772 THE COURSE OF THE VASODILATOR NERVES. 



The Course of the Vasodilator Nerves. The vasodilators pass to some organs 

 as special nerves, while to other parts of the body they are distributed, in asso- 

 ciation with vasoconstrictor and other nerves. The buccofacial region receives 

 dilators in part from the medulla oblongata directly through the trigeminus, and 

 in part from the spinal cord. The latter, according to Dastre and Morat, make 

 their exit with the first, second and third dorsal nerves (in the dog) and pass 

 through the visceral branches (limb of the loop of Vieussens) into the sympa- 

 thetic cord, then to the superior cervical ganglion and, finally, thence through the 

 carotid plexus to the Gasserian ganglion of the trigeminus. The retina receives 

 vasodilator nerves through the sympathetic and the trigeminus; the ear from the 

 first dorsal and the inferior cervical ganglion; the brain from the sympathetic; 

 the heart through the sympathetic and less through the vagus; the upper ex- 

 tremity from the thoracic sympathetic; the lower extremity from the posterior 

 roots ,of the origin of the sciatic. The vasodilators for the submaxillary and 

 sub lingual glands pass in the chorda tympani, as do also those for the anterior por- 

 tion of the tongue. Those for the posterior portion of the tongue are contained 

 in the glossopharyngeus, those for the thyroid gland in the laryngeal branches of 

 the vagus, those for the liver in the splanchnic, those for the pancreas in the 

 vagus, those for the small intestine in the splanchnic, those for the kidney in 

 the vagus. The lungs (in the rabbit) receive dilators from the cervical sympa- 

 thetic; according to Henriques (in dogs and rabbits) from the vagus. Irritation 

 of the nervi erigentes arising from the sacral plexus causes erection through dilata- 

 tion of the arteries of the penis. The muscles receive the dilator fibers for their 

 vessels through the trunks of the motor nerves. If the muscle-nerves or the 

 spinal cord be irritated, the lumen of the vessels undergoes dilatation during the 

 contraction of the muscle-fibers. The latter phenomenon appears even when the 

 contraction of the muscles is prevented. The vasodilators remain medullated 

 out to the terminal ganglia. 



The vasodilators have subordinate centers in the spinal cord, as do the vaso- 

 motors; for example the fibers of the buccolabial region at the level of the first, 

 second and third dorsal vertebras. These can be influenced reflexly through 

 the pulmonary fibers of the vagus, but also through the sciatic nerve. According 

 to Goltz, a similar center is situated in the lower portion of the spinal cord, reflex 

 irritation of which can be induced through the visceral nerves. The portion of 

 the cerebral cortex having vasodilator functions is described on p. 789. 



Goltz showed, in 1874, that vasomotors and vasodilators are situated side by 

 side in the trunks of the extremities, for example in the sciatic (through the inter- 

 mediation of the sympathetic) . If the peripheral stump of this nerve is irritated 

 immediately after division the action of the vasomotors predominates. If, how- 

 ever, the peripheral stump is irritated in the course of from four to six days, 

 during which time the vasoconstrictors will have lost their irritability, the ves- 

 sels become dilated in consequence of the action of the vasodilators. Irritants 

 affecting the nerves at long intervals stimulate especially the vasodilators. Tetan- 

 izing irritants, however, stimulate the vasoconstrictors. The latent period of the 

 vasodilators is longer and they are also more readily exhausted than the vaso- 

 constrictors. Reduction in temperature lowers the irritability of the vasodilators 

 in lesser degree than that of the vasomotors. Exposure of the nerves directly to 

 high degrees of temperature (up to 50 C.) causes irritation of the vasodilators 

 for a long time, as do also closing and opening, as well as permanent continued 

 passage, of the constant current. The phenomena described (which have been 

 observed by Goltz, Heidenhain and Ostroumoff, Putzeys and Tarchanoff and 

 others) can be explained by assuming that the ganglia situated in the vessels, in 

 analogy with the automatic ganglia of the heart, are influenced through both 

 sorts of vascular nerves, the vasoconstrictors causing excitation, the vasodilators 

 inhibition of the activity of these ganglia. 



Certain nerve-trunks contain fibers through which reflex dilatation of vessels 

 can be induced, and, in addition, others through which reflex vasoconstriction can 

 be brought about. The former are less sensitive to cold, are more irritable and 

 regenerate more quickly after injury. 



Irritation of the loop of Vieussens gives rise to pseudomotor contractions in 

 the muscles of the face paralyzed in consequence of destruction of the facial nerve, 

 in the same way as does irritation of the chorda tympani in the tongue paralyzed 

 in consequence of section of the hypoglossus. 



In an analysis of the phenomena related to the vessels, inquiry should be 

 directed especially to determine whether such dilatations as may be present and 



