72 



CONSCIOUS NERVOUS OPERATIONS 



appropriated to vision. The nervous irritation is con- 

 ducted by the optic nerve to that part of the brain con- 

 cerned in perception by means of the eye. The nervous 

 center is affected, and the nervous impulse is passed on, 

 by some unknown process which we speak of as the action 

 of the will, to the nerve fibers running down the white 

 columns of the spinal cord. These convey the impression 

 to the anterior horn of the gray matter of the cord, where 

 lie the motor cells from which arise the motor roots of the 

 spinal nerves. From the motor cells a new nervous 

 impulse goes forth to certain muscles of the arm and 

 hand. The muscular cells of such muscles contract, the 

 bones are moved at the joints, and the apple is seized. 

 This is voluntary muscular action. 



93. Reflex Movement. The voluntary muscles often act 

 without receiving any nervous impulse from the brain, 



Fig. 48. Diagram of the path of a simple nervous reflex action. 



and without any conscious purpose. Suppose the man in 

 putting out his hand to take the apple is stung upon the 

 finger by a wasp not before perceived. The end organ 

 of sensation in the finger sends the impression of paiu 



