A quaternary ammonium compound that cannot penetrate membranes.

The neurotransmitter of parasympathetic and somatic nerves as well as autonomic ganglia,

Acetylcholine is normally released by the parasympathetic nervous system (PSNS) at rest, and causes dilation of the coronary arteries.

It is therapeutically of no value because of its multiple actions and its rapid inactivation by the cholinesterases.

Acetylcholine has both muscarinic and nicotinic activity.

Acetylcholine decreases heart rate and cardiac output:.

Actions on the heart mimic the effects of vagal stimulation.

Acetylcholine binds to a post-synaptic nicotinic acetylcholine receptor.

A change in the receptor conformation allows an influx of sodium ions and initiation of a post-synaptic action potential. 

The action potential then travels along T-tubules until it reaches the sarcoplasmic reticulum. The depolarized membrane activates voltage-gated L-type calcium channels, present in the plasma membrane.

The L-type calcium channels are in close association with ryanodine receptors present on the sarcoplasmic reticulum.

Acetylcholine causes calcium ions to be released from the sarcoplasmic reticulum. 

The inward flow of calcium from the L-type calcium channels activates ryanodine receptors to release calcium ions from the sarcoplasmic reticulum. 

If injected intravenously, produces a brief decrease in cardiac rate and stroke volume as a result of a reduction in the rate of firing at the sinoatrial (SA) node.

Intravenous injection of acetylcholine causes vasodilation and lowering of blood pressure by activating M3 receptors found on endothelial cells lining the smooth muscles of blood vessels.

Activation of M3 receptors on endothelial cells by acetylcholine results in the production of nitric oxide from arginine.

Nitric oxide then diffuses to vascular smooth muscle cells to stimulate protein kinase G production, leading to smooth muscle relaxation.

Atropine blocks muscarinic receptors and prevents acetylcholine from producing vasodilation.

Increases salivary secretion and stimulates intestinal secretions and motility, increases bronchiolar secretions.

Increases the tone of the detrusor bladder muscle.

Stimulates ciliary muscle contraction for near vision and in the constriction of the pupillae sphincter muscle, causing miosis.

Acetylcholine 1% solution is instilled into the anterior chamber of the eye to produce miosis during ophthalmic surgery.

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