The Autonomic nervous system

The autonomic nervous system supplies the internal organs and is so called because these organs function without conscious effort – that is, their functions are automatic, i.e. you can blink or move your finger at will, but you cannot voluntarily control your heart rate or how fast your stomach digests food.  The autonomic nervous system controls the involuntary movements of smooth and cardiac muscle, and of the glands, and is part of the peripheral nervous system.

The autonomic nervous system is connected to the blood vessels and the organs in the body by nerves.  It is controlled by the medulla oblongata and hypothalamus, which receive impulses from the central nervous system.

There are two parts to the autonomic nervous system, the sympathetic and parasympathetic nervous systems, which have opposite effects as these systems work antagonistically.  Each organ has a sympathetic and parasympathetic nerve supply.

The sympathetic nervous system has nerves that are responsible for actions in time of stress and are made of a network of interlaced nerves or plexuses.  The nerves supply internal organs and run back to the spinal nerves.  It also has nerves which supply the blood vessels, sweat and sebaceous glands and the arrector pili muscle in the dermis.

• The parasympathetic nervous system has branches which run to all the internal organs and control everyday bodily activities such as digestion and urination.  They are directed towards relaxation and restorative processes.  The heart rate slows, blood pressure drops and the digestive system becomes active.

In an emergency, such as when we feel threatened, the sympathetic nervous system has immediate effects on the body.  Sympathetic nerves stimulate the adrenal glands to produce the hormone adrenalin.  The hormone is distributed quickly by the blood and stimulates organs into greater activity. When the emergency is over the parasympathetic system returns the body to its normal state.

Example of how these systems work together in a stressful situation:

• The sympathetic impulses become stronger as a reaction to stress, the heart beats faster, blood vessels dilate, hairs stand on end.  The sweat glands produce more sweat and blood pressure rises due to the constriction of small arterioles in the skin.  Adrenaline is produced and the metabolic rate is increased.

• When the stressful situation passes the parasympathetic nerves take over and help the function of the organs return to normal and prepare the body for rest.