414 PHYSIOLOGY 



Secretory to glands of stomach and to pancreas. 



Afferent functions : 



Regulate respiration. Stimulation of central end may quicken 

 respiration and promote inspiration, or may inhibit inspiration. 

 Stimulation of central end of superior laryngeal branch causes 

 stoppage of inspiration, expiration, cough. 

 Depressor and pressor (from heart to vaso-motor centre). 

 Reflex inhibition of heart. 



Its afferent fibres arise from cells in the ganglia on the frunk of the 

 vagus, namely, the jugular ganglion and the ganglion trunci vagi. The 

 spinal accessory nerve arises partly in connection with the vagus, partly by 

 a series of roots from the lateral region of the spinal cord as low as the sixth 

 cervical segment. The spinal portion of the nerve is purely motor and 

 supplies fibres to the sterno-mastoid and trapezius muscles. 



The twelfth or hypoglossal nerve arises from a collection of large multi- 

 polar cells in the floor of the fourth ventricle at its lower <end close to the 

 middle line. The nerve-trunk issues from the ventral part of the medulla 

 in the groove between the anterior pyramid and the olivary body. The 

 hypoglossal is purely motor in function, supplying the muscles of the tongue, 

 the extrinsic muscles of the larynx, as well as those moving the hyoid bone. 



Since the integrity of the nuclei of the cranial nerves is a necessary con- 

 dition for the carrying out of various reflex acts in which those nerves are 

 involved, the grey matter of the fourth ventricle and aqueduct is often 

 spoken of as if it were cut up into a series of centres distinct for every act. 

 The chief of these are the respiratory and the vaso-motor centres. Other 

 centres that may be enumerated are : 



Centres for movements of intrinsic and extrinsic ocular muscles. 



Cardiac inhibition. 



Mastication, deglutition. 



Sucking. 



Convulsive (connected with respiratory). 



Vomiting. 



Diabetic (connected with vaso-motor). 



Salivary. 



Centres of phonation and articulation. 



We shall have to consider the action of these centres more fully in treating 

 of the several functions of the body. It must be remembered however 

 that, when a dozen or more centres are enumerated as being situated in the 

 fourth ventricle, it is not meant that we can anatomically distinguish a group 

 of cells for each act or group of actions named. When we say that a part of 

 the nervous system is a centre for any action, we merely mean that this part 

 forms a necessary link, or meeting of the ways, in the complicated directing of 

 nerve impulses that takes place in every co-ordinated act, 



