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.
Acute hives often result from an allergy, but they can have many other causes. The medical term for hives is urticaria (ur-tih-CARE-ee-uh). When large welts occur deeper under the skin, the medical term is angioedema (an-gee-oh-eh-dee-ma). This can occur with hives, and often causes the eyelids and lips to swell.