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.
Reactions to the bites may be delayed. In fact, in some cases it can be a day or more before the welts appear. Once they appear, the welts shrink down to red spots, but those spots can last for days. It is estimated that around 30% of people do not have a reaction to bed bug bites. No itching, no swelling, nada.