PART III 



REFLEX ACTION 



With the exception of the axon-reflexes, already described, 

 all reactions to stimuli in the higher animals occur through 

 the central nervous system. Such reactions are called 

 reflex actions. In order to study them it is necessary to 

 transect the spinal cord in its upper part in order to 

 eliminate influences due to cerebral processes, such as 

 wifled movements. An animal so prepared is known as 

 the spinal animal. For our knowledge of reflex action 

 we are indebted to the researches of Sherrington. 



Examples of Reflex Action : — 



1. The Flexion Reflex. — When the skin of the foot in the 

 spinal animal is pricked, burnt or stimulated electrically 

 the foot is drawn up. 



2. The Extensor Thrust. — When pressure is apphed to 

 the pad of the foot the leg is fully extended. 



3. The Scratch Reflex. — When any point over a wide 

 area of the back and flank is stimulated the hind leg per- 

 forms a rhythmic scratching movement directed to the 

 point stimulated. 



In reflex paths three component parts can be made 

 out : — 



1. A receptor organ, situated peripherally. This struc- 

 ture is endowed not only with a high degree of irritability, 

 but also with the power of responding to stimuU of a 

 particular kind. 



2. An effector organ — muscle or gland, 



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