These messages were travelling down A-delta fibres, which are large, and coated in insulating myelin, meaning their signals travel rapidly. They detect mechanical damage over a certain threshold (and possibly heat damage as well in some cases) and the pain they produce is described as sharp, stinging or pricking. It is also easy to localise. You know almost immediately exactly where that drawing pin you stepped on has embedded itself in your foot! But as she sat there, with the cuff blocking the blood flow, her arm began to go numb. The large A-delta fibres, which need a lot of energy, were
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