PRACTICE QUESTIONS

1. An increase in heart rate could result from:

a. An increase in sympathetic nerve activity to the heart

b. An abnormally rapid decrease in permeability of SA node cells to K' during diastole

c.

d. A decrease in parasympathetic nerve activity to the heart

e. All the above

2. In which of the following arrhythmias will there be more atrial beats per minute than ventricular beats?

a. Complete (third-degree) AV block

b. Frequent premature ventricular contractions

c. Sick sinus syndrome (sinus bradycardia)

d. First-degree AV block

e. Ventricular tachycardia

3. 'Fhe normal pathway followed by a cardiac action potential is to begin in the SA node and then pro­pagate:

a. Across the atria in the bundle of His

b. Through the connective tissue layers that separate the atria and ventricles

c. Across the atria and to the AV node

d. From the left atrium to the right atrium

e. From the left atrium to the left ventricle and from the right atrium to the right ventricle

4. Which statement is true⁷.

a. The refractory period of cardiac muscle cells is much shorter than their mechanical contraction.

b. The cardiac action potential propagates from one cardiac cell to another through nexi, or gap junc­tions.

c. Purkinje fibers are special nerves that spread the cardiac action potential rapidly through the ventricles.

d. Ventricular muscle cells characteristically depolarize spontaneously to threshold.

e. The permeability of ventricular muscle cells to Ca²⁺ is lower during the plateau of an action potential than it is at rest.

5. Which of the following types of drugs would be the best choice to treat a patient with both supraventricular tachy­cardia and inadequate cardiac contractility?

a.

b. Muscarinic cholinergic antagonist

c. Beta-adrenergic agonist

d. Cardiac glycoside (inhibits Na*,K* pump)

e. Calcium channel blocker

6. During which phase of a normal ventricular action poten­tial is it most likely that fast Na⁴ channels are in an inactivated state» slow Ca²⁺ channels are open, and most K⁴ channels are closed?

a. Phase 0 (rapid depolarization)

b. Phase 1 (partial repolarization)

c. Phase 2 (plateau)

d. Phase 3 (repolarization)

e. Phase 4 (rest)

7. Wliich of the following is true for both cardiac muscle and skeletal muscle?

a. The muscle forms a functional syncytium.

b. An action potential in the muscle cell membrane is required to initiate contraction.

c. Pacemaker cells spontaneously depolarize to thresh­old and initiate action potentials.

d. Frequent action potentials in motor neurons can cause a sustained (tetanic) muscle contraction.

e. Extracellular Ca²* that enters the muscle cell during an action potential triggers the release of additional Ca²⁺ from the sarcoplasmic reticulum.