Sensory receptor
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222713214
2008-06-30T19:19:04Z
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/* Structure */
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In a [[sensory system]], a '''sensory receptor''' is a structure that recognizes a [[stimulus (physiology)|stimulus]] in the internal or external environment of an [[organism]]. In response to stimuli the sensory receptor initiates [[sensory transduction]] by creating [[graded potential]]s or [[action potential]]s in the same cell or in an adjacent one.
==Functions==
The [[sensory receptor]]s involved in taste and smell contain [[receptor (biochemistry)|receptors]] that bind to specific chemicals. [[Odor receptor]]s in [[olfactory receptor neuron]]s, for example, are activated by interacting with molecular structures on the [[odor]] molecule. Similarly, [[taste]] receptors (gustatory receptors) in [[taste bud]]s interact with chemicals in food to produce an [[action potential]].
Other receptors such as [[mechanoreceptor]]s and [[photoreceptor]]s respond to physical stimuli. For example, [[photoreceptor cell]]s contain specialized proteins such as [[rhodopsin]] to [[transduction (physiology)|transduce]] the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.
The sensory receptor functions as the first component in a sensory system.
Sensory receptors respond to specific stimulus modalities. The stimulus modality to which a sensory receptor responds is determined by the sensory receptor's [[adequate stimulus]].
The sensory receptor responds to its stimulus modality by initiating sensory transduction. This may be accomplished by a net shift in the initial states of a receptor(see a picture of these putative states [http://www.bio-balance.com/Receptor2.htm] with the biophysical description - link [http://www.bio-balance.com/Graphics.htm]).
==Classification==
===by adequate stimulus===
A sensory receptor's adequate stimulus is the stimulus modality for which it possesses the adequate [[sensory transduction]] apparatus. Adequate stimulus can be used to classify sensory receptors:
*[[Ampullae of Lorenzini]] respond to [[electric fields]], salinity, and to temperature, but function primarily as electroreceptors
*[[Baroreceptor]]s respond to pressure
*[[Chemoreceptor]]s respond to chemical stimuli
*[[Hydroreceptor]]s respond to changes in humidity
*[[Mechanoreceptor]]s respond to [[mechanical stress]] or [[mechanical strain]]
*[[Nociceptor]]s respond to damage to body tissues leading to pain perception
*[[Osmoreceptor]]s respond to the [[osmolarity]] of fluids (such as in the hypothalamus)
*[[Photoreceptor]]s respond to light
*[[Proprioceptor]]s provide the sense of position
*[[Thermoreceptor]]s respond to temperature, either heat, cold or both
===by location===
Sensory receptors can be classified by location:
*[[Cutaneous receptor]]s are sensory receptors found in the dermis or epidermis.
*[[Muscle spindle]]s contain mechanoreceptors that detect stretch in muscles.
===by morphology===
Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology:
*[[Free nerve endings]] characterize the [[nociceptor]]s and [[thermoreceptor]]s and are called thus because the terminal branches of the neuron are unmyelinated and spread throughout the [[dermis]] and [[Epidermis (skin)|epidermis]].
*[[Encapsulated receptor]]s consist of the remaining types of cutaneous receptors. Encapsulation exists for specialized functioning.
==Innervation==
{{Main|Sensory fiber types}}
Different sensory receptors are innervated by different types of [[nerve fibers]]. Muscles and associated sensory receptors are innvervated by type I and II sensory fibers, while [[cutaneous receptors]] are innervated by Aβ, Aδ and C fibers.
==See also==
*[[Sense]]
*[[Sensory neuron]]
*[[Proprioception]]
*[[Receptor theory]]
==External links==
* {{MeshName|Sensory+Receptors}}
{{Sensory_system}}
[[Category:Sensory receptors]]
[[id:Reseptor indra]]
[[bg:Рецептор]]
[[es:Receptor sensorial]]
[[fr:Récepteur sensoriel]]
[[he:קולטן תחושתי]]
[[it:Recettore sensoriale]]
[[hu:Receptor]]
[[mk:Рецептор]]
[[sl:Čutilni receptor]]
[[sr:Чулна ћелија]]
[[zh:感受器]]