Chapter 14, Problem 1CP

Summary Introduction

To review:

Effects of sympathoadrenal and parasympathetic nerve activities on the cardiac rate and stroke volume.

Introduction:

Sympathoaderanal is the connection between the sympathetic nervous system and adrenal medulla. Sympathetic nervous system affects various regions of the heart. Parasympathetic nerve system is a part of the autonomic nervous system which slows down the heart rate by conserving energy.

Explanation of Solution

Sympathoadrenal system stimulates the cyclic AMP (adenosine monophosphate) production. Norepinephrine secreted from the sympathetic axons and epinephrine released from the adrenal medulla attach to the β1 adrenergic receptors. The action of cyclic AMP, on the calcium channels located on the pacemaker cells, results in the production of a pacemaker potential which, in turn, raises the rate of diastolic depolarization. This results in a faster cardiac rate. The effects of sympathoadrenal system include elevated conduction rate in the AV (atrio-ventricular) node, and the strength of both atrial and ventricular muscle contractions increases.

Norepinephrine and epinephrine increase contraction in the fibers which cause the amount of blood being released to increase. Hence, the stroke volume also rises. Parasympathetic nerve releases acetylcholine (Ach) which reduces the rate of diastolic depolarization by binding to the Ach receptors and causes diffusion of potassium outside. The cardiac rate also declines. Conduction rate decreases in the AV node, and the stroke volume also declines.