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.
These itchy welts can show up anywhere on your skin. Theyâre caused by an allergic or other type of reaction. Your doctor may call them urticaria. They can last a few minutes or several days before they go away. Sometimes theyâre a sign of more serious problems, especially when you have trouble breathing. Hives that recur or that last more than 6 weeks are considered chronic urticaria and require further evaluation.