Select the correct statement about the function of myocardial cells.
A) The refractory period in skeletal muscle is much longer than that in cardiac muscle.
B) Cardiac muscle cells are innervated by sympathetic, parasympathetic, and somatic nerve fibers so that the nervous system can increase heart rate.
C) The entire heart contracts as a unit or it does not contract at all.
D) The influx of potassium ions from extracellular sources is the initiating event in cardiac muscle contraction.

Question

Quizplus · Accepted Answer

Myocardial cells contract as a functional syncytium, meaning that the entire heart contracts as a unit, or it does not contract at all. This is different from skeletal muscle where individual muscle fibers contract independently of each other. Statement A is incorrect because the refractory period in cardiac muscle is much longer than that in skeletal muscle. Statement B is incorrect because cardiac muscle cells are mainly innervated by the autonomic nervous system and not somatic nerves, and the parasympathetic nervous system decreases heart rate rather than increasing it. Statement D is incorrect because the influx of calcium ions from extracellular sources, not potassium ions, is the initiating event in cardiac muscle contraction.

Select the Correct Statement About the Function of Myocardial Cells