E43 Thermoreceptors and thermal gradients

Topic

This same insect thermoreceptor enables the detection of a relevant temperature gradient, serving purposes such as the insect's behavioral thermoregulation, the localization of a host, or the detection of a fire.

Fourier heat diffusion—a process described in another model within this set—explains how changes in ambient temperature penetrate to the insect's internal sensory organ, thereby determining the organ's response speed.

The insect's transient receptor potential (TRP) channel is a specific transmembrane protein that opens in response to temperature; this activation occurs at a fixed temperature threshold—a mechanism also modeled elsewhere in this set regarding thermosensitive ion channels—with kinetics described by a Boltzmann distribution characterized by both a threshold temperature and a specific transition width.

*Melanophila acuminata* (the burnt-wood beetle) detects fires from a considerable distance using infrared sensors—specifically, pit organs—much like the pit vipers and infrared drones modeled elsewhere in this set, all of which absorb thermal radiation in accordance with the Stefan-Boltzmann law. As the fire draws closer to the beetle, the thermal radiation absorbed by the pit organ becomes increasingly intense. Consequently, in this model—which began by identifying a significant temperature gradient—the thermoreceptor's ultimate limiting sensitivity is determined by two factors: the signal-to-noise ratio established by another model in this set, and the biochemical thermal coefficient regarding metabolic rate established by yet another distinct model in the same set. A more favorable signal-to-noise ratio for the thermoreceptor results, in turn, in a higher ultimate limiting sensitivity for detecting the specific temperature gradient with which the model began.

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