Tendon-reflexes 



221 



Patellar tendon-reflex. The leg being crossed over the opposite 

 knee, and the ligamentum patellae being sharply struck with the inner 

 border of the hand, an afferent impulse is conveyed by filaments of the 

 anterior crural to the lumbar enlargement, and, being there converted 

 into a motor wave, the quadriceps femoris is set in action and the leg 

 is extended with a 'jerk.' Absence of the jerk is evidence of a flaw 

 either in the sensory fibres of the nerve, in the posterior column of the 

 cord, in the grey crescent, or in the motor filaments of the nerve. Thus, 

 it is lost in locomotor ataxy when the posterior external column is 

 sclerosed, and when in diphtheria or infantile paralysis there has been 

 a serious disturbance in the anterior cornu of the crescent. Some- 

 times it will manifest itself only when the patient occupies his muscles 

 and his attention by tightly linking his hands and trying to pull them 

 asunder {Jendrassi&s method]. 



The reflex is exaggerated in disease of the antero-lateral columns, 

 and when the control is lost in cerebral disease, as, for instance, in 

 hemiplegia. 



Ankle-clonus (K\OVO$, any violent motion}. When, the knee 

 being slightly bent, the foot is flexed to a right angle, and is then 

 kept in the over-flexed position by pressing the hand beneath the 

 metatarsal bones, rhythmic contractions and relaxations of the calf- 

 muscles ensue. Afferent and efferent branches (sural) of the internal 

 popliteal, associated in the lumbar en- 

 largement, constitute the reflex chain, 

 and tension in the muscle irritates the 

 nerve and stimulates immediate con- 

 traction. In the case of irritability of 

 the cord, a series of rhythmical con- 

 tractions are set up when the muscle 

 is merely held in the strained position 

 without any sudden flexion of the foot 

 being required to start them. 



The ten do Achillis jerk is shown 

 by striking the tendon when the foot is 

 placed in the flexed position, and the 

 peroneal reflex is obtained in a similar 

 way when the foot is inverted. 



In the upper extremity deep reflexes 

 may be searched in connection with 

 the triceps, biceps, supinator longus, 

 and wrist. 



Transverse section of the cord. 

 The anterior median column con- 

 sists of those fibres which come straight 

 from the anterior pyramid ; it is therefore called the direct pyramidal 

 tract. It is well to remember that it also bears the name of Tiirck. 



Columns of the cord. (GRAY.) 



