Question

Which of the following statements about the action potentials in contractile myocardial cells (cardiac muscle) is INCORRECT? Compared to skeletal muscle cells, contractile myocardial cells have a lower (more negative) resting membrane potential. Action potentials are propagated between adjacent cardiomyocytes through gap junctions. The duration of an action potential in a contractile myocardial cell is greater than the duration of an action potential in a typical neuron. During the repolarization phase of a contractile myocardial action potential, the cell is highly permeable to sodium, potassium and calcium.

Answer 1

Answer: During the repolarization phase of a contractile myocardial action potential, the cell is highly permeable to sodium, potassium and calcium.

Explanation:

Apart from the fact that contractile cells conduct impulses, it also helps in contractions which are needed for pumping of blood. It should also be noted that the myocardial conducting cells serves as the heart's conduction system. They also have a lower resting membrane potential.

Of the options given, the answer is the last option i.e. during the repolarization phase of a contractile myocardial action potential, the cell is highly permeable to sodium, potassium and calcium. This is wrong.

Repolarization occurs due to a rise in the permeability of potassium and during repolarization, the calcium channels close.