THE SYMPATHETIC SYSTEM This system is made up of two gangliated cords running down one on each side of the vertebral column and ending below in the median coccygeal ganglion. In the neck the cords lie in front of the anterior tubercles of the transverse processes of the cervical vertebrae, in the thorax, in front of the heads of the ribs, while in the abdomen they lie in front of the sides of the bodies of the vertebrae. In addition to these cords there are numerous ganglia and plexuses through which the sympathetic nerves pass on their way to or from the viscera and blood-vessels.
A typical ganglion of the sympathetic chain is connected with its corresponding spinal nerve by two branches called rami corn municantes, one of which is grey and the other white (fig. 4). The white consists of medullated fibres belonging to the central nervous system, and these are splanchnic afferent or centripetal, and efferent or centrifugal. The efferent fibres lie in the anterior roots of the spinal nerves, and, like all the fibres there, are either motor or secretory. They are the motor paths for the unstriped muscle of the vessels and viscera, and the secretory paths for the cells of the viscera. In the course of each fibre from the nerve cell in the spinal cord, of which it is an axon, to the vessel or viscus it supplies, there is always a break where it arborizes round a ganglion cell, and this may be in its own ganglion of the sympathetic chain, in a neighbouring ganglion above or below, or in one of the so-called collateral ganglia interposed between the sympathetic chain and the viscera.
The grey rami communicantes are found in connection with all the spinal nerves, though they are irregular in the paths by which they reach the sympathetic ganglia from the cells of which they spring ; their fibres are mainly non-medullated, and pass into both roots of the spinal nerves and also into the anterior and posterior primary divisions of those nerves. In this way they reach the body wall and limbs, and are somatic vasomotor, secretory and pilo motor fibres, supplying the vessels, glands and hair muscles of the skin and its glands.
In the gangliated chain there is a ganglion corresponding to nearly each spinal nerve, except in the neck, where only three are found; of these the superior cervical ganglion is more than an inch long, and is connected with the first four spinal nerves as well as with the ninth, tenth and twelfth cranial nerves (fig. 5). Branches of distribution pass from it to the pharyngeal plexus, the two-fourth sacral ganglia are united by transverse inter f unicular commissures. The white rami communicantes, already mentioned as the pelvic stream, from the second to the fourth sacral spinal nerves, do not enter the ganglia but pass directly to the pelvic plexuses (fig. 6).
In the abdomen the solar plexus is by far the most important.
It lies behind the stomach and surrounds the coeliac axis; in it are situated the semilunar, aortico-renal and superior mesenteric ganglia, and from it are prolonged subsidiary plexuses along the main arteries, so that diaphragmatic, suprarenal, renal, spermatic, coeliac, superior mesenteric, aortic and inferior mesenteric plexuses, are recognized. The hypogastric plexus is the continua tion downward of the aortic, and lies just below the bifurcation of the aorta (fig. 6) ; it divides into two branches, which accom pany the internal iliac arteries and are joined by the pelvic stream of white rami communicantes from the sacral spinal nerves and some twigs from the ganglia of the sacral sympathetic to form the pelvic plexuses. These are prolonged to the viscera along the branches of the internal iliac artery, so that haemorrhoidal, vesical, prostatic, vaginal and uterine plexuses are found. By the side of the neck of the uterus in the last-named plexus several the heart and the two carotid arteries. Of these the branch accom panying the internal carotid artery passes to the carotid and cav ernous plexuses, and through these communicates with the spheno maxillary, otic and ciliary ganglia, while the branch to the external carotid communicates with the submaxillary ganglion. The middle cervical ganglion (fig. 5), when it is present, gives rami com municantes to the fifth and sixth cervical nerves, as well as branches of distribution to the thyroid body and heart.
The inferior cervical ganglion (fig. 5) lies behind the sub clavian artery, and, besides the main connective cord, has a loop (ansa Vieussenii) joining it to the middle cervical ganglion in front of that vessel. It communicates with the seventh and eighth spinal nerves, and gives branches of distribution to the heart and to the subclavian artery and its branches, especially the vertebral. The thoracic part of the sympathetic cord has usually eleven ganglia, which receive both white and grey rami communicantes from the spinal nerves (fig. 6); of the former the upper ones run up in the chain and come off from the cervical ganglia as already described, while the lower ones form the three abdominal splanchnics which pass through the diaphragm (q.v.) and join the abdominal plexuses.
The great splanchnic (fig. 6), comes from the sixth to the ninth ganglia, and ends in the semi-lunar ganglion of the solar plexus. The small splanchnic comes from the ninth and tenth, or tenth and eleventh ganglia, and ends in the aortico-renal ganglion of the solar plexus, while the smallest splanchnic comes from the last thoracic ganglion, whether it be the tenth or eleventh, and ends in the renal plexus.
In the lumbar region the gangliated cord is very irregular; there may be four or more ganglia, and these are often fused. Gray rami communicantes are given to all the lumbar spinal nerves, and white ones are received from the first two. Most of the branches of distribution pass to the aortic plexus. The sacral gangliated cord runs down just internal to the anterior sacral foramina; it usually has four small ganglia, and the two cords end by joining the coccygeal ganglion or ganglion impar, though small ganglia are seen. (For the literature of the sympathetic system, see Quain, Anatomy, London.)