286 



THE NERVOUS SYSTEM 



There appears to be no area in the cortex devoted to 

 the reception of pain impulses. Irritation of the cortex 

 in man never gives rise to pain, nor does stimulation in 

 animals. According to Head, the optic thalamus is the 

 centre for the reception of crude sensations of pain, and 

 the cortex exercises over this centre an inhibitory effect. 

 When the fibres between the cortex and the thalamus are 



CONSCIOUS IMPULSES 

 OF POSITION AND 

 PASSIVE MOVEMENT 



UNCONSCIOUS 



IMPULSES 



(RESPONSIBLE. 



FOR. 

 C0-OR.DINATION| 



UNCONSCIOUS 



IMPULSES 



RESPONSIBLE 



FOR. 



iCO-ORDINATION 



TOUCH AND PRESSURE 



Fig. 45. — Diagram to illustrate the main conucctions of a posterior root 

 and the transmission of sensations up the cord (after Page May). 



destroyed there follows a condition, known as thalamic 

 over-reaction, in which pain is felt to be abnormally 

 intense and to have a disagreeable character. On this 

 view the function of the cortex is to modify this crude 

 sensation and to give it a discriminating and intellectual 

 stamp. 



2. VISION 



The eyeball has three coats — from without inwards, the 

 sclerotic (protective layer), choroid (vascular layer) and 



