There is a difference in the lengths of theneurons for each subdivision, however, helping to separate these two divisionson an anatomic basis. The parasympathetic preganglionic neurons exit the spinalcord both from the cervical and sacral spinal cord. The sympatheticpreganglionic neurons exit the spinal cord from the thoracic spinal cord andfrom the upper lumbar spinal cord. Generally, the two divisions of the ANSusually have opposite effects on the organ that they innervate. Muscarinic cholinergic receptorsare so named because they are stimualted by muscarine, a toxin isolated from acertain species of mushroom, as well as acetylcholine of course.
Adrenergic receptors exists as slightlydifferent molecular subvariants.
There are alpha adrenergic and beta adrenergicreceptors. Both types are stimualted by adrenalin, but because of the slightdifferences, synthetic as well as naturally occurring substances can stimulatealpha, but not beta receptors. Knowledge of ANS receptor types and subtypesthat exist in tissues of organs is very useful pharmacologically. The heart andlung bronchiole airways contain mostly beta adrenergic receptors, whereasarteriole blood vessels contain primarily alpha adrenergic receptors. Bloodvessel diameter can thus be constricted using an alpha adrenergic substance,without significant stimulation fo the heart of lungs.