"Itching arises with local inflammation from an insect bite, allergy, or other irritant. Itch sensations travel along small-diameter, slow neurons to the spinal cord and thence to the brain via the spinothalamic pathway [13]. Any patch of skin that itches also has mechanoreceptors that detect touch and vibration, whose signals make their way to the spinal cord via fast, large-diameter neurons that spinal neurons relay to the brain via a pathway called the dorsal columns [13]."
"Within the spinal cord, slow/itch and fast/touch sensory neurons from the skin synapse on interneurons that cross-connect the two pathways: mechanoreceptors for touch and vibration activate neurons that inhibit signals from the itch pathway, and "itch" receptors inhibit those same inhibitory neurons [1-4]. Thus, an unscratched (no mechanoreceptor input) itch travels unimpeded from your skin to your brain, knocking down anti-itch activity in the spinal cord."
Itch arises from local inflammation such as insect bites or allergies and travels via small-diameter, slow neurons to the spinal cord and brain through the spinothalamic pathway. Skin mechanoreceptors for touch and vibration send signals faster through large-diameter neurons via the dorsal columns. In the spinal cord, interneurons cross-connect itch and touch pathways so mechanoreceptor activation inhibits itch signals while itch receptors suppress those inhibitory neurons. Scratching activates mechanoreceptors, increasing inhibition of itch signals and reducing unpleasant sensations. Touch also "gates off" pain, activates descending inhibitory pathways from the brain, and engages brain reward centers when skin is touched.
Read at Psychology Today
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