CH. XL1X.] REFLEX ACTION IN MAN 711 



hence the part of the cord below the injury having it, as it were, all 

 its own way, has its reflex irritability increased.* The increase of 

 reflex irritability is also seen in the disease called lateral sclerosis; 

 here the lateral columns, including the pyramidal tract, become 

 degenerated, and so the path from the brain to the cells of the cord 

 is in great measure destroyed. In these patients the increase of 

 reflex irritability may become a very distressing symptom, slight 

 excitations, like a movement of the bed-clothes, arousing powerful 

 convulsive spasms of the legs. 



Reflex Action in Man. 



The reflexes obtainable in man form a most important factor 

 in diagnosis of diseases of the nervous system ; each action is effected 

 through an afferent sensory nerve, a system of nerve-cells in the 

 cord termed the reflex centre, and an efferent motor nerve; the 

 whole constitutes what is called the reflex arc. The absence of 

 certain reflexes may determine the position in the spinal cord which 

 is the seat of disease. 



Two forms of reflex action must be distinguished : 



1. Superficial reflexes. These are coordinated reflex actions, and 

 are excited by stimulation of the skin. 



2. Deep reflexes or tendon reflexes. 



Superficial Reflexes. These are obtained by a gentle stimula- 

 tion, such as a touch on the skin ; the muscles beneath are usually 

 affected, but muscles at a distance may be affected also. Thus a 

 prick near the knee will cause a reflex flexion of the hip. 



The most important of these reflexes are : 



a. Plantar reflex: withdrawal of the feet when the soles are 

 tickled. 



b. Grluteal reflex : a contraction in the gluteus when the skin over 

 it is stimulated. 



c. Cremasteric reflex : a retraction of the testicle when the skin on 

 the inner side of the thigh is stimulated. 



d. Abdominal reflex: a contraction of the muscles of the 

 abdominal wall when the skin over the side of the abdomen is 

 stroked ; the upper part of this reflex is a very definite contraction 

 at the epigastrium, and has been termed the epigastric reflex. 



e. A series of similar reflex actions may be obtained in the muscles 

 of the back, the highest being in the muscles of the scapula. 



f. In the region of the cranial nerves the most important reflexes 

 are those of the eye (i) the conjunctival reflex, the movement of the 



* In some injuries to the cord produced by crushing, there is a loss of reflexes 

 below the injury! These, however, are not simple transverse lesions ; the loss of 

 reflex action is due partly to shock, and partly to extensive injury of the grey matter. 



