NEURAL CONTROL OF CARDIAC-FUNCTION

The principal functions of the heart are regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system. In gene ral, the sympathetic nerves to the heart are facilitatory, whereas the parasympathetic (vagus) nerves are inhibitory, The kinetics of the tw o autonomic divisions differ substantially. The vagal effects develop very rapidly, often within one heartbeat, and they decay quickly as we ll. Hence, the vagus nerves can exert beat-by-beat control of cardiac function. Conversely, the onset and decay of the sympathetic effects a re much more gradual; only small changes are effected within the time of one cardiac cycle. When both autonomic systems act concomitantly, t he effects are not additive algebraically, but complex interactions pr evail. Such interactions may be mediated either pre-junctionally or po st-junctionally with respect to the neuro-effector junction.