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.
Underlying causes of WWI (M.A.I.N.) Nationalism was both uniting and dividing Europe. Imperialism was the cause of increased competition among European countries for colonies in Asia and Africa. Alliances: two armed camps existed in Europe on the eve of WWI. Militarism was encouraged because of the increased distrust of the other side.