THE SPINAL CORD 231 



each other, run chiefly in the anterior ground and lateral 

 bundles and the columns of Burdach. 



Classification of the reflexes. The reflex movements executed 

 by the aid of the spinal cord can most readily be studied in cold- 

 and warm-blooded animals in which the action of the brain is ex- 

 cluded by a section between the brain and spinal cord. 



According to the degree of spreading of the reflex move- 

 ment we may discriminate : 



1. Simple or partial reflexes. The stimulation of a 

 sensory spot is followed by the movement of only one 

 muscle or of a limited group of muscles. Example : knee- 

 jerk. If the sensory nerve of the ligamentum patellae is 

 stimulated by hitting the ligament, the quadriceps femoris 

 muscle contracts by reflex action and the lower part of the 

 leg is thrown forward. 



2. Radiated reflexes. Stimulation of a sensory area 

 results in the contraction of large groups of muscles or of all 

 the muscles of the body. We may classify them as: 



(a) Orderly radiated reflexes. The stimulation is fol- 

 lowed by a movement with the purpose of removing the 

 stimulus or fleeing from it. If, for example, the leg of a 

 decapitated frog is moistened with a drop of acid, the frog 

 wipes off the acid; if the foot is pinched or pricked, it tries 

 to flee. These reflectory defensive movements can also be 

 observed in man during sleep. 



The movements appear to us as voluntary movements, 

 but whether they are accompanied by consciousness in the 

 cells of the spinal cord cannot be determined, for we have 

 no knowledge of any subjective perception in the cells. It 

 is of interest to note that the cells of the spinal cord are able 

 independently to change the afferent impulses into a pur- 

 poselike muscular activity and are, therefore, from a physio- 

 logical standpoint, not different from the cells of the cerebral 

 hemispheres in which the psycho-physical processes take 

 place. 



(b) Disorderly radiated reflexes or convulsive reflexes. 



