Editing Thermoception

{{Short description|Sensation and perception of temperature}}
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In [[physiology]], '''thermoception''' or '''thermoreception''' is the [[Sense|sensation]] and [[perception]] of [[temperature]], or more accurately, temperature differences inferred from [[heat flux]]. It deals with a series of events and processes required for an organism to receive a temperature [[Stimulus (physiology)|stimulus]], convert it to a molecular signal, and recognize and characterize the signal in order to trigger an appropriate response. Thermal stimuli may be [[Noxious stimulus|noxious]] (posing a threat to the subject) or innocuous (no threat).<ref name="Tominaga">{{cite journal |last1=Tominaga |first1=Makoto |last2=Kashio |first2=Makiko |title=Thermosensation and TRP Channels |journal=Thermal Biology |date=2024 |volume=1461 |pages=3–13 |doi=10.1007/978-981-97-4584-5_1}}</ref> The temperature sensitive proteins in [[thermoreceptor]]s may also be activated by menthol or capsaicin, hence why these molecules evoke cooling and burning sensations, respectively.

A [[thermoreceptor]] may absorb heat via [[thermal conduction|conduction]], [[Convection (heat transfer)|convection]] or [[thermal radiation|radiation]]. However, the type of [[heat transfer]] is usually irrelevant to the functioning of a thermoceptor. [[Transient receptor potential channel]]s (TRP channels){{efn|name= trpChannels|The TRPV1 and TRPM8 receptors play key roles in the perception of heat and cold.<ref name="Nobel_2021a">{{cite web | work = The Nobel Assembly at Karolinska Institutet | url = https://www.nobelprize.org/prizes/medicine/2021/press-release/ | date = 4 October 2021 | title = Press release: The Nobel Prize in Physiology or Medicine 2021: David Julius, and Ardem Patapoutian }}</ref><ref name="Nobel_2021b" />}} are believed to play a role in many species in sensation of hot, cold, and pain.  [[Vertebrates]] have at least two types of thermoreceptors: those that detect heat and those that detect cold.<ref name=Johnson2008-p332-335>{{cite book | vauthors = Johnson JI | year = 2008 | chapter = 6.16 Specialized Somatosensory Systems, 6.16.2 Thermal Sensory Systems | veditors = Kaas JH, Gardner EP | title = The Senses: A Comprehensive Reference | volume = 6: Somatosensation | publisher = Elsevier | pages = 332–335 }}</ref>

==Heat transfer==
Thermoception depends on the [[heat transfer|transfer of heat]] from the environment to the thermoreceptor. The transfer may be [[thermal conduction|conductive]], [[Convection (heat transfer)|convective]] or [[thermal radiation|radiative]], but the method is irrelevant to the thermoceptor, which simply detects its own temperature, not that of the environment. The temperature of a thermoreceptor is the result of an [[First law of thermodynamics|energy balance]] between the heat flux from the environment and the heat dissipation to the rest of the body (or vice versa for cold detection). For example, a low-temperature metal, with high [[thermal conductivity]] may feel warmer than a high-temperature ceramic, with low thermal conductivity, because touching the metal results in a higher temperature of the thermoreceptor itself.

==Thermoreceptors==
{{main|thermoreceptor}}

A [[thermoreceptor]] is a non-specialised [[sense]] [[Cutaneous receptor|receptor]], or more accurately the receptive portion of a [[sensory neuron]], that detects absolute and relative changes in [[temperature]] In mammals, temperature receptors innervate various tissues including the skin (as [[Cutaneous receptor|cutaneous receptors]]), [[cornea]] and [[urinary bladder]]. In warm receptors, warming results in an increase in their action potential discharge rate, while cooling results in a decrease in discharge rate. In cold receptors, their firing rate increases during cooling and decreases during warming.

