Name the two distinct functional units myocardium present in

Name the two distinct functional units (myocardium) present in the heart. (2) What prevents action potentials from directly spreading from one cardiac myocardium to the other? (2) How then are electrical impulses conducted from one syncytium to the other? (2)

Solution

The two distinct functional units of myocardium are the cardiomyocytes and the cardiac pacemaker cells.

The action potential in cardiac cells is different from the other cells in the heart it arises from specialised group of cells that have automatic action potential generating capacity in normal heart the cells are found in right Atrium and are called sinoatrial node they have the capability of producing 60-100 action potentials per minute . This pass along the cell membrane causing the cell to contract 60-100 beats per minute. All the cardiac muscle cells are electrically linked to one another by gap junctions which allow action potential to pass from one cell to another.

The electrical conduction system in the heart transmit signals which result in contraction of the heart muscle the signal generated in sinoatrial node Travels through the right Atrium to the atrioventricular node and through bundle branches resulting in contraction this is signal stimulates contraction in right and left Atrium and then the ventricles this process helps to pump blood flow of the body.

Myocardial cells have negative membrane potential when at rest, when there is stimulation above threshold value the Ion channels open and cations enter the cell the positive charged ions cause depolarization characteristics of action potential, this causes the opening of voltage gated calcium channels and Calcium is released from the t-tubules. Th is influx of calcium causes muscle contraction ,after sometime potassium channels reopen causing outflow of potassium resulting in repolarization to resting state.