Originally called ‘vagusschtuff’ by the physiologist Oscar Loewi (1873-1961), and first discovered by him in the vagus nerve of the frog heart, it is a white crystalline derivative of choline. As such, it is hormone-like, neurotransmitter protein, produced by cells to create or stimulate central nervous system reactions necessary for life. While being an important neurotransmitter in the central nervous system, it is also the main messenger for motoneurons in the peripheral nervous system, including the autonomic nervous system, and for cholinergic effector synapses. It is a ‘clever’ transmitter in that it functions to activate skeletal muscles and to inhibit cardiac muscle. Stored in synaptic vesicles, it is released in a quantal manner in response to calcium ion uptake when an action potential arrives. It diffuses across the synaptic cleft to transmit the nerve impulse across the synapse, and binds to receptor sites on the postsynaptic membrane, after which the ion channels open allowing positive ions to enter the cell that then triggers membrane depolarisation. Stimulated by nicotine, and depleted in Parkinson’s disease, it has been suggested that smoking tobacco may delay or even prevent the onset of the disease through the actions of nicotine on the basal ganglia (specifically the mesolimbic dopamine system).
See Acetylcholinesterase (AcHE), Action potential, α-bungarotoxin ((α-BTX), Basal ganglia (disorders), Cholinergic transmitter system, Dopamine, Ligands, Limbic system, Motor end plate, Neuromuscular junction, Neurotransmitters, Nicotine, Noradrenergic neurotransmitter system, Parkinson’s disease, Peripheral nervous system (PNS), Synapse, Synaptic cleft, Vesicles