What is the difference between Labeled Line theory Cross Fiber theory and Between Fiber theory of taste?

Answer 1

Labeled line theory assumes a taste receptor cell (TRC) is specifically "tuned" for a specific tastant or taste modality. for example, one TRC will respond to sweet more strongly than others while a neighboring TRC will respond better to bitter. This response is then sent through afferent nerves that are also specifically tuned to that response. in the most simple terms, a TRC specific to sweet, responds only to sweet, and sends its neuronal signal down a spefic afferent nerve that translates the "sweet" message to the ganglion cell.

In cross fiber theory, the TRC still may be tuned to a specific taste modality, such as sweet, but the afferent nerve fibers are not specific. meaning, that although the TRCs are specific and discriminating, the nerve fibers will Cary more than one signal. so a bitter and sweet TRC can send signals down the same fiber. this then requires deduction of a particular pattern of several afferent nerves to determine the tastant. in the labeled line theory, everything remains in a straight line and the code is easy to determine because specific cells and specific nerve fibers Cary specific tastant responses.

Additionally, the TRC's may respond to several types of stimuli and send the signal through afferent nerves that Cary several signals. this is the most complicated of the models, in that, it does not have any selectivity. You can imagine one TRC that will respond to any taste. this signal is sent through an afferent nerve that is carying several other signals from other TRCs. this particular model requires the largest amount of decoding of the neuronal signal.