I HAPTER LXXXD5 

 THE REFLEXES OF THE SPINAL ANIMAL AND 



SPINAL SHOCE 



Saving become familiar with the peculiar properties of each of 4 

 structures which go to make up the reflex arc, we may now proceed to 

 consider the function of the arc as a whole. It may be well f all 



to consider briefly the experimental method by which such studies may 

 be made. The object aimed at is to simplify the conditions 

 much as possible, for it will be evident that, in the intact nervous - 



tern, with the brain exercising a dominating influen ver the crreat 



majority of all the reflexes, it would be impossible by applying a given 

 stimulus, to predict exactly what kind of reflex response it might rail 

 forth. The reflex will be conditioned upon the accompanying influei 

 which the brain exercises on the reflex involved. 



In order to render the reflex unconditioned, we must remove the in- 

 fluence of higher centers. This can be done experimentally for the 

 ilexes of a great part of the body by cutting the spinal cord above the 

 level of the segment in which the reflex under investigation resi 

 Some of the reflexes elicitable from the cord isolated in this way in- 

 volve only one or two neighboring segments, whereas others spr< 

 over several. The reflexes which have been most extensively emplo; 

 are those which involve the musculature of the hind limbs. Since some 

 of the receptors concerned come Erom the skin of the flank and shoul- 

 der areas, the section is usually made at the upper end of the thoracic 

 region of the spinal cord. 



Spinal Shock in Laboratory Animals 



Immediately after the operation a profound condition of depn - 



in, involving all the reflex area in the separated portion of cord. This 

 condition is known as s/iiiml shock. It supervenes in all class ani- 



mals having a spin;il cord, but is much more profound in the hi_ 

 than in the lower animals. Afl a result of this depression, the part of 

 the body below the section exists in a limp ami flaccid condition, and the 

 application of even very BtTOng stimuli to the skin will evoke 1 

 of reflex movement. In the case of the lower animals, such as the f 



