EFFERENT PATHS AND REFLEX ARCS 



331 



travel along the descending fibers, which arise in that nucleus, to the primary 

 motor neurons of the spinal cord that give rise to the fibers innervating the dia- 

 phragm and abdominal muscles. At the same time the musculature of the 

 stomach is excited to contraction by that part of the wave of excitation which 

 reaches the dorsal motor nucleus of the vagus. These impulses reach the mus- 

 culature of the stomach over the visceral efferent fibers of the vagus and an 

 intercalated postganglionic neuron. 



A similar neural circuit is probably responsible for reflex coughing. From 

 the irritated respiratory mucous membrane, as, for example, of the larynx, the 



Vagus ganglion 



Intercostal muscle 



Diaphragm 



Stomach 



Dorsal motor vagus 

 nucleus 



Nucleus of fasciculus 

 solilarius 



Fasciculus solitarius 

 Tr. solitariospinalis 



Phrenic nerve 

 Intercostal nerve 



Nerve to abdominal 

 muscles 



Sympathetic ganglion 

 Postganglionic 



Fig. 246. Reflex mechanism of coughing and vomiting. (Herrick, Cajal.) 



disturbance is propagated along the afferent fibers of the vagus, through the 

 nucleus of the tractus solitarius and the descending fibers arising in it to the 

 spinal primary motor neurons, which innervate the diaphragm and the inter- 

 costal and abdominal muscles. 



The corpora quadrigemina are important reflex centers. The path for re- 

 flexes in response to sound begins in the spiral organ of Corti and follows the coch- 

 lear nerve and its central connections, including the lateral lemniscus, to the 

 inferior colliculus of the opposite side, and to a less extent of the same side also 



