acetylcholine

Physiology

(noun)

An organic, polyatomic cation (often abbreviated ACh) that acts as a neurotransmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms, including humans.

Related Terms

  • Biogenic amines
  • glutamate
  • parasympathetic nervous system
  • lacrimation
  • neurotransmitter
  • dopamine
  • opioid

(noun)

This neurotransmitter acts on the neuromuscular juncture and is synthesized from acetic acid and choline.

Related Terms

  • Biogenic amines
  • glutamate
  • parasympathetic nervous system
  • lacrimation
  • neurotransmitter
  • dopamine
  • opioid
Biology

(noun)

a neurotransmitter in humans and other animals, which is an ester of acetic acid and choline

Related Terms

  • parasympathetic nervous system
  • tropomyosin
  • preganglionic
  • cranial nerve
  • sympathetic nervous system
  • sarcoplasmic reticulum
  • spinal nerve
Microbiology

(noun)

A neurotransmitter in humans and other animals. It is an ester of acetic acid and choline with chemical formula CH3COOCH2CH2N<sup>+</sup>(CH3)3.

Related Terms

  • neurotoxin
  • axon

Examples of acetylcholine in the following topics:

  • Cholinergic Neurons and Receptors

    • Acetylcholine is also the principal neurotransmitter in all autonomic ganglia.
    • Acetylcholine was first identified in 1914 by Henry Hallett Dale for its actions on heart tissue.
    • Acetylcholine was also the first neurotransmitter to be identified.
    • When acetylcholine binds to acetylcholine receptors on skeletal muscle fibers, it opens ligand-gated sodium channels in the cell membrane.
    • This human M2 muscarinic acetylcholine receptor is bound to an antagonist (ACh).
  • Agonists, Antagonists, and Drugs

    • Blocking, hindering, or mimicking the action of acetylcholine has many uses in medicine.
    • Atropine's pharmacological effects are due to its ability to bind to muscarinic acetylcholine receptors.
    • A nicotinic agonist is a drug that mimics, in one way or another, the action of acetylcholine (ACh) at nicotinic acetylcholine receptors (nAChRs).
    • They are ligand-gated ion channels with binding sites for acetylcholine as well as other agonists.
    • In 2009 there were at least five drugs on the market that affect the nicotinic acetylcholine receptors.
  • Peripheral Motor Endings

    • In vertebrates, the signal passes through the neuromuscular junction via the neurotransmitter acetylcholine.
    • Acetylcholine diffuses into the synaptic cleft and binds to the nicotinic acetylcholine receptors located on the motor end plate.
    • This blockage of acetylcholine receptors causes muscle weakness, often first exhibiting drooping eyelids and expanding to include overall muscle weakness and fatigue.
    • The binding of acetylcholine at the motor end plate leads to intracellular calcium release and interactions between myofibrils to elicit contraction.
    • Detailed view of a neuromuscular junction: 1) Presynaptic terminal; 2) Sarcolemma; 3) Synaptic vesicle; 4) Nicotinic acetylcholine receptor; 5) Mitochondrion.
  • Paralysis-Causing Bacterial Neurotoxins

    • Botulinum toxin is a protein and neurotoxin, which blocks neuromuscular transmission through decreased acetylcholine release.
    • In 1949, Arnold Burgen's group discovered, through an elegant experiment, that botulinum toxin blocks neuromuscular transmission through decreased acetylcholine release.
    • This light chain is an enzyme (a protease) that attacks one of the fusion proteins (SNAP-25, syntaxin or synaptobrevin) at a neuromuscular junction, preventing vesicles from anchoring to the membrane to release acetylcholine.
    • By inhibiting acetylcholine release, the toxin interferes with nerve impulses and causes flaccid (sagging) paralysis of muscles in botulism, as opposed to the spastic paralysis seen in tetanus.
    • The SNAP-25 protein is required for vesicle fusion that releases neurotransmitters from the axon endings (in particular acetylcholine).
  • Parasympathetic Responses

    • The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter, although peptides (such as cholecystokinin) may act on the PSNS as neurotransmitters.
    • Two different subtypes of nicotinic acetylcholine receptors with alpha and beta subunits are shown.
    • The acetylcholine binding sites are indicated by ACh.
  • Types of Neurotransmitters by Function

    • The major types of neurotransmitters include acetylcholine, biogenic amines, and amino acids.  
    • Acetylcholine, which acts on the neuromuscular junction, was the first neurotransmitter identified.
    • Once released, acetylcholine binds to post-synaptic receptors and is degraded by acetylcholinesterase.
    • Acetylcholine-releasing neurons are also found in the central nervous system (CNS).
  • Neurotransmitters

    • The cholinergic system is a neurotransmitter system of its own, and is based on the neurotransmitter acetylcholine (ACh).
    • Both of these receptors are named for chemicals that interact with the receptor in addition to the neurotransmitter acetylcholine.
    • Nicotine, the chemical in tobacco, binds to the nicotinic receptor and activates it similarly to acetylcholine.
    • When acetylcholine binds to the nicotinic receptor, the postsynaptic cell is depolarized.
    • However, when acetylcholine binds to the muscarinic receptor, it might cause depolarization or hyperpolarization of the target cell.
  • Function and Physiology of the Spinal Nerves

    • Nerves that release acetylcholine are said to be cholinergic.
    • In the parasympathetic system, ganglionic neurons use acetylcholine as a neurotransmitter to stimulate muscarinic receptors.
    • Instead the presynaptic neuron releases acetylcholine to act on nicotinic receptors.
    • Upper motor neurons release acetylcholine.
    • Acetylcholine is released from the axon terminal knobs of alpha motor neurons and received by postsynaptic receptors (nicotinic acetylcholine receptors) of muscles, thereby relaying the stimulus to contract muscle fibers.
  • Postganglionic Neurons

    • In the parasympathetic division, they are cholinergic and use acetylcholine as their neurotransmitter.
    • At the synapses within the ganglia, the preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons.
    • The postganglionic neurons of sweat glands release acetylcholine for the activation of muscarinic receptors.
    • The parasympathetic nervous system uses acetylcholine (ACh) as its chief neurotransmitter, although peptides (such as cholecystokinin) may act on the PSNS as a neurotransmitter.
  • Ionotropic and Metabotropic Receptors

    • The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor .
    • It consists of a pentamer of protein subunits with two binding sites for acetylcholine which, when bound, alter the receptor's configuration and cause an internal pore to open.
    • Examples of metabotropic receptors include glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, most serotonin receptors, and receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides, and endocannabinoids.
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