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INTRODUCTION TO NEUROLOGY 



terminates in synaptic relation with some neuron whose cell 

 body lies in the spinal ganglion, which, in turn, may transmit this 

 visceral impulse into the spinal cord in addition to its own proper 

 function, say, of cutaneous sensibility. 



spinal ganglion 



peripheral 

 nerve 



Fig. 109. Diagram illustrating three ways in which afferent visceral 

 fibers may connect with the central nervous system through the spinal 

 ganglia (cf. Fig. 56, p. 126). Neurons 1 and 2 are typical somatic sensory 

 neurons, whose peripheral fibers reach the skin. Neuron 3 is a visceral 

 sensory neuron, whose peripheral fiber enters the sympathetic nervous sys- 

 tem through the communicating branch (this neuron is drawn in fine dotted 

 lines in Fig. 56). Neurons of the third type may bring in afferent impulses 

 from the viscera through their peripheral processes and transmit these im- 

 pulses directly to the spinal cord through their central processes. A col- 

 lateral branch from this neuron, moreover, may carry the visceral impulse 

 to the cell body of a neuron of type 1, which thus serves to convey both 

 somatic impulses from the skin and visceral impulses from some deep-seated 

 organ. The spinal ganglion also receives nerve-fibers of the type marked 4, 

 whose cell bodies lie in the sympathetic ganglia. These probably convey 

 visceral afferent impulses as far as the spinal ganglion, which are then trans- 

 mitted to the spinal cord through a somatic sensory neuron. These arrange- 

 ments are described in detail by Dogiel. 



The relations just described probably provide the neurological 

 mechanism of some of the curious phenomena known as referred 

 pains. It is well known that disease of certain internal organs 

 may be accompanied by no pain at the site of the injury, but by 

 cutaneous pain and tenderness in remote parts of the body. 

 Fig. 110 illustrates some of these areas of referred pain and the 



