Histology of Cardiac Muscles

Cardiac muscles, also called heart muscles or myocardium are one of the three types of muscle tissues, the other two being smooth and skeletal muscles. It is an involuntary muscle that comprises the main tissue of the heart wall. This article describes the histology (tissues and cells as seen under a microscope) of the cardiac muscles.

Histological Properties

• The cardiac muscle is a striated muscle that has actin and myosin filaments arranged in repeated units called sarcomeres. Sarcomeres are the smallest and functional units of the cardiac muscles.
• The cardiac muscles are similar to skeletal muscles in their striations but they are shorter in length.
• The cells of the cardiac muscles have a single nucleus that is centrally located.
• The cells also contain a large number of mitochondria since cardiac muscles require a large amount of energy in the form of ATP.
• The cardiac muscle fibre cells are profusely branched and are connected with each other by intercalated discs at their ends. The intercalated discs are present perpendicularly to the cardiac muscle fibres.
• The cell membrane of the cardiac muscle cells is called sarcolemma. The intercalated discs form a part of the sarcolemma.
• The intercalated discs contain other structures namely: adherens junctions, gap junctions and desmosomes.
• Gap junctions allow easy movement of the action potential and coordinate the contraction of the heart by forming channels between adjacent cardiac muscle cells.
• Desmosomes help in anchoring the ends of cardiac muscle fibres together, so that they do not pull out during rapid contraction.
• Endomysium is a sheath found above sarcolemma made of areolar connective tissues. It contains capillaries and nerves that meet the high oxygen demand of the cardiac muscles.

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