Chap. 16 CONDUCTION AND COORDINATION NERVOUS SYSTEM 291 



must be produced at the synapse before the motor nerve cell receives and 

 transmits an impulse. 



The Nervous System of Vertebrates 



The nervous system is complex but its parts work together in complete 

 unity. It is divided only on the basis of location, special function, and con- 

 venience of description. The central nervous system is the spinal cord and 

 brain; the peripheral system includes the spinal and cranial nerves and their 

 branches, all of the surface nerves; the autonomic nerves control involuntary 

 functions, especially those of the internal organs (Figs. 16.12, 16.13, 16.15). 



Peripheral Nerves 



The trunks of the peripheral nerves issue from the brain and cord. Their 

 large branches extend through the arms and legs and the walls of the body 



Fig. 16.12. A general rear view of 

 the human nervous system. It pre- 

 sents the brain and certain of the 

 cranial nerves, chiefly the facial ones, 

 the spinal cord and the spinal nerves 

 that divide and subdivide extending 

 to every part of the body. The fusions 

 of nerves at the shoulder and hip 

 levels are called the brachial and 

 lumbarsacral plexuses, respectively. 

 (From Vogel: Der Mensch. Leipzig, 

 Barth, 1930.) 



