118 NERVOUS SYSTEM. 



guish between automatism and reflex action. This automatic action 

 cannot be considered as at all the same as an action of the brain 

 proper, like volition, but rather as a high grade of reflex action. 



What other functions are attributed to the medullary centres ? 



The control or inhibition of action through the nerves which are 

 distributed from this region and through the communications with 

 other centres in the cord. Further than this, there are supposed 

 to lie in the medulla centres which maintain the nutrition and tone 

 of the muscles. These are known as control and tonic centres. 



Name some of the reflex functions depending upon the centres in 

 the medulla. 



(1) The portion of digestion which is performed in the mouth is 

 dependent upon medullary reflexes mastication, deglutition, and 

 the secretion of saliva, and, probably, of the pancreatic and other 

 digestive juices. In this connection the so-called vomiting centre 

 may be noted. 



(2) The respiratory functions are so-called automatic functions 

 of the medulla, and are capable of being sustained by the nerve- 

 force derived from the medulla alone. The centres for coughing 

 and sneezing are also here. The pneumogastric and phrenic nerves 

 convey the afferent and efferent stimuli, though there may be 

 communications with other nerves whereby sensory stimuli are 

 applied. 



(3) Regulation of the heart's action is found here, both inhibitory 

 and accelerator centres communicating through the vagus. 



(4) Vaso-motor, regulation of the unstriped muscular fibre 

 of the arteries is also accomplished by the medulla. A peculiar 

 vaso-motor disturbance is brought about by injury of one centre of 

 the medulla namely, the interference with the glycogen-function 

 of the liver and the appearance of sugar in the urine the diabetic 

 centre. 



(5) Various centres which have to do with the regulation of the 

 body-temperature. The vaso-motor centres we have already men- 

 tioned. There are also found special sz^eotf-centres ; and, further- 

 more, a control of the special sweat-centres found in the cord is 

 here maintained. Upon plausible theoretical grounds there is also 

 assumed to be a heat -inhibitory centre, by which the heat-produc- 

 tion is controlled without reference to vaso-motor conditions. 



