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.
A common cause of hives or welts is an allergic reaction to a molecule found in substances such as food, pollen, poison ivy, soap, lotion, medicine or insect bite. When you are exposed to an allergen, your body responds to it by releasing chemicals, such as histamine. As a result, you can develop a skin rash.