A<unk>  receptor<unk>  (MRA) is a type of anticholinergic agent that blocks the activity of the<unk>  acetylcholine receptor. The<unk>  receptor is a protein involved in the transmission of signals through certain parts of the nervous system, and<unk>  receptor<unk> s work to prevent this transmission from occurring. Notably,<unk> s reduce the activation of the parasympathetic nervous system. The normal function of the parasympathetic system is often summarised as "rest-and-digest", and includes slowing of the heart, an increased rate of digestion, narrowing of the airways, promotion of urination, and sexual arousal.<unk> s counter this parasympathetic "rest-and-digest" response, and also work elsewhere in both the central and peripheral nervous systems. Drugs with<unk>  activity are widely used in medicine, in the treatment of low heart rate, overactive bladder, respiratory problems such as asthma and COPD, and neurological problems such as Parkinson's disease and Alzheimer's disease. A number of other drugs, such as antipsychotics and the tricyclic family of antidepressants, have incidental<unk>  activity which can cause unwanted side effects such as difficulty urinating, dry mouth and skin, and constipation. Acetylcholine (often abbreviated ACh) is a neurotransmitter whose receptors are proteins found in synapses and other cell membranes. Besides responding to their primary neurochemical, neurotransmitter receptors can be sensitive to a variety of other molecules. Acetylcholine receptors are classified into two groups based on this: *<unk> , which respond to muscarine * nicotinic, which respond to nicotine Most<unk>  receptor<unk> s are synthetic chemicals; however, the two most commonly used anticholinergics, scopolamine and atropine, are belladonna alkaloids, and are naturally extracted from plants such as Atropa belladonna, the deadly nightshade. The name "belladonna", Italian for "beautiful lady", is thought to derive from one of the antimuscarinic effects of these alkaloids: they were used by women for cosmetic purposes, to promote dilation of the pupils.<unk>  effects and<unk>  agonist effects counterbalance each other for homeostasis. Certain<unk> s can be classified into either long-acting<unk>  receptor<unk> s (LAMAs) or short-acting<unk>  receptor<unk> s (SAMAs), depending on when maximum effect occurs and for how long the effect persists.
Muscarinic antagonist
Alpha-adrenergic agonist
Beta-adrenergic agonist
Adenosine receptor antagonist
Dopamine agonist
Beta2-adrenergic agonist
Norepinephrine–dopamine disinhibitor
Dopamine antagonist