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.
White patches that develop on many areas of one's skin are usually caused by vitiligo. Causes: Vitiligo is a condition characterized by the loss of skin pigment called melanin, which is normally produced by cells called melanocytes. Discoloration is caused by the destruction of the melanocytes, but the exact cause is not known.