ABSTRACT

The autonomic nervous system (ANS) adjusts the contraction of smooth muscle and heart muscle and controls glandular secretion so that key physiological variables are maintained at levels appropriate to an animals' activity or the environment in which it finds itself. The classical view of the ANS is that it is exclusively a visceral motor system, the activities of which can be altered by sensory input. To a first approximation much of the activity of the ANS is concerned with homeostatic regulation of physiological variables. Many autonomic adjustments are not negative feedback, since they do not defend a set point in some variable, but are homeostatic in that they change physiological variables so as to cope with altered demands. Sexual responses in humans require autonomic reflexes in which the motor response increases the firing of the same visceral afferents which drive the reflex response. Hence transmission between interneuron and motor neuron is fast.