Overview of the autonomic nervous system (ANS)

The autonomic nervous system is the visceral motor system. It regulates the contraction of smooth muscle and heart muscle and control glandular secretion therefore key physiological variables (example, cardiac output, blood pressure, core temperature, blood glucose) are maintained at levels suitable to the environment or ongoing activities. The word autonomic is apt as the ANS generally operates without conscious awareness and has no cognitive component. However by definition there are no afferents in the ANS its reflex activities are controlled by visceral afferent and somatic input.
The ANS is anxious with feedback regulation of physiological variables. For illustration, mean arterial blood pressure is reserved fairly steady in the face of changes in posture. On rapidly standing from a lying position the gravitational pooling of blood in the legs is offset by autonomic reflexes that elicit vasoconstriction of leg blood vessels. This sustains blood pressure by negative feedback.

Most of the autonomic adjustments, however not negative feedback, are homeostatic in that they change physiological variables therefore as to cope with modified demands. In response to a broad range of stressors, establishment of the sympathetic nervous system (SNS) to targets like the blood vessels, heart, airways, and liver outcomes in increased cardiac output, regional alterations in blood flow, increased airflow through the lungs, and rises in blood glucose concentrations, all adaptations that improve the chances of surviving the stress unscathed. In common the SNS mediates the response of “fright, fight, and flight.” Contrary, parasympathetic nervous system (PNS) activation is seen whenever the body is in “rest and digest” mode; the PNS usually stimulates exocrine gland secretion and promotes anabolic procedures.

The sympathetic and parasympathetic divisions of the ANS frequently have opposing effects on a system, for illustration on pupil diameter or heart rate, and it is the equilibrium of activities in the two distributions which achieves the suitable outcome. In some circumstances the ANS works by positive feedback. The sexual responses in humans need autonomic reflexes (both sympathetic and parasympathetic) in which the motor response increases the firing of similar visceral afferents that drive the reflex response. This is positive feedback as it carries the system away from its normal stable state.