Chap. XIX] 



SUMMARY 



401 



A careful study of Figs. 189 and 190 will make the typical 

 reflex path perfectly intelligible to the student, and should on no 

 account be omitted. 



All nervous action is fundamentally similar to this typical 

 reflex action. Usually the number of neurones involved is greater, 

 often very much greater, than two. The fewer the neurones, 

 the simpler and more obviously machine-like the reaction. The 

 more complex the path, the more uncertain and variable the 

 reaction. When the path of the impulse does not involve the 

 cerebrum, the reactions are unconscious and comparatively sim- 

 ple ; but if the cerebral cortex be involved, the passage of the 

 nerve-impulse is accompanied by the phenomenon of conscious- 

 ness, and the reaction may be exceedingly complex, uncertain, 

 and long delayed. These are the characteristics of what we call 

 voluntary reactions. But, although the phrase " reflex action " 

 is usually confined to those actions which are involuntary and 

 of which we are unconscious, yet all nervous action is essentially 

 the same, differing only in the complexity of the path followed 

 by the impulse. 



Nervous 

 System 



Parts of 

 Nervous 

 System 



Func- 

 tions 



Divisions < 



SUMMARY 



Brain. 

 Spinal cord. 

 Sympathetic ganglia. 

 Nerve-trunks. 

 Organules. 

 ■ Makes possible mental activities. 

 Recognition of surroundings and accommodation 



to same. 

 Motion and sensation. 

 Equilibrium and coordination. 

 Brain. 

 Spinal cord. 



C Cerebro-spinal. 

 Nerves < Cranial nerves. 

 I Spinal nerves. 



1. Vertebral ganglia. 



2. Collateral ganglia. 



3. Terminal ganglia and plexuses. 



4. Sympathetic ganglia in the 

 brain and cord. 



Central ner- 

 vous sys- < 

 tem 



SjTnpathctic 

 system 



2d 



