Polymodal nociceptors

These are a subset of sensory neurons having their cell bodies (small to medium size) in dorsal root and in cranial nerve ganglia and possessing nonmyelinated (C-type) or thinly myelinated (A-delta type) fibres. This subset of neurons express transient receptor potential vanilloid type 1 (TRPV1, or vanilloid, or capsaicin receptor) that is excited by capsaicin, the pungent ingredient of chilli. These neurons have been classified as polymodal nociceptors because they can be excited by various noxious stimuli. 

Nociceptors are a specific subset of peripheral sensory organs, which respond to noxious stimuli. A8 mechan-oreceptors and C-polymodal nociceptors are the two main classes of cutaneous nociceptors. The sensory quality of pain evoked by activation of A8-fibres is... 

Thermal nociceptors and mechanical nociceptors are associated with A-delta fibers. These are small myelinated fibers that transmit impulses at a rate of 5 to 30 m/sec. Polymodal nociceptors are associated with C fibers. These are small unmyelinated fibers that transmit impulses at a rate generally less than 1.0 m/sec (range of 0.5 to 2.0 m/sec). 

The lactic acid and other noxious chemicals stimulate polymodal nociceptors. 

Muscle spasm. The pain induced by muscle spasm results partially from the direct effect of tissue distortion on mechanical nociceptors. Muscle spasm also causes tissue ischemia. The increased muscle tension compresses blood vessels and decreases blood flow. Furthermore, the increased rate of metabolism associated with the spasm exacerbates the ischemia. As discussed earlier, ischemia leads to stimulation of polymodal nociceptors. 

The term nociceptor refers to sensory receptors that respond to noxious stimuli (see Kruger et al. 2003 for review). A variety of cutaneous primary afferent nociceptors have been described, primary among them are the unmyelinated C fibers that are characterized by free nerve endings. The C-polymodal nociceptor responds to... 

Konietzny, F. and Hensel, H., The effect of capsaicin on the response characteristics of hnman c-polymodal nociceptors, J. Therm. Biol, 8,213, 1983. 

The capacity of prostaglandins to sensitiie pain receptors to mechanical cmd chemical stimulation apparently results from a lowering of the threshold of the polymodal nociceptors of C fibers. 

A number of receptors (nociceptors) located on vagal afferent sensory airway nerves are responsive to a variety of noxious stimuli (chemical and mechanical) known to induce cough. In particular, the rapidly adapting receptor present on myelinated A5-type nerves, which appears polymodal (responding to both chemical and mechanical stimuli) and the small umnyelinated C-libres, sensitive to the chemical capsaicin, the tussive extract from hot chilli peppers, are widely believed to... 

SzolcsAnyi,/., 19806, Role of polymodal nociceptors in mediation of chemogenic pain and inflammatory hyperalgesia, Proc. Int. Physiol. Soc. 14 734. 

Treede RD, Magerl W. Modern concepts of pain and hyperalgesia beyond the polymodal C-nociceptor. News Physiol Sci 1995 10 216-228. 

Capsaican is a TRPV-1 agonist. TRPVl (also termed the capsaican receptor) is a polymodal nociceptor exhibiting a dynamic threshold of activation that is markedly reduced in inflammatory conditions [3]. TRPVl knock-out mice are devoid of post-inflammatory thermal hyperalgesia. TRPV receptors are in abundance on unmyelinated C fiber peripheral endings and respond to a variety of noxious mediators. Once activated these fibers transmit localized and... 

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