CHAPTEK IV 



GENEKAL PHYSIOLOGY OF THE NERVOUS SYSTEM 



CONTENTS. 1. Structural elements of the nervous system. Theory of in- 

 dependent neurones, or continuity of neuro-fibrils. 2. Conditions, laws and 

 phenomena of conduction in nerve. 3. Rate of conductivity : diphasic character 

 of the impulse arousing it. 4. Metabolism of nerve ; electromotive phenomena 

 during rest and excitation : demarcation current, action current. 5. Excitation 

 of nerve. Natural stimuli and artificial (chemical, mechanical, electrical) stimuli. 

 6. Factors in life and death of nerve : conditions of excitability. 7. Polar effects 

 of constant current (electrotonus) : correlative changes in excitability and con- 

 ductivity. 8. Excitatory action of electrical currents. Laws of excitation. 

 9. Theories as to origin of nerve activity. 10. General functions of nerve-centres. 

 Ganglion cells and central fibrillary network. Bibliography. 



THE Nervous System, which is the real centre of the functions of 

 animal life, controls the activities of the organs of involuntary 

 or vegetative life, as well as those of the muscles. By means of 

 the sensory mechanisms it correlates the several organs among 

 themselves, and brings the organism as a whole into relation with 

 the external world, while it is able by means of the motor 

 mechanisms to vary these relations and adapt them to change of 

 circumstances. 



In order that it may fulfil these important functions, the 

 nervous system is built up of morphological elements which 

 establish a functional link between the different organs, inde- 

 pendent of their juxtaposition or distance, and control the 

 circulation of the tissue fluids, so that when a given change takes 

 place in one part, other phenomena necessarily ensue in other 

 remote parts, e.g. in the skin and the muscles, the mucous 

 membrane and the glands, etc. It is the nervous system that 

 presides over those complex relations between distant organs 

 which the ancients termed " sympathies." It represents the 

 physiological unity, the reciprocal dependence of parts, on which 

 the psychological unity, expressed in the phenomena of the ego or 

 consciousness, is founded. 



The most elementary organisms, while they possess no differ- 

 entiated nervous and muscular systems, nevertheless exhibit 

 essential animal characteristics of sensibility and motility, albeit 



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