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?

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.