axon reflex

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A reflex response to scratching of the skin with a sharp object: a red line appears within seconds, followed by a red flare in the surrounding skin, and finally a white weal, these phenomena constituting the triple response. The weal and flare result from the activity of pain receptors that transmit impulses along their axons not only in the normal orthodromic direction towards the central nervous system but also in the antidromic direction from axon forking nodes into the neighbouring skin, where the free nerve endings respond by releasing substance P, which binds to artery walls causing them to dilate and to produce the flare response, and which also binds to mast cells and stimulates them to release histamine, resulting in the accumulation of fluid that constitutes the weal response.

Subjects: Psychology.

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