Cardiac conducting myocytes (histology)

Certain myocytes within the myocardium are adapted for the generation and conduction of electrical impulses from atria to ventricles. Usually, they are morphologically distinct from the normal myocardial cell; however, both can pass the signal for contraction - the flow of ions through intercellular gap junctions - to neigbouring cells.

Cells of the cardiac conduction system are found in the:

• sinuatrial node
• internodal tracts
• atrioventricular node
• atrioventricular bundles
• Purkinje fibres
• the fibres that pass between these groups

Generally, the size of these cells is larger than contractile myocytes, but size decreases with distance from the sinuatrial node.

Relative to contractile cardiac myocytes, the conducting myocyte is noted for:

• fewer myofibrils; nevertheless, conducting cells have been observed to contract
• a greater volume of the cell occupied by cytoplasm
• more spherical and central nucleus
• more glycogen within the cell

In addition, the cells of the conduction system may show close association with nerve cells. This is the link to the autonomic nervous system that regulates the activity of the myocytes e.g. speed of conduction.