The Effects of Curare on Nerve Impulse

Although curare is a potential nervous-system poison, medical texts, including "Goodman & Gilman's Pharmacological Basis of Therapeutics," agree on one thing: the discovery of its effects on nerve impulse was a milestone for anaesthesia practice, which opened the way for the discovery of better and safer muscle relaxants.

Curare is a generic term for South American arrow poisons, usually from the strychnos toxifera