1 70 HUMAN PHYSIOLOGY. 



when the skin between the scapulae is stimulated; it depends upon the 



integrity of the cord between the fifth cervical and third thoracic nerves. 



The superficial reflexes, though variable, are generally present in health. 

 They are increased or exaggerated when the gray matter of the cord is 

 abnormally excited, as in tetanus, strychnia-poisoning, and disease of the 

 lateral columns. 



The tendon reflexes, characterized by the contraction of a muscle, are also of 

 much value in the diagnosis of lesions of the spinal cord and are eh' cited by a 

 sharp blow on a tendon. The following are the principal tendon reflexes: 



1. Patellar reflex, or knee-jerk, consisting of a contraction of the extensor 

 muscles of the thigh when the ligamentum patellae is struck between the 

 patella and tibia. This reflex is best observed when the legs are freely 

 hanging over the edge of a table. The patellar reflex is generally present 

 in health, being absent in only two percent; it is greatly exaggerated in 

 lateral sclerosis and in descending degeneration of the cord; it is absent 

 in locomotor ataxia and in atrophic lesions of the anterior gray cornua. 



2. Ankle- jerk or Ankle Reflex. If the en tensor muscles of the leg be placed 

 upon the stretch and the tendo Achillis be sharply struck, a quick extension 

 of the foot will take place. 



3. Ankle-clonus. This consists of a series of rhythmic reflex contractions 

 of the gastrocnemius muscle, varying in frequency from six to ten a 

 second. To elicit this reflex, pressure is made upon the sole of the foot 

 so as suddenly and energetically to flex the foot at the ankle, thus putting 

 the tendo Achillis and the gastrocnemius muscle on the stretch. The 

 rhythmic movements thus produced continue so long at the tension, with- 

 in limits, is maintained. Ankle-clonus is never present in health, but is 

 very marked in lateral sclerosis of the cord. 



The toe reflex, peroneal reflex, and wrist reflex are also present in sclerosis 

 of the lateral columns and in the late rigidity of hemiplegia. 



Special Nerve Centers in Spinal Cord. Throughout the spinal cord 

 there are a number of spinal nerve centers, capable of being excited reflexly 

 and of producing complex coordinated movements. Though for the most 

 part independent in action, they are subject to the controlling influences of 

 the medulla and brain. 



i. Ciliospinal center, situated in the cord between the lower cervical and 

 the third dorsal vertebra. It is connected with the dilatation of the pupil 

 through fibers which emerge in this region and enter the cervical sympa- 

 thetic. Stimulation of the cord in this locality causes dilatation of the 

 pupil on the same side; destruction of the cord is followed by contraction 

 of the pupil. 



