CHEMORECEPTOR MECHANISMS 



23 



Diagram illustrating the relations of the olfactory- nerve fibers to the neurons of 

 the second order in the olfactory bulb, olf.c, olfactory nerve cells in the olfactory epi- 

 thelium; olf.n., olfactory nerve; mc, mitral cells; gl. olfactory glomeruli; n.tr., olfactory 

 tract. {Schdjer, "Organs of the Senses," Longmans, Green & Co., Inc.) 



Fig. 20. The relation between the olfactory receptors and other neural cells of 

 the olfactory bulb (from McCord and Witheridge, 1949.) 



What would appear most helpful at this time would be an accurate identi- 

 fication of the adequate olfactory stimulus; or, to restate the desideratum as a 

 question, is every receptor sensitive to all odors provided that a critical con- 

 centration can be applied? As in the case of the sense of taste, an electrical ap- 

 proach to the problem appears to be necessary. However, the only successful 

 recordings which have been reported in the literature thus far were obtained 

 with electrodes located in the olfactory tract or bulb several synapses removed 

 from the receptors. 1 Upon the interpretation of the pattern of discharges ob- 

 tained depends the answer to the question of receptor specificity. 



1 Since this symposium was presented three papers have been published, two of 

 which report successful efforts to place electrodes directly on the olfactory receptor 

 fibers. Beidler and Tucker (1955) have succeeded in recording electrically from nerve 

 bundles in isolated opossum nasal epithelium exposed to pure air and odors. Results 

 indicate that one fiber may not respond to a given odor as well as another fiber, al- 

 though this relationship may be reversed if a different test odor is chosen. Walsh 

 (1955) studied unitary activity in the bulb of the rabbit by means of micropipette 

 electrodes. Cells of one type detected by this method responded markedly to stimula- 

 tion by butyl acetate but failed to respond to high concentrations of acetophenone or 

 tertiary amyl alcohol. Schneider (1955) has recorded impulses from single fibers of 

 olfactory receptors in the antennae of male moths being stimulated with the odorous 

 material produced by the sex attractant glands of the female. These results are pre- 

 liminary, and no information relative to the specificity of the different receptors was 

 given. 



