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.
Confidence votes 11.7K. Almost all insect bites or stings leave welts, if they have the horsepower to break the skin. If it's not a chemical blend they inject to make feeding easier, their saliva can also cause a localised allergic reaction. The bite should be expected to increase for a few hours, and then decrease in size and effect in 1-2 days, although some stay longer.