"Parasympathetic nerves leave the central nervous system...

"Parasympathetic nerves leave the central nervous system from the upper regions where they travel in cranial nerves (i.e., 12 pairs of nerves attached to the brain and serving head and neck), and from the lowermost regions of the spinal cord where they travel in spinal nerves. "Most internal organs of your body are supplied with both parasympathetic and sympathetic nerve fibres." "In general, these two types of nerves work in opposite ways.

For example, impulses travelling along sympathetic nerve fibres toward the heart increase your heart-beat rate, whereas impulses travelling along the parasympathetic nerves leading to the heart disease its rate. "When we examine the effects of sympathetic stimulation of various organs, a pattern begins to emerge.

We find that sympathetic stimulation causes a number of events: Widening of air passage leading to the lungs; Constriction or narrowing of blood vessel in the skin and in the intestinal tract, resulting in blood being shifted from the digestive organs and skin to the muscles; A general slowing down of movements in the intestinal tract; An increase in the force and rate of heart-beat: Release of the blood sugar from the liver; Release of the harmones adrenaline.

All of these activities prepare the human being for emergencies such as running or fighting. The widening of air passages makes it easier for the human being to beathe faster and get more oxygen. Blood is shifted from regions where it will not be needed during the emergency (the intestinal tract, for example) to skeletal and heart muscle which will need oxygen and blood sugar. The heart beats faster and stronger so that blood circulates through the muscles at a higher rate.

Blood sugar is released from storage in the liver into the blood stream where it will be available to supply muscles with energy. In short, sympathetic stimulation prepares the man for emergencies, and in this process, increases the blood pressure, retards the function of digestive system and increases the sugar contents of the blood.

The function of Parasympathetic nerves system is opposite to the sympathetic system "It widens the veins, releases noradrenalin hormones and generally retards activities. "The two nervous systems run parallel to each other and in co-operation from one part of the body to another.