5: Sensory Cell Function and 

 Architecture 



A good many problems concerning the relationship between form 

 and function which are common to all neurons may be more 

 conveniently examined in sensory neurons in particular. For 

 example, the nature of the processes involved in impulse initiation 

 in primary sensory neurons presents problems which differ in each 

 cellular morphology and, often, in each neuron population. In 

 particular, a consideration of neuron geometry is critical in terms 

 of logistics as well as the limiting physical properties of the 

 membrane. For example, crustacean stretch receptor neurons 

 have distributed loci which serve a transducer function. These 

 loci are, in fact, the terminations of the numerous dendritic 

 arborizations which are imbedded in the central region of the 

 muscle receptor organs. It is not inconceivable that impulses 

 initiated in one dendrite (by stretch applied to the receptor muscle) 

 might propagate into adjacent dendritic branches, as well as 

 orthodromically toward the central nervous system. Retrograde 

 firing in this fashion would block by collision any impulse activity 

 set up in adjacent branches. One can foresee that, if firing 

 frequency in adjacent branches were unequal, the characteristic 

 frequency from the branch that generated the most impulses per 

 unit time would invariably dominate the output of the cell as a 

 whole. If it happened that stimulus energy were coupled to 

 different dendritic branches in an unequal fashion, equal incre- 

 ments in stimulus energy would surely not be detected as such by 

 the different dendritic branches, and one might conceivably even 

 find a situation where stimulus strength had increased, but the 



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