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.
Cold urticaria (essentially meaning cold hives) is a disorder where hives or large red welts form on the skin after exposure to a cold stimulus. The welts are usually itchy and often the hands and feet will become itchy and swollen as well. Hives vary in size from about 7mm in diameter to as big as about 27mm diameter or larger.