Question

Which of the following is true about the autorhythmic cardiac cells?

	Their depolarization occurs due to the influx of calcium via leaky channels.
	They have stable resting potentials.
	Their action potentials have a plateau.
	They are found in only the walls of the atria.
	Their autorhythmicity can be modulated by the autonomic nervous system.

Answer 1

Answer:

Statement C; Their action potentials have a plateau

Statement E; Their auto rhythmicity can be modulated by the autonomic nervous system

Explanation: As against the other normal cells of the human body, the cardiac muscle fibers work throughout the life time of an individual without getting fatigued. Hence, on account of this they do not have a stable resting potential.

Similarly, during the spread of the cardiac impulses we get to see that there are present right and left Bundle of His present in the right and left ventricles of the heart respectively followed by the Purkinje fibers. Thus, since these two set of nodal tissues are present in the ventricular walls, it is not likely that the autorhythmic cardiac cells are only found in the atria of the heart.

Further, the cardiac muscles are set under action potential; that is their depolarization takes place. This is mainly due to the influx of the sodium ions. Further, the influx of the calcium ions do account for the depolarization event to happen; however their movement takes place through voltage gated channels and not the leaky channels.

Despite the fact, that the cardiac muscle fibers are self excitatory in nature, it is known that they can be modulated/altered by some hormones released due to the action of the autonomic nervous system; sympathetic and parasympathetic branch. While sympathetic nervous system increases the heart beat rate; the parasympathetic nervous system branch decreases it.

Also, a plateau stage is observed in the action potential of the auto rhythmic cardiac cells due to the continuous movements of the Na+, ca2+, and K+ ions.