The cardiac electrical impulse normally begins spontaneously in the sinoatrial (SA) node because it:
A) has a superior location in the right atrium.
B) is the only area of the heart capable of spontaneous depolarization.
C) has rich sympathetic innervation via the vagus nerve.
D) depolarizes between -50 and -60 mV, rather than between -60 and-70 mV.

Question

Quizplus · Accepted Answer

The SA node depolarizes at a higher resting membrane potential (-50 to -60 mV) compared to other cardiac cells, allowing it to reach the threshold for depolarization more easily and initiate the cardiac impulse.

The Cardiac Electrical Impulse Normally Begins Spontaneously in the Sinoatrial