CHAPTER XI. 



REFLEX ACTION IN MAN. 



There are in general three types of reflexes elici table in man and 

 the higher mammals. These are: 1. The reflex movements pro- 

 duced by the application of hurtful or nocuous stimuli to the skin 

 (nociceptive reflexes). 2. The reflexes required to maintain the 

 joints in such a position that the animal may stand erect and move 

 about (postural reflexes). 3. So-called myotatic reflexes which are 

 contractions produced by direct mechanical stimulation of muscles 

 that have been brought into a hyperexcitable condition (hyper- 

 tonus) through reflex action. 



An example of nociceptive reflexes is the flexion reflex already 

 studied in the spinal frog. In man this type of reflex, variously 

 modified according to the part of the body from which it is elici- 

 ted, is extensively employed in the diagnosis of nervous diseases. 

 The particular value of the reflex is that its presence or absence 

 indicates the condition of the reflex pathway at the various levels. 

 For the study of reflex time it is useful to employ the palpebral 

 reflex, but in doing so it must be remembered that there are several 

 fundamental differences between this and the flexion reflex, such 

 as the relationship between strength of stimulus and latent time as 

 well as intensity of response. 



Experiment 46. By means of a strip of adhesive tape attach a 

 thread to the upper eyelid. Pass the thread through the handle 

 of scissors which have been clamped to a stand to serve as a 

 pulley. Attach the thread to a heart lever. The head should 

 be held firmly in such a position that when the upper eyelid 

 is closed the writing point of the lever moves upward. To elicit 

 the reflex the subject presses a pair of electrodes against the 

 lower lid. The operator stimulates the subject with break 

 shocks only, using a current which is just strong enough to cause 

 the upper lid to move. The subject must not see the operator 

 at work. With the aid of a magnetic signal determine the reflex 

 time on a rapid clock-work drum. Calculate the average reflex 



104 



