THE INVOLUNTARY NERVOUS SYSTEM

This second part controls the internal organs – heart, blood-vessels, lungs, intestines, etc., even the flow of saliva and sweat. It has its headquarters in a brain centre connected with a delicate network of fibres lying on either side of the spinal column (backbone), from which numerous threadlike branches pass to the internal organs. This second part is not under our immediate control but – and this is of paramount importance in understanding ‘nerves’ – it responds to our moods. For example, when we are afraid our cheeks blanch, our pupils dilate, our heart beats quickly and our hands may sweat. We do not consciously react like this and we have no power to stop these reactions other than to change our mood. We therefore call this part of the Involuntary Nervous System.

The involuntary nervous system itself consists of two parts, the sympathetic and the parasympathetic. Of these, the sympathetic ‘sympathizes’ more demonstratively with our moods, hence its name. The action of the sympathetic nerves strengthens an animal’s defences against the various dangers which beset it, such as extremes of temperature, deprivation of water, attack by its enemies.

Have you ever seen a frightened animal standing stock-still from fear before taking flight? Its nostrils and its pupils dilate, its heart races, it breathes quickly. The sympathetic division of the involuntary nervous system has prepared it for fight or flight.