Sympathetic system is the larger subdivision of the autonomic system and includes two ganglionated cords with their branches, plexuses and includes two ganglia.
It has a much wider distribution as it innervates all the sweat gland of the skin, arrectores pilorum muscles, muscular walls of blood vessels in addition to viscera.
The preganglionic fibres of the thirteen thoracic and the first four lumbar segments of spinal cord are interrupted in the ganglia situated on either side of the vertebral column.
The ganglia form a ganglionated trunk on either side of the vertebral column extending from the head to the sacrum.
The number of ganglia correspond to the number of segments of the spinal cord in the thoracic, lumbar and sacral regions but in the cervical region (in the adult) there are generally only two ganglia superior and inferior and there is only one unpaired coccygeal ganglion.
The preganglionic fibres arising from the lateral horn cells of spinal cord pass via the ventral root of the spinal nerve and enter the ganglion of the sympathetic trunk and from here, postganglionic fibres supply the viscera. Some of the postganglionic fibres join back the spinal nerve and supply vasoconstrictor fibres to blood vessels, sudomotor fibres join sweat glands and the pilomotor fibres to arrectores pilorum muscles.
Thus the sympathetic ganglia are connected to the spinal nerve by a ramus communicans containing the preganglionic efferents from the spinal cord to the ganglia and afferents from viscera and by a gray ramus communicans containing postganglionic fibres from the ganglion which supply blood vessels, sweat glands and arrectores pilorum muscles.
In addition to the ganglionated sympathetic trunk, the coeliac, anterior mesenteric and posterior mesenteric ganglia represent the collateral ganglia in which sympathetic efferent are relayed.
These ganglia are present in the abdominal cavity on the walls of the corresponding arteries and the postganglionic fibres supply the viscera of the abdominal and pelvic cavities.
