CHAPTER XVII 



ANATOMY AND PHYSIOLOGY OF THE 

 NERVE SYSTEM 



THE nerve system is divided for the purpose of 

 description into the cerebrospinal and sympathetic 

 systems. The cerebrospinal system consists of the 

 central nerve axis (brain and spinal cord), and the 

 peripheral nerves (cranial and spinal). 



THE STRUCTURE OF THE NERVE SYSTEM 



Neurone, or Nerve Cell Element. The essential 

 structure from which all the functions of the human 

 body arise as a result of innervation, is the cell ele- 

 ment called the neurone. They differ from all the 

 other cells in the tissues, in that their protoplasm 

 is extended in the form of processes, and these 

 reach some distances from the nuclear portion of the 

 cell. , 



The neurones are the essential structures concerned 

 in all nerve reflex. However, the fact of a sensor 

 impulse reaching a neurone from a muscle, gland, or 

 other cell, does not say a motor impulse will be returned 

 from the neurone direct, as the neurones are connected 

 with other neurones by means of their extending 

 processes, which have the power of reacting and 

 sending out excitomotor impulses, and of checking 

 or reducing the impulse to the structure to be inner- 

 vated. 



