There is a difference in the lengths of the neurons for each subdivision, however, helping to separate these two divisions on an anatomic basis. The parasympathetic preganglionic neurons exit the spinal cord both from the cervical and sacral spinal cord. The sympathetic preganglionic neurons exit the spinal cord from the thoracic spinal cord and from the upper lumbar spinal cord. Generally, the two divisions of the ANS usually have opposite effects on the organ that they innervate. Muscarinic cholinergic receptors are so named because they are stimualted by muscarine, a toxin isolated from a certain species of mushroom, as well as acetylcholine of course.
Adrenergic receptors exists as slightly different molecular subvariants.
There are alpha adrenergic and beta adrenergic receptors. Both types are stimualted by adrenalin, but because of the slight differences, synthetic as well as naturally occurring substances can stimulate alpha, but not beta receptors. Knowledge of ANS receptor types and subtypes that exist in tissues of organs is very useful pharmacologically. The heart and lung bronchiole airways contain mostly beta adrenergic receptors, whereas arteriole blood vessels contain primarily alpha adrenergic receptors. Blood vessel diameter can thus be constricted using an alpha adrenergic substance, without significant stimulation fo the heart of lungs.