CHAPTER XI 



STRUCTURE, NERVE CONNECTIONS, AND FUNCTIONS OF 

 THE CEREBRUM 



The Cerebrum Dependent on the Receptor System. If the 

 cerebrum is to introduce remote considerations as factors in de- 

 termining the nature of reflex responses it must have within it the 

 knowledge upon which these remote considerations are based. 

 That the cerebrum has little original endowment of knowledge is 

 evident from study of infants, who during the first months are 

 perfect examples of "reflex" organisms. The equipment which 

 the cerebrum finally obtains must be gotten bit by bit by ex- 

 perience or the teaching of others. Since the receptor system is 

 the organism's only means of acquiring information, the cere- 

 brum must be in communication with this system if it is to learn 

 anything whatsoever. 



Afferent Paths of the Cerebrum. We have learned in previous 

 paragraphs that all sensory neurons lead directly into the central 

 nervous system and there have numerous synaptic connections 

 with association neurons. These connections are all, however, 

 with the possible exception of those of the sense of smell, made 

 in gray matter of the spinal cord, the medulla, or the midbrain. 

 In order for impulses coming in over these sensory neurons to 

 reach the cerebrum there must be communication by association 

 neurons between the terminations of the sensory neurons and the 

 cerebrum. As a matter of fact such connections are richly sup- 

 plied. Some of the most conspicuous tracts of white matter in 

 the central nervous system consist of the myelinated axons of 

 association neurons which form connecting links between sensory 

 neurons and the cerebrum. Since the cerebrum is the crown of 

 the entire nervous system it is used as a landmark in describing 

 other nervous structures. Thus nerve paths which convey im- 

 pulses toward the cerebrum are called afferent paths; those carry- 

 ing impulses away from it are efferent paths. According to this 

 classification all sensory neurons are afferent and all motor ones 



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