The Nervous System. 



27 1 



respiratory movements and the contraction of the heart 

 are automatic impulses. 



Augmentation and inhibition in a nerve centre is the power 

 it possesses of increasing or decreasing a reflex or auto- 

 matic movement. 



Fig. 26.— Diagram of the Decussation- of the Conducting 

 Paths in the Cord for Sensation and Voluntary Movement. 



R, right side ; L, left side of cord. Sup. r. superior root with its gan- 

 lion a, the fibres crossing over to the opposite side of the cord 

 and so reaching the medulla mo. Inf. r, inferior root, the path for 

 which decussates in the medulla and runs down the same side of 

 the cord. The arrows indicate the direction of the nervous 

 impulses. The places. 1. 2, 3, indicate the effect on motion and 

 sensation of sections made in one-half of the spinal cord at 

 different levels. (After Brown Srquard, and Kirke.) 



B}* Co-ordination is understood the impulses proceeding 

 from nerve centres which regulate the action of a part, and 

 assist in producing a proper sequence of events : for 

 example, in walking the contraction of groups of muscles 



