892 



CENTRAL NERVOUS SYSTEM 



neither reflexly nor by volition. Injuries to the pyramidal tracts, how- 

 ever may cause paralysis without affecting the reflex response of the 

 muscles. Consequently an examination of the reflex excitability of the 

 paralyzed muscles will reveal whether the injury involves the motor neu- 

 ron or not. Since, as we shall see (page 951) impulses from the cere- 

 brum may have an inhibitant effect on certain reflexes, disease which 

 cuts off this influence may cause an exaggeration of certain reflex re- 

 sponses. Moreover since these reflexes are carried out over arcs which 

 lie within definite segments of the cord the failure of a reflex may 

 indicate in what part of the cord the lesion lies. 



The segments involved in the more important reflex tests are indicated 

 in the following table : 



LOCALIZATION OF MUSCULAR REFLEX ACTS IN THE SPINAL CORD 



(After Starr) 



Pupillary reflex through the sympathetic: Dilatation 

 of the pupil produced by irritation of the neck. 



Scapular reflex: Irritation of the skin over the scapula 

 produces contraction of the scapular mucles. 



Biceps and supinator longus: Tapping their tendons 

 produces flexion of the forearm. 



Triceps reflex: Tapping tendon produces extension of 

 forearm. 



Scapulohumeral reflex: Tapping the inner lower edge 

 of the scapula causes adduction of the arm. 



Tapping extensor tendons at the wrist causes extension 

 of the hand. 



Tapping flexor tendons at the wrist causes flexion of the 

 hand. 



Palmar reflex: Stroking palm causes closure of fingers; 

 finger clonus. 



Abdominal reflex: Stroking side of abdomen causes 

 retraction. 



Genital reflex: Squeezing the testicle causes contraction 

 of the abdominal muscles. 



Patella tendon: Striking tendon at knee causes exten- 

 sion of the leg; "knee-jerk." 



Achilles tendon reflex: Tapping the Achilles tendon 

 causes flexion of ankle. 



Foot clonus: Extension of Achilles tendon causes flex- 

 ion of the ankle. 



Plantar reflex: Tickling sole of foot causes flexion of 

 toes, or extension of the great toe and flexion of the 

 others. 



Fourth cervical to first dor- 

 sal. 

 Fifth cervical to first dorsal. 



Fifth and sixth cervical. 



Sixth cervical. 



Seventh cervical. 



Sixth to eighth cervical. 



Seventh to eighth cervical. 



Eighth cervical to first dor- 

 sal. 

 Ninth to twelfth dorsal. 



First to third lumbar. 

 Second and third lumbar. 

 First to third sacral. 

 First to third sacral. 

 First to third sacral. 



