphate when the level of oxygen becomes low.

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