18. The Heart

How would you expect the absolute refractory period of a contractile cell to change if more potassium channels opened sooner after polarization?

The movement of ions in opposite directions at the same time is responsible for which of the following?

Which statement below correctly describes how the channels that are active during the pacemaker potential are different from other ion channels used in action potentials?

More than one choice may apply.

Which of the following depolarizes next after the AV node?

The cardiac skeleton of the heart has which two of the following functions?

(a) It physically isolates the muscle fibers of the atria from those of the ventricles.

(b) It maintains the normal shape of the heart.

(c) It helps distribute the forces of cardiac contraction.

(d) It allows more rapid contraction of the ventricles.

(e) It strengthens and helps prevent overexpansion of the heart.

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

What is the cardiac cycle? What phases and events are necessary to complete a cardiac cycle?

Which of the following is longer?

(a) The refractory period of a cardiac contractile cell.

(b) The refractory period of skeletal muscle fiber.

Describe the function of the SA node in the cardiac cycle. How does this function differ from that of the AV node?

What are the sources and significance of the four heart sounds?

Describe the effects of epinephrine, norepinephrine, glucagon, and thyroid hormones on the contractility of the heart.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The rapid depolarization phase of the contractile cell action potential is due to the opening of voltage-gated potassium ion channels.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Pacemaker cells lack a distinct plateau phase.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The plateau phase in contractile cells is due to the influx of calcium ions through calcium ion channels.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The repolarization phase of the contractile cell is due to the potassium ions rushing into the cell through potassium ion channels.