NERVOUS SYSTEM IN GENERAL. 



263 



the cerebral cortex in the perception of the sensation 

 and the formation of the volition, (3) the time of conduct- 

 ing the motor impulse and giving the signal. The greater 

 part is in the middle interval, i.e. the central elaboration, 

 during which the entering impression gives rise to an out- 

 going impulse. 



Reflex Action. In a previous diagram of reflex action, 

 a single cell was represented as receiving the afferent im- 



Nerve Cells connected by Interlacing Nerve Network 



Afferent Nerve Fibe 



Sensory 

 Epithelium 



Efferent Nerve Fiber 



Muscle 



Fig. 83. Diagram of Reflex Action. 



pulse and sending out an efferent one. It is more proba- 

 ble that at least two cells are concerned in such an act, one 

 receiving the incoming impulse, and influencing, by means 

 of fine connecting branches, a second cell which sends out 

 the motor impulse, as shown in Fig. 83. 



Connection of Brain Centers. We have_seen that the 

 brain functions. are more or less localized. We also know 

 that the cortex receives impressions through the channels 



