Acetylcholine

Acetylcholine is a chemical messenger released by neurons to signal other neurons, muscle cells, and glands. Its effects depend on the receptors it activates.

Acetylcholine receptor: A membrane protein that binds acetylcholine and changes cell activity. These receptors determine which cells respond and whether their response is fast or gradual.
Neuromuscular junction: The synapse where a motor neuron communicates with a skeletal muscle fiber. Acetylcholine is the transmitter that normally initiates skeletal-muscle activation there.
Neurotransmitter: A chemical released by a neuron that transmits a signal across a synapse. Acetylcholine is one of the neurotransmitters used throughout the nervous system.
Norepinephrine: A neurotransmitter and hormone involved in alertness and sympathetic signaling. Many sympathetic target organs use norepinephrine rather than acetylcholine as their postganglionic transmitter.
Nicotinic acetylcholine receptor: A ligand-gated ion channel activated by acetylcholine and nicotine. At neuromuscular junctions, this receptor converts acetylcholine release into a muscle-cell electrical signal.
Autonomic nervous system: The nervous system that regulates involuntary functions through sympathetic and parasympathetic pathways. Acetylcholine signals at all autonomic ganglia and at most parasympathetic target organs.
Action potential: A rapid, propagating change in a cell's membrane voltage. An arriving action potential triggers calcium entry and acetylcholine release from nerve endings.
Glutamate: The principal excitatory neurotransmitter in the mammalian central nervous system. Glutamate dominates fast excitation in the brain, while acetylcholine often modulates circuit activity.
Muscarinic acetylcholine receptor: A G-protein-coupled receptor activated by acetylcholine and muscarine. These receptors mediate many slower acetylcholine effects in the brain, heart, and glands.
Botulinum toxin: A bacterial neurotoxin that blocks acetylcholine release at peripheral nerve endings. Its blockade of transmission at neuromuscular junctions causes flaccid paralysis.

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