Question

In the heart, which of the following apply?
(1) Action potentials are conducted from cell to cell across the myocardium via gap junctions
(2) The SA node sets the pace for the heart as a whole
(3) Spontaneous depolarization of cardiac cells can occur in the absence of nerve stimulation
(4) Cardiac muscle can continue to contract for long periods in the absence of oxygen
a. All of the above
b. 1, 3, 4
c. 1, 2, 3
d. 2, 3

Accepted Answer

Step 1: Understand the role of gap junctions in the heart. Gap junctions allow direct electrical communication between cardiac muscle cells, enabling action potentials to spread rapidly across the myocardium. This supports statement (1). Step 2: Consider the function of the sinoatrial (SA) node. The SA node is known as the natural pacemaker of the heart because it initiates the electrical impulses that set the heart rate, supporting statement (2). Step 3: Evaluate the ability of cardiac cells to depolarize spontaneously. Cardiac muscle cells, especially those in the SA node, can generate action potentials without external nerve stimulation, which supports statement (3). Step 4: Analyze the effect of oxygen deprivation on cardiac muscle contraction. Unlike some muscle types, cardiac muscle cannot sustain contraction for long periods without oxygen because it relies heavily on aerobic metabolism, which means statement (4) is false. Step 5: Based on the evaluation of each statement, identify which combination of statements is correct by excluding the false one and selecting the appropriate answer choice.

Verified video answer for a similar problem:

Key Concepts

Gap Junctions and Action Potential Conduction in the Myocardium

Role of the SA Node as the Heart's Pacemaker

Spontaneous Depolarization and Oxygen Dependence of Cardiac Muscle