A text-book of physiology, for medical students and physicians . vasoconstrictor fibers are present in numerous nerve THE VASOMOTOR NERVES. 587 trunks, but especially in those distributed to the skin and to theabdominal and pelvic organs. If, for instance, the sciatic or thesplanchnic nerve be cut, to avoid reflex effects, and the peripheralend be stimulated, there will be a strong constriction of the vessels,which may be detected by ocular inspection, blanching; by theincrease in arterial pressure; or by the diminution in volume of theorgans. The vasoconstrictor fibers supplying these two gre
A text-book of physiology, for medical students and physicians . vasoconstrictor fibers are present in numerous nerve THE VASOMOTOR NERVES. 587 trunks, but especially in those distributed to the skin and to theabdominal and pelvic organs. If, for instance, the sciatic or thesplanchnic nerve be cut, to avoid reflex effects, and the peripheralend be stimulated, there will be a strong constriction of the vessels,which may be detected by ocular inspection, blanching; by theincrease in arterial pressure; or by the diminution in volume of theorgans. The vasoconstrictor fibers supplying these two greatregions arise immediately (postganglionic fibers) from one or otherof the ganglia constituting the sympathetic chain, or from the largeprevertebral ganglia (celiac ganglion, for instance) directly con-nected with it. Ultimately, of course, they arise in the centralnervous system (preganglionic fiber), and it has been shown that,for the regions under consideration, they all, with a few compara-tively unimportant exceptions, leave the spinal cord in the great. Fig. 242. —Schema to show the path of the preganglionic and postganglionic portionsof a vasoconstrictor nerve fiber: a, Anterior root, showing the course of the preganglionicfiber as a dotted line; d, v, dorsal and ventral branches of the spinal nerve; r, the ramuscommunicans; g, the sympathetic ganglion. The postganglionic fibers in each ramus comefrom the sympathetic ganglion with which it is connected. The preganglionic fibers enter-ing at any ganglion may pass up or down to end in the cells of some other ganglion. outflow that takes place in the thoracic region from the secondthoracic to the second lumbar nerves (p. 248). In this outflowthey are mixed with other autonomic fibers, such as the sweatfibers, pilomotor fibers, accelerator fibers to heart, pupilodilatorfibers, visceromotor fibers, etc. Emerging in the anterior roots, theypass to the sympathetic chain by way of the corresponding ramuscommunicans. Having re
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