Neruonal signaling is not dissimilar to hormonal signaling in that it involves the release of a signaling molecule, in this case a neurotransmitter, that acts on a target cell. The target cell has a receptor at the synapse for transmitter uptake. Because the transmitter needs to work locally at a synapse and at a very fast rate, it is released in higher concentrations than most endocrine hormones. Paracrine signaling involves signaling between adjacent cells rather than between cells of one tissue acting on target tissues at great distances, as is the case in hormonal signaling. Hormonal signaling takes place between different tissues, often between different organs, at great distances.
Hormones act is small quantities and are usually carried in the serum.
B. Without being too rigid, there are basically three mechanisms by which hormones signal. The classic are the sex hormones, most of which are based on cholesterol. These modulate the activity of allosteric enzymes at the metabolic level. In this case the hormone receptors are either themselves enzymes capable of protein phosphorylation or directly associated with such protein kinases. The action of these hormones is so complex that their means of signaling are only now being worked out.