Autonomic Nervous System

The autonomic nervous system is the part of the central and peripheral nervous systems which regulates the activity of structures not normally under voluntary control. It is also referred to as 'the vegetative nervous system'. It provides the motor innervations of smooth muscle, cardiac muscle and gland cells. The system consists of two physiologically and anatomically distinct parts or divisions producing opposite action. The word 'autonomic' means 'being functionally independent'.

Professor Svetoslav Danev describes the autonomic nervous system and its two complementary components as follows:

". . . the complex series of neural connections, linking all organs to the brain to control the whole internal environment. It is the body's major defense against physical stress (such as heat, cold or exercise) and psychological stress, and the system that demonstrates the principal symptomatic manifestation of stress in its early stages."

The functions of the two parts of the autonomic nervous system, which counterbalance each other, can be summarized as thus:

* Sympathetic Nervous System - activates organs, preparing to cope with exercise or other physical or psychological stress. Activation of the sympathetic nervous system is associated with the 'fight or flight' response and causes a range of physiological effects such as increased heart rate and breathing.

* Parasympathetic Nervous System - controls background functions in the body and is responsible for 'repair and recovery'. This system controls internal organs at times of relaxation when, for example, the subject is resting or sleeping. Parasympathetic control of beating of the heart is medicated via the vagus nerve, the level of nerve impulse traffic often being referred to as 'vagal tone'. Increased parasympathetic activity thus corresponds to increased cardiac vagal tone.