Autonomic Nervous System (ANS)

After reading this article you will learn about the anatomy and physiology of Autonomic Nervous System (ANS).

Various body activities are controlled by the nervous system. This is achieved by controlling the contraction of skeletal muscles throughout the body, contraction of smooth muscles in the organs, and secretion of both exocrine and endocrine glands in many parts of the body.

The motor axis of the nervous system (somatic) is responsible for controlling skeletal muscle contraction. Operating parallel to this axis is another similar system for control of the smooth muscles and glands called the ‘autonomic nervous system’.

The autonomic nervous system is also termed as the visceral, involuntary or veg­etative nervous system. It supplies nerves to the heart, blood vessels, glands, other visceral organs and smooth muscles and thereby maintains heart rate, blood pressure, respiration, gastrointestinal motility, urinary output and all other visceral functions within physiological limits.

So, it can also be said that the portion of the nervous system that controls the visceral functions of the body is called the ‘autonomic nervous system’. Autonomic Nervous system is that part of the nervous system that works independently to our conscious and voluntary control and enjoys some degree of autonomy.

Though the most important components of the ANS, in relation to clinical phar­macology, are the outflow (efferent) nerve tracts. It is becoming increasingly recog­nised that afferent nerves (particularly the non-myelinated nerves mediating visceral pain and other functions like cardiovascular, respiratory and other visceral reflexes) also have important effector functions in the periphery, mediated mainly by neuropeptides.

There is no exclusively autonomic area in the CNS; somatic and auto­nomic nerves are intermixing and integrated with each other. Posterior and lateral nuclei of hypothalamus are primarily sympathetic while anterior and medial nuclei are primarily parasympathetic.

The autonomic nervous system is activated mainly by centres located in the spinal cord, brain stem, and hypothalamus. Some portions of the cerebral cortex and specially of the limbic system can transmit impulses to the lower centres and thereby influence autonomic control.

Sensory signals from peripheral organs enter the centers of the autonomic ganglia, spinal cord, brain stem or hypothalamus and those in turn transmit appropriate reflex responses back to the visceral organs to control their activities.