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Summary of Drug Acting on ANS :-

The autonomic nervous system is a coordinated motor system that consists of innervated cardiac muscle, smooth muscle, and glands. The ANS maintains homeostasis and provides a coordinated response to external stimulation. Much of homeostasis occurs involuntarily, but some autonomic processes have a degree of voluntary control (urination, sexual activity). The major components are the sympathetic and parasympathetic nervous systems. This review will focus on those aspects of the autonomic nervous system that are most crucial in the clinical assessment and treatment of disease. Many elements of the ANS, thermoregulation and the emotional component to sympathetic stimulation, for example, will be omitted.

Autonomic nervous system (A.N.S.) is a peripheral complex of nerves, plexuses and ganglia that are organized to modulate the involuntary activity of the secretory glands, smooth muscles and visceral organs. This system functions to sustain homeostatic conditions during periods of reduced physical and emotional activity, and equally important, to assist in internal bodily reactions to stressful circumstances.

Nerves transmit their impulses across most synapses and neuroeffector junctions by means of specific chemicals called as neurophumoral transmitters or simply neurotransmitters.

The autonomic drugs exert their actions on smooth muscles, cardiac muscles, glands and visceral organs by mimicking or modifying the action of neurotransmitters released by autonomic fibers either at ganglia or at effector cells.

GENERAL FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM :-
The integrating action of the autonomic nervous system is of vital importance for the well being of the organism. In general, the autonomic nervous system regulates the activities of the structures that are not under voluntary control and that function below the level of consciousness. Thus, respiration, circulation, digestion, body temperature, metabolism, sweating and the secretions of certain endocrine glands are regulated, in part or entirely, by the autonomic nervous system. The constancy of internal environment of the organism is to a large extent controlled by the vegetative or autonomic nervous system.

The sympathetic system and its associated adrenal medulla are not essential to life in a controlled environment. Under circumstances of stress, however, the lack of sympathoadrenal functions becomes evident. Body temperature can not be regulated when environmental temperature varies; the concentration of glucose in blood does not rise in response to urgent need; compensatory vascular response to hemorrhage, oxygen deprivation, excitement and exercise are lacking; resistance to fatigue is lessened; sympathetic components of instinctive reactions to the external environment are lost; and other serious deficiencies in the protective forces of the body are discernible.

The sympathetic system normally is continuously active; the degree of activity varies from moment to moment and from organ to organ. In this manner, adjustments to a constantly changing environment are accomplished. The sympathoadrenal system also can discharge as a unit. This occurs particularly during rage and fright, when sympathetically innervated structures over the entire body are affected simultaneously.