Question

multiple choice question
the heartbeat is initiated by the specialized cardiac muscle cells of the ____ which are located in the posterior wall of the right atrium, adjacent to the entrance of the ____.

o internodal tracts; coronary sinus
o atrioventricular node; inferior vena cava
o epicardium; sinus venosus
o sinoatrial node; superior vena cava

Explanation:

The sinoatrial (SA) node, often called the natural pacemaker of the heart, initiates the heartbeat. It is located in the posterior wall of the right atrium, adjacent to the entrance of the superior vena cava. The other options do not correctly identify the structure that initiates the heartbeat and its location.

Answer:

D. sinoatrial node; superior vena cava