DYNAMICS OF TASTE CELLS 141 



determined experimentally by recording from a small trigeminal nerve 

 bundle that innervates the olfactory area. These small sensory fibers 

 end in the mucosa as bare nerve endings and their very low firing rate 

 allows the experimenter to analyze in a simultaneous recording as many as 

 7 single fibers that respond to an applied vapor. Such simultaneous 

 recordings indicate that the bare nerve endings are highly sensitive to 

 chemical stimuh and that certain fibers respond best to one type of chemical 

 whereas others respond better to another type. Thus one might expect 

 that bare nerve endings in other tissue also respond well to chemical 

 stimuli and even show some specificity in their response to a number of 

 different types of chemicals. 



Chorda Tympani Nerve Bundles 



The response of a large population of taste buds may be studied by 

 recording from the total chorda tympani nerve bundle. The frequency 

 of nerve impulses from single taste nerve fibers is very irregular and 

 therefore difficult to quantitate. For this reason an integration of the 

 total recorded activity from the chorda tympani nerve bundle is used for 

 many studies (Beidler, 1951). Fishman showed that the results of such 

 integration resembles that of the sum of a number of single fibers (1957). 

 Since the total area under the curve of the recorded action potential is 

 integrated, and since the smaller fibers have a smaller height but a greater 

 width, the disparity in contribution between large and small fibers is not 

 as great as one might expect. Integration is not, however, a useful tech- 

 nique for the study of the physiological basis of taste qualities. 



RESPONSE CHARACTERIZATION 



Temporal Characteristics 



Following stimulation the frequency of nerve firing at first increases and 

 then declines rapidly during the first second or two and reaches either a 

 constant steady state, as in the case for the response to NaCl in a good 

 and fresh rat preparation, or a slowly declining state. This initial incre- 

 ment is not as stable and reproducible as the steady state and is probably 

 a function of the properties of the nerve fiber rather than the taste cell 

 since it is not present in single taste cell recordings. The initial transient 

 response is not linearly related to the magnitude of the steady state 

 response that may follow, but it may be very important at low stimuli 

 concentrations. The rat threshold to NaCl may be as much as a hundred 

 or thousand times lower when the intial response rather than that of the 

 steady state, is used as a criterion of response. It should be noted that 

 when the electrical neural activity is integrated, the magnitude of the 



