850 





lumbar and the second sacral to the fourth sacral nerves. The somatic motor 

 fibers, efferent fibers, arise from cells in the anterior column of the spinal cord and 

 pass out through the anterior roots to the voluntary muscles. The sympathetic 

 efferent fibers, probably arise from cells in the lateral column or the base of the 

 anterior column and emerge through the anterior roots and white rami communi- 

 cantes. These are preganglionic fibers which end in various sympathetic ganglia 

 from which postganglionic fibers conduct the motor impulses to the smooth muscles 

 of the viscera and vessels and secretory impulses to the glands. These fibers are 

 also limited to two regions, the first thoracic to the second lumbar and the second 

 sacral to the fourth sacral nerves. 



The afferent fibers which pass into the spinal cord establish various types of 

 connections, some within the cord itself for spinal reflexes, others for reflexes con- 

 nected with higher centers in the brain, while still others conduct impulses of 

 conscious sensation by a series of neurons to the cerebral cortex. 



pina! lemniscus 

 correlation neurone! 

 fumculus dorsalis 



spg.l 



correlation neuroneS 

 sp. g. 2 



s Kin 

 sp g.5 



correJaTion neurone^ 

 (j sp.g.4 



FIG. 758. Diagram of the spinal cord reflex apparatus. Some of the connections of a single afferent neuron from 

 the skin (d.r.2) are indicated: d.r.2, dorsal root from second spinal ganglion; m, muscles; sp.g.l to sp.gA, spinal 

 ganglia; v.r.l 1 to v.rA, ventral roots. (After Herrick.) 



The Intrinsic Spinal Reflex Paths. The collaterals and terminals of the ascend- 

 ing and descending branches of the posterior root fibers which leave the fasciculus 

 cuneatus to enter the gray matter of the spinal cord end in various ways. Many end 

 in the dorsal column, some near its apex, others in the substance of Rolando, others 

 in the intermediate region between the dorsal and ventral columns, others traverse 

 the whol 3 thickness of the gray matter to reach the ventral column, others end in the 

 dorsal nucleus, and others pass through the gray commissure to the dorsal column 

 of the opposite side. All of these collaterals and terminals end in connection with 

 cells or dendrites of cells in the gray columns. The axons of these cells have various 

 destinations, some pass out into the lateral and ventral funiculi and turn upward 

 to reach the brain. Those concerned with the intrinsic spinal reflexes come into 

 relation either directly or indirectly with motor cells in the anterior column. It is 

 very unlikely that either the terminals or collaterals of the dorsal root fibers effect 

 simple direct connections with the motor cells of the ventral column, there is at 

 least one if not several intercalated neurons in the path. These intercalated or 

 correlation neurons may have short axons that do not pass out of the gray matter 

 or the axons may pass out into the proper fasciculi and extend for varying distances 



