NEXTROLOGY 301 



periphery. The function of the inferior roots is to supply all the 

 voluntary muscles as well as the oviduct, the intestines, and other 

 hollow viscera, including the blood-vessels with the power of move- 

 ment. Many of these fibers pass to the sympathetic ganghon and 

 are distributed as sympathetic nerve fibers. 



The cord is divided into different tracts, that is, certain groups 

 of fibers convey certain kinds of impulses. 



The superior column of the cord conveys to the cerebrum such 

 impressions as temperature, pressure, and muscular tension. 



The fibers of the lateral columns carry sensations of pain. 



The fibers of the direct cerebellar tract carry impulses which 

 result in the maintenance of the equiUbrium of the body. 



All the voluntary impulses originate in the. cerebrum, pass through 

 the cerebellum and travel direct to the bulb; they then pass over 

 to the opposite side, and travel by the crossed pyramidal tract to 

 the multipolar cells of the inferior horn of the spinal cord, and trans- 

 mit the impulse through motor fibers that originate at that point in 

 the cord. 



All sensory impulses enter the brain on the side opposite their 

 origin, and all motor impulses leave the brain on the side opposite 

 that to which they are distributed. Injury of the motor area of the 

 right side of the brain leads to paralysis of the left side of the body. 



An impulse of the vasomotor nerve travels in the lateral column 

 of the cord. 



A nerve impulse may originate in the brain and be modified in 

 passing through a ganglion in the spinal cord or in the sympathetic 

 system. 



The system of reflex action is as follows: first, an efferent nerve 

 which conveys the impulse from the periphery to a nerve center; 

 second, a ganghon, or nerve center, to receive the impulse and gen- 

 erate other impulses; third, an efferent nerve to convey the impulse 

 from the nerve center to the periphery. 



The following is an example of reflex action. The foot of a fowl 

 is pierced with a pin. The sensory impulse is conveyed by sensory 

 nerve fibers to the nerve centers. In this center the gangUonic 

 nerve ceUs generate a motor impulse which is sent back through the 

 motor nerve fiber to the muscles controlling the part. The result 

 is that the muscle contracts and jerks the foot. 



There are many functional centers located in the meduUa oblon- 

 gata. Destruction of this part of the system results in instant death 