=== Molecular basis ===
[[File:Thermoreception 2.png|thumb|300px|Channels shown: [[TRPA1]], [[TRPM8]], [[TRPV4]], [[TRPV3]], [[TRPV1]], [[TRPM3]], [[ANO1]], [[TRPV2]]]]

This area of research has recently received considerable attention with the identification and cloning of the [[Transient Receptor Potential]] (TRP) family of proteins. A number of [[ion channels]] are responsible for thermoception and activate at various temperatures so are therefore responsible for different types of thermal stimuli. [[TRPV1]] is the primary channel associated with noxious heat sensing, as well as the detection of [[capsaicin]]. Innocuous warm sensation is mediated by activation of [[TRPM2]]. Innocuous cool sensation is mediated by activation of [[TRPM8]].<ref name="Tominaga"/> [[TRPA1]] is sometimes sensitive to [[menthol]] and considered to be related to noxious cool sensation, but the mechanism is unclear.<ref name="Tominaga"/>

The [[Nobel Prize in Physiology or Medicine]] in 2021 was attributed to [[David Julius]] (professor at the [[University of California, San Francisco]], USA) and [[Ardem Patapoutian]] (neuroscience professor at [[Scripps Research]] in [[La Jolla, California]], USA) "for their discovery of receptors for temperature and touch".<ref name="Nobel_2021a" /><ref name="Nobel_2021b">{{cite web|url=https://www.nobelprize.org/uploads/2021/10/press-medicineprize2021.pdf|title=The Nobel Prize in Physiology or Medicine|publisher=Nobel Foundation|access-date=2021-10-04}}</ref>

==In humans==
In humans, temperature sensation from [[thermoreceptor]]s{{efn|name= trpChannels}} enters the spinal cord along the axons of [[Lissauer's tract]] that synapse on second order neurons in [[grey matter]] of the [[Posterior horn of spinal cord|dorsal horn]]. The axons of these second order neurons then [[decussation|decussate]], joining the [[spinothalamic tract]] as they ascend to neurons in the [[ventral posterolateral nucleus]] of the [[thalamus]].
A study in 2017 shows that the thermosensory information passes to the [[Parabrachial nuclei|lateral parabrachial nucleus]] rather than to the thalamus and this drives thermoregulatory behaviour.<ref name="Nakamura">{{cite journal | vauthors = Nakamura K | title = [Thermoregulatory behavior and its central circuit mechanism-What thermosensory pathway drives it?] | journal = Clinical Calcium | volume = 28 | issue = 1 | pages = 65–72 | date = 2018 | pmid = 29279428 }}</ref><ref name="Yahiro">{{cite journal | vauthors = Yahiro T, Kataoka N, Nakamura Y, Nakamura K | title = The lateral parabrachial nucleus, but not the thalamus, mediates thermosensory pathways for behavioural thermoregulation | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 5031 | date = July 2017 | pmid = 28694517 | pmc = 5503995 | doi = 10.1038/s41598-017-05327-8 | bibcode = 2017NatSR...7.5031Y }}</ref>

==Thermal vision==
[[File:Pit organs of a python.jpg|thumb|Positions of the pit organs (arrowed in red) on a python, relative to its nostril (black arrow)]]
Thermal vision is the ability to detect heat through radiative means. [[Visual perception|Vision]] specifically denotes the ability to not only detect heat but also form an image with that information. However, given the lack of knowledge or uncertainty of how an organism may interpret their thermoreceptor signals, any organism with organs specifically evolved for radiative thermoception are generally classed as thermal vision.

=== In snakes ===
{{main|Infrared sensing in snakes}}
[[Crotalinae]] (pit viper) and [[Boidae]] (boa) snakes can effectively see the infrared radiation emitted by hot objects.<ref>{{cite journal | vauthors = Newman EA, Hartline PH | title = The infrared "vision" of snakes | journal = Scientific American | date = March 1982 | volume = 246 | issue = 3 | pages = 116–127 | doi = 10.1038/scientificamerican0382-116 | jstor = 24966551 | bibcode = 1982SciAm.246c.116N }}</ref> The snakes' face has a pair of holes, or pits, lined with temperature sensors.  The sensors indirectly detect infrared radiation by its heating effect on the skin inside the pit. They can work out which part of the pit is hottest, and therefore the direction of the heat source, which could be a warm-blooded prey animal. By combining information from both pits, the snake can also estimate the distance of the object.

