<unk>  <unk>  is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of<unk> etic<unk> id and choline. Parts in the body that use or are affected by<unk>  are referred to as cholinergic. Substances that increase or decrease the overall<unk> tivity of the cholinergic system are called cholinergics and anticholinergics, respectively.<unk>  is the neurotransmitter used at the neuromuscular junction—in other words, it is the chemical that motor neurons of the nervous system release in order to<unk> tivate muscles. This property means that drugs that affect cholinergic systems can have very dangerous effects ranging from paralysis to convulsions.<unk>  is also a neurotransmitter in the autonomic nervous system, both as an internal transmitter for the sympathetic nervous system and as the final product released by the parasympathetic nervous system.<unk>  is the primary neurotransmitter of the parasympathetic nervous system. In the brain,<unk>  functions as a neurotransmitter and as a neuromodulator. The brain contains a number of cholinergic areas, each with distinct functions; such as playing an important role in arousal, attention, memory and motivation.<unk>  has also been traced in cells of non-neural origins and microbes. Recently, enzymes related to its synthesis, degradation and cellular uptake have been traced back to early origins of unicellular eukaryotes. The protist pathogen<unk> anthamoeba spp. has shown the presence of<unk> , which provides growth and proliferative signals via a membrane located M1-muscarinic receptor homolog. Partly because of its muscle-activating function, but also because of its functions in the autonomic nervous system and brain, many important drugs exert their effects by altering cholinergic transmission. Numerous venoms and toxins produced by plants, animals, and bacteria, as well as chemical nerve agents such as Sarin, cause harm by inactivating or hyperactivating muscles through their influences on the neuromuscular junction. Drugs that<unk> t on muscarinic<unk>  receptors, such as atropine, can be poisonous in large quantities, but in smaller doses they are commonly used to treat certain heart conditions and eye problems. Scopolamine, which<unk> ts mainly on muscarinic receptors in the brain, can cause delirium, hallucinations, and amnesia. The addictive qualities of nicotine are derived from its effects on nicotinic<unk>  receptors in the brain.
Acetylcholine
Serotonin
N-Acetylserotonin
Neuropil
Beta-Endorphin
Opioid peptide
Gluten exorphin
Glutamate 