The perception of harmful stimuli (termed nociception from Sherrington's terms 'nociceptive' and 'nociceptor') is closely related to, but distinct from, the sensation of pain. Polymodal nociceptors (PMNs) are peripheral sensory neurons that respond to noxious (i.e. potentially tissue-damaging) stimuli. They are mainly non-myelinated C fibres whose endings respond to intense thermal, mechanical and chemical stimuli (and hence are 'polymodal'). PMN fibres terminate in the dorsal horn of the spinal cord, forming synaptic connections with transmission neurons running to the thalamus. Chemical stimuli acting on PMNs include bradykinin, protons, ATP and vanil-loids (e.g. capsaicin, the component of chilli peppers responsible for their fiery flavour). PMNs are sensitized by prostaglandins, which explains the analgesic effect of anti-inflammatory drugs, particularly in the presence of inflammation.The transient receptor potential vanilloid receptor 1 (TRPV1) receptor responds to noxious heat as well as capsaicin-like agonists.
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