18. The Heart

Describe the pericardium and distinguish between the fibrous and the serous pericardia relative to histological structure and location.

Why is autonomic tone a significant part of ANS function?

The role of the atrioventricular node (AV node) is to __________.

Choose the correct sequence of electrical current flow through the heart wall.

The __________ nerve carries parasympathetic fibers to the sinoatrial (SA) node.

a. Name the elements of the intrinsic conduction system of the heart in order, beginning with the pacemaker.b. What is the important function of this conduction system?

The activity of the heart depends on intrinsic properties of cardiac muscle and on neural factors. Thus,a. vagus nerve stimulation of the heart reduces heart rate,b. sympathetic nerve stimulation of the heart decreases time available for ventricular filling,c. sympathetic stimulation of the heart increases its force of contraction,d. all of the above.

The cells of the conducting system differ from the contractile cells of the heart in that (a) conducting cells are larger and contain more myofibrils, (b) contractile cells exhibit pacemaker potentials, (c) contractile cells do not normally exhibit autorhythmicity, (d) both a and b are correct.

The autonomic centers for cardiac function are located in (a) the myocardial tissue of the heart, (b) the cardiac centers of the medulla oblongata, (c) the cerebral cortex, (d) all of these structures.

Trace the normal pathway of an electrical impulse through the conducting system of the heart.

What effect does sympathetic stimulation have on the heart? What effect does parasympathetic stimulation have on the heart?

What role do the chordae tendineae and papillary muscles play in the normal function of the AV valves?

If the papillary muscles fail to contract, (a) the ventricles will not pump blood, (b) the atria will not pump blood, (c) the semilunar valves will not open, (d) the AV valves will not close properly, (e) none of these happen.

The refractory period of cardiac muscle is much longer than that of skeletal muscle. Why is this a desirable functional property?