The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with control and integration of visceral functions necessary for life such as cardiac output, blood flow distribution, and digestion.
I am also going to assume that will include things like breathing, sleeping cycles (and the processes that are involved with it)
EC50
1/2 of maximal effect concentration
The best-characterized drug receptors are regulatory proteins, which mediate the actions of endogenous chemical signals such as neurotransmitters, autacoids, and hormones.
Regulation of various key functions such as growth, metabolism, or even cell mediated death (apoptosis)
Still other drugs bind to a different site on the receptor than that bound by endogenous ligands; such drugs can produce useful and quite different clinical effects by acting as so-called allosteric modulators of the receptor.
Perhaps they bind in a way such that they alter the conformation of their binding partner that could either decrease or increase the targets' affinity for its natural ligand
Accordingly, changes in the chemical structure of a drug can dramatically increase or decrease a new drug’s affinities for different classes of receptors, with resulting alterations in therapeutic and toxic effects.
The development of new drugs from pre-existing compounds is often how we go about discovering new compunds that have better affinity or therapeutic effects.
For example, penicillin has the beta-lactam core component allowing it to interfere with bacterial membranes. The retention of that general structure and building off of it generates novel antibiotics like amoxicillin, ampicillin, Hetacillin and many more derivative forms.