18. The Heart

Which of the following correctly identifies a difference between action potentials in cardiac and skeletal muscle?

Calcium ion channels open in response to changes in membrane potential. What type of opening mechanism do calcium ion channels in cardiac muscle exhibit?

Autorhythmicity is a unique feature of cardiac pacemaker cells. What feature of cardiac pacemaker cells allows them to be autorhythmic while other cardiac cells are not?

Cardiac contractile tissue uses sodium, calcium, and potassium channels for depolarization and repolarization. During which phase of the action potential is the calcium channel open?

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?

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

a. 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.

b. 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.

c. 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.

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

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

e. Open sodium ion channels cause hyperpolarization in pacemaker cells, which triggers HCN channels to open and begins a new action potential.

What are the effects of the plateau phase of the contractile cell action potential?

Explain what each of the following terms represents on an electrocardiogram (ECG).

a. P wave

b. QRS complex

c. T wave

d. P-R interval

e. S-T segment

An experimental toxin makes the refractory period of cardiac muscle cells equal in length to that of skeletal muscle fibers. Predict the consequences of this toxin. (Connects to Chapter 10)