ELECTROPHYSIOLOGY 



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the central nervous system, where the impulses are received. 

 The work of the English physiologist Sherrington and of the 

 Russian Pavlov has had to do with this question of the nature 

 of the impulses sent out by the central nervous system in relation 

 to the kinds received by it. Foerster has demonstrated that 

 stimulation of the temporal lobe of the human cortex may cause 

 sounds and words to arise in consciousness and that stimulation 

 of the occipital lobe gives light or images. 



It has been possible to record with remarkable mechanical 

 precision the rhythmic nature of nerve impulses and to gain some 

 knowledge of the chemistry and physics of these impulses. 



Fig. 150. — Record of a train of impulses or action potentials of single nerve fibers. 

 (From D. W. Bronk and H. K. Hartline.) 



Important as are these studies, they still leave us ignorant of the 

 mechanism of the nervous system as a whole, of learning and 

 memory, though these latter have been interpreted by the 

 psychologist K. S. Lashley in terms of a mechanism involving 

 the activity of groups of neurons or cerebral centers. 



Electrolytic Conduction. — The passage of a current through a 

 solution is known as electrolytic, or ionic, conduction in distinction 

 from metallic, or electronic, conduction in a wire. 



Conductance is the reciprocal of resistance; i.e., conductance = 

 1 /resistance. We may, consequently, determine the con- 

 ductivity of a wire or a solution by measuring the resistance. 

 Resistance is measured electrically by the setup known as 

 Wheatstone's bridge. 



In determining the resistance of an electrolytic solution, a 

 direct current cannot be used, because it brings about electrolysis, 

 and readings after one, two, or three minutes will differ. An 

 alternating current must be employed. It is usually supplied 

 by inserting a small induction coil which receives its current 

 from a battery. The use of an alternating current precludes 



