- Sensory receptor
In a
sensory system , a sensory receptor is a structure that recognizes a stimulus in the internal or external environment of anorganism . In response to stimuli the sensory receptor initiatessensory transduction by creatinggraded potential s oraction potential s in the same cell or in an adjacent one.Functions
The
sensory receptor s involved in taste and smell contain receptors that bind to specific chemicals.Odor receptor s inolfactory receptor neuron s, for example, are activated by interacting with molecular structures on theodor molecule. Similarly,taste receptors (gustatory receptors) intaste bud s interact with chemicals in food to produce anaction potential .Other receptors such as
mechanoreceptor s andphotoreceptor s respond to physical stimuli. For example,photoreceptor cell s contain specialized proteins such asrhodopsin to 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 toelectric 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 tomechanical stress ormechanical strain
*Nociceptor s respond to damage to body tissues leading to pain perception
*Osmoreceptor s respond to theosmolarity 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 bothby 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 thenociceptor s andthermoreceptor s and are called thus because the terminal branches of the neuron are unmyelinated and spread throughout thedermis and epidermis.
*Encapsulated receptor s consist of the remaining types of cutaneous receptors. Encapsulation exists for specialized functioning.Innervation
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, whilecutaneous receptors are innervated by Aβ, Aδ and C fibers.ee also
*
Sense
*Sensory neuron
*Proprioception
*Receptor theory External links
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