Acetylcholine is released from a presynaptic neuron into the synaptic cleft. Once in the synaptic gap, acetylcholine can: - Bind to presynaptic receptors: presynaptic activation or inhibition leads to automodulation of the presynaptic cholinergic neuron.
When welts are a sign of a medical problem, they are usually accompanied by other symptoms which provide clues to the problem. Physical trauma such as a blow can cause a welt, and welts can also be caused by allergic reactions, infections, injections, insect bites, and skin reactions, in very sensitive people. For example, in people with dermographism, even a gentle touch to the skin can cause a welt to emerge.
1 Cold Urticaria-Also known as hives. 2  A release of histamine during re-warming after a period of cooling, causing red, itchy welts on the skin. 3  Cold Erythema-A rash, characterised by redness and itching, caused by exposure to cold. 4  Can cause severe pain and muscular spasms.