Sypmathetic Nervous System

Sympathetic nervous system is a part of the autonomic nervous system of body. It is mainly concerned with mobilization of body’s resources under stress to induce the “fight or flight response“.

Sympathetic nervous system is also known as thoracolumbar outflow because it arises from T1 to L2 segments of the spinal cord.

The myelinated preganglionic fibers (white rami communicantes) arise from the lateral column of the spinal cord, emerge through the ventral rami where the white rami are connected to the ganglia of the sympathetic chain.

Preganglionic fibers relay either in the lateral ganglia (sympathetic chain) or in the collateral ganglia, e.g. the celiac ganglion. The non-myelinated postganglionic fibers (grey rami communicantes) run for some distance before reaching the organ of supply. The adrenal medulla is a unique exception in the body; it is supplied by the preganglionic fibers.

Sympathetic nerve endings are adrenergic in nature, meaning thereby that noradrenalin is produced for neurotransmission. The only exception to this general rule is the case of cholinergic sympathetic nerves supplying the sweat glands and skeletal muscle vessels for vasodilatation.

Functionally, sympathetic nerves are vasomotor (vasocons┬Čtrictor), sudomotor (secretomotor to sweat glands), and pilomotor (contract the arrector pili and cause erection of hair) in the skin of limbs and body wall. In addition, sympathetic activity causes dilation of pupil, pale face, dry mouth, tachycardia, rise in blood pressure, inhibition of hollow viscera, and closure of the perineal sphincters.

The blood supply to the skeletal muscles, heart and brain is markedly increased. Thus, sympathetic reactions tend to be ‘mass reactions’, widely diffused in their effect and that they are directed towards mobilization of the resources of the body for expenditure of energy in dealing with the emergencies or emotional crises (fright, fight, flight).