712 



FUNCTIONS OF THE SPINAL COKD 



[CH. XLIX. 



FIG. 440. The Knee-jerk. (Gowers.) 



eyelids when the front of the eyeball is touched ; and (ii) the con- 

 traction of the pupil on exposure of the eye to light, and its dilatation 

 on stimulation of the skin of the neck. 



Tendon Reflexes. When the muscles are in a state of slight 

 tension, a tap on their tendons will cause them to contract. The 



tendon reflexes which are 

 generally examined are the 

 patella tendon reflex or knee- 

 jerk, the tendo Achillis reflex 

 or ankle-jerk, and phenomenon 

 known as ankle-clonus. 



The knee-jerk. The quad- 

 riceps muscle is slightly 

 stretched by putting one knee 

 over the other; a slight blow 

 on the patella tendon causes a 

 movement of the foot for- 

 wards, as indicated in the 

 dotted line of fig. 440. The 

 phenomenon is present in 

 health. 



The ankle-jerk is one of 

 great importance, for in such 



diseases as locomotor ataxy, in which the tendon reflexes are lost, it 



usually disappears before the knee-jerk. It is best elicited if the 



patient kneels with one knee 



upon a cushioned chair, whilst 



standing on the other leg by the 



side of the chair. The calf 



muscles of the kneeling leg are 



thus relaxed, and a sharp tap 



upon the tendo Achillis elicits 



the jerk. 



Ankle-clonus. This is eli- 

 cited as depicted in the next 



figure: the hand is pressed 



against the sole of the foot, the 



calf muscles are thus put on the 



stretch and they contract, and 



if the pressure is kept up a 



quick succession or clonic series 



of contractions is obtained. This, however, is not readily obtained 



in health. 



The phenomena depend for their occurrence on the integrity of 



the reflex arc. Disease or injury to the afferent nerve, efferent 



FIG. 441. Ankle-clonus. (Gowers.) 



