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.
About 20% of people get hives -- itchy red or skin-colored welts also known as urticaria. Theyâre often caused by an allergic reaction to a food or drug. Usually, they go away quickly. For a small number of people, though, hives come back again and again, with no known cause. When new outbreaks happen almost every day for 6 weeks or more, itâs called chronic idiopathic urticaria (CIU). One percent or less of people have it. Itâs most common in people between the ages of 20 and 40.