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The Molecular Basis of 

 Nerve Conduction 



I. Donnan Membrane Potentials 



In Chapter 4, the basic phenomena of nerve conduction were described 

 in detail. Their molecular interpretation was deferred to this chapter 

 since it leans heavily on the ideas of active transport, diffusion, perme- 

 ability, and thermodynamics. As a first approach, the expression for 

 the Donnan potential across a membrane will be derived. The 

 remainder of the chapter is concerned with three simplified systems for 

 studying nerve conduction. 



Historically, physics has substituted simplified systems for more 

 complex ones ; after studying the simplified system, the original becomes 

 more understandable. For instance, in mechanics, real machines with 

 friction are described in terms of the behavior of an ideal frictionless 

 machine. In this chapter, three types of simplified systems are dis- 

 cussed ; all of them attempt to study effects which might lead to a more 

 complete understanding of the molecular phenomena involved in the 

 conduction of impulses by nerves. The first system discussed attempts 

 to mimic the rapid spike potential by a subthreshold direct current. 



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