=== In vampire bats ===
{{main|Infrared sensing in vampire bats}}
The [[Common vampire bat]] has specialized infrared sensors in its nose-leaf.<ref name="Kürten_1984">{{cite journal | vauthors = Kürten L, Schmidt U, Schäfer K | title = Warm and cold receptors in the nose of the vampire bat Desmodus rotundus | journal = Die Naturwissenschaften | volume = 71 | issue = 6 | pages = 327–328 | date = June 1984 | pmid = 6472483 | doi = 10.1007/BF00396621 | bibcode = 1984NW.....71..327K }}</ref><ref name="Gracheva_2011">{{cite journal | vauthors = Gracheva EO, Cordero-Morales JF, González-Carcacía JA, Ingolia NT, Manno C, Aranguren CI, Weissman JS, Julius D | title = Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats | journal = Nature | volume = 476 | issue = 7358 | pages = 88–91 | date = August 2011 | pmid = 21814281 | pmc = 3535012 | doi = 10.1038/nature10245 }}</ref> Vampire bats are the only mammals that feed exclusively on blood. The infrared sense enables Desmodus to localize homeothermic (warm-blooded) animals ([[cattle]], [[horses]], wild mammals) within a range of about 10 to 15&nbsp;cm. This [[Infrared sensing in vampire bats|infrared perception]] is possibly used in detecting regions of maximal blood flow on targeted prey.

===In other mammals===
Dogs, like vampire bats, can detect weak thermal radiation with their [[rhinaria]] (noses).<ref name="Bálint_2020">{{cite journal | vauthors = Bálint A, Andics A, Gácsi M, Gábor A, Czeibert K, Luce CM, Miklósi Á, Kröger RH | title = Dogs can sense weak thermal radiation | journal = Scientific Reports | volume = 10 | issue = 1 | pages = 3736 | date = February 2020 | pmid = 32111902 | pmc = 7048925 | doi = 10.1038/s41598-020-60439-y | bibcode = 2020NatSR..10.3736B }}</ref>

On February 14, 2013 researchers developed a [[neural implant]] that gives [[rat]]s the ability to sense [[infrared]] light which for the first time provides [[living creatures]] with new abilities, instead of simply replacing or augmenting existing abilities.<ref>{{cite magazine|url=https://www.wired.co.uk/news/archive/2013-02/14/implant-gives-rats-sixth-sense-for-infrared-light|title=Implant gives rats sixth sense for infrared light|magazine=Wired UK|date=14 February 2013|access-date=14 February 2013|archive-date=17 February 2013|archive-url=https://web.archive.org/web/20130217055046/http://www.wired.co.uk/news/archive/2013-02/14/implant-gives-rats-sixth-sense-for-infrared-light|url-status=dead}}</ref>

=== In invertebrates ===
Other animals with specialized heat detectors are forest fire seeking beetles (''[[Melanophila acuminata]]''), which lay their eggs in [[conifers]] freshly killed by forest fires. Darkly pigmented butterflies ''[[Pachliopta aristolochiae]]'' and ''[[Troides rhadamantus]]'' use specialized heat detectors to avoid damage while basking. The blood sucking [[Hemiptera|bugs]] ''[[Triatoma infestans]]'' may also have a specialised thermoception organ.


== See also ==
* [[Infrared sensing in snakes]]
* [[Infrared sensing in vampire bats]]
* [[List of Nobel laureates in Physiology or Medicine#Laureates]]
* {{Annotated link|Electroreception}}
* {{Annotated link|Mechanoreceptor}}
* {{Annotated link|Nociception}}
* {{Annotated link|Proprioception}}
* [[Thermoregulation]]

==Notes==
{{Notelist|33em}}

== References ==
{{Reflist|30em}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Campbell AL, Naik RR, Sowards L, Stone MO | title = Biological infrared imaging and sensing | journal = Micron | volume = 33 | issue = 2 | pages = 211–25 | date = 2002 | pmid = 11567889 | doi = 10.1016/s0968-4328(01)00010-5 | url = https://zenodo.org/record/1260182 }}
{{refend}}

{{Sensation and perception|state=collapsed}}
{{Authority control}}

[[Category:Perception]]
[[Category:Sensory systems]]
[[Category:Temperature]]