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.
Autoimmune Diseases and Allergies. Autoimmune diseases, such as lupus erythematosus and dermatomyositis, can also cause changes in skin color. Eczema is a type of hypersensitivity reaction (allergy) that can cause red, scaly patches that ooze.Related to eczema, pityriasis alba can cause dry, white patches on the skin in children.A wide variety of rashes, such as dermatitis herpetiformis, contact dermatitis, poison ivy rashes, and others can be caused by an allergic reaction.ou may have applied sunscreen in an incomplete manner, leading to differently tanned parts of your skin. Medications can make your skin more sensitive to the sun and more likely to turn red or burn. Radiation therapy may also cause a kind of burn and change the color of your skin.