World Library  
Flag as Inappropriate
Email this Article

Thermoreceptor

Article Id: WHEBN0000569842
Reproduction Date:

Title: Thermoreceptor  
Author: World Heritage Encyclopedia
Language: English
Subject: Cutaneous receptor, Sensory system, Somatosensory system, Sensory receptor, Mechanoreceptor
Collection: Sensory Receptors
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Thermoreceptor

A thermoreceptor is a infrared part of the spectrum.

In humans, temperature sensation enters the spinal cord along the axons of Lissauer's tract that synapse on second order neurons in grey matter of the dorsal horn, one or two vertebral levels up. The axons of these second order neurons then decussate, joining the spinothalamic tract as they ascend to neurons in the ventral posterolateral nucleus of the thalamus.

Contents

  • Location 1
  • Structure 2
  • Function 3
  • Distribution 4
  • Mechanism of transduction 5
  • References 6

Location

In mammals, temperature receptors innervate various tissues including the skin (as cutaneous receptors), cornea and urinary bladder. Neurons from the pre-optic and hypothalamic regions of the brain that respond to small changes in temperature have also been described, providing information on core temperature. The hypothalamus is involved in thermoregulation, the thermoreceptors allowing feed-forward responses to a predicted change in core body temperature in response to changing environmental conditions.

Structure

Thermoreceptors have been classically described as having 'free' non-specialised endings; the mechanism of activation in response to temperature changes is not completely understood.

Function

Cold-sensitive thermoreceptors give rise to the sensations of cooling, cold and freshness. In the cornea cold receptors are thought to respond with an increase in firing rate to cooling produced by evaporation of lacrimal fluid 'tears' and thereby to elicit a reflex blink.

Distribution

Warm and cold receptors play a part in sensing innocuous environmental temperature. Temperatures likely to damage an organism are sensed by sub-categories of nociceptors that may respond to noxious cold, noxious heat or more than one noxious stimulus modality (i.e., they are polymodal). The nerve endings of sensory neurons that respond preferentially to cooling are found in moderate density in the skin but also occur in relatively high spatial density in the cornea, tongue, bladder, and facial skin. The speculation is that lingual cold receptors deliver information that modulates the sense of taste; i.e. some foods taste good when cold, while others do not.

Mechanism of transduction

This area of research has recently received considerable attention with the identification and cloning of the Transient Receptor Potential (TRP) family of proteins. The transduction of temperature in cold receptors is mediated in part by the TRPM8 channel. This channel passes a mixed inward cationic (predominantly carried by Na+ ions although the channel is also permeable to Ca2+) current of a magnitude that is inversely proportional to temperature. The channel is sensitive over a temperature range spanning about 10-35°C. TRPM8 can also be activated by the binding of an extracellular ligand. Menthol can activate the TRPM8 channel in this way. Since the TRPM8 is expressed in neurons whose physiological role is to signal cooling, menthol applied to various bodily surfaces evokes a sensation of cooling. The feeling of freshness associated with the activation of cold receptors by menthol, particularly those in facial areas with axons in the trigeminal (V) nerve, accounts for its use in numerous toiletries including toothpaste, shaving lotions, facial creams and the like.

Another molecular component of cold transduction is the temperature dependence of so-called leak channels which pass an outward current carried by potassium ions. Some leak channels derive from the family of two-pore (2P) domain potassium channels. Amongst the various members of the 2P-domain channels, some close quite promptly at temperatures less than about 28°C (e.g. TRAAK, TREK). Temperature also modulates the activity of the Na+/K+-ATPase. The Na+/K+-ATPase is a P-type pump that extrudes 3Na+ ions in exchange for 2K+ ions for each hydrolytic cleavage of ATP. This results in a net movement of positive charge out of the cell, i.e. a hyperpolarizing current. The magnitude of this current is proportional to the rate of pump activity.

It has been suggested that it is the constellation of various thermally sensitive proteins together in a neuron that gives rise to a cold receptor.[2] This emergent property of the neuron is thought to comprise, the expression of the aforementioned proteins as well as various voltage-sensitive channels including the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channel and the rapidly activating and inactivating transient potassium channel (IKA).

References

  1. ^ Darian-Smith, Ian; Johnson KO; LaMotte C; Shigenaga Y; Kenins P; Champness P (1979). "Warm fibers innervating palmar and digital skin of the monkey: responses to thermal stimuli.". Journal of Neurophysiology 42 (5): 1297–1315.  
  2. ^ Viana, Felix; la Peña E; Belmonte C (2002). "Specificity of cold thermotransduction is determined by differential ionic channel expression.". Nature Neuroscience 5 (3): 254–260.  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.