426 



ORGAN SYSTEMS OF MAN 



collaferal 



syrppafbet'ic 



gcinglion 



Fig. 16-23. A schematic drawing of the nerve pathways Involving the autonomic nervous system. Impulses arising 

 from a temperature sense organ in the skin can stimulate sweating. Also impulses arising from the stomach can 

 cause some action in other parts of the viscera. 



system have a chain of at least two neurons 

 between the central nervous system and the 

 organ innervated, whereas in the voluntary 

 system there is but one. The former are also 

 without a myelin sheath. 



The first autonomic cell bodies of the 

 efferent neurons lie in the lateral portion of 

 the gray matter of the cord, while the sec- 

 ond neuron cell bodies lie outside of the 

 cord in the ganglia already mentioned; 

 sometimes the second ganglia lie directly 

 on the organ itself some distance from the 

 sympathetic chain. The second neuron may 

 return to the ventral root and pass along 

 with the spinal nerve fibers to such parts of 

 the body as the blood vessels of the skin 

 and sweat glands which are under the con- 

 trol of the autonomic nervous system. Others 

 may pass through to a large ganglion ( col- 

 lateral sympathetic ganglion) outside the 

 sympathetic chain where synapsis occurs 



with the second neuron. Fibers leading 

 from the central nervous system to tlie gan- 

 glia outside the cord are called pregan- 

 glionic fibers, those leaving the ganglion, 

 the postganglionic fibers. Such a system of 

 fibers makes it possible for stimuli to come 

 from the internal organs and to effect a re- 

 sponse elsewhere in the body. For example, 

 an impulse can come from the stomach 

 (Fig. 16-23), causing some action to occur 

 in the duodenum, initiating a peristaltic 

 wave, perhaps. Moreover, pain impulses 

 might come from the stomach which, by the 

 intermingling of the two systems (central 

 and autonomic), project through to the 

 cerebral cortex where they are registered as 

 an uncomfortable feeling about which some- 

 thing might be done. Likewise, impulses 

 might arise in the temperature end organs 

 of a too warm skin and pass through the 

 circuits (Fig. 16-23) giving rise to efferent 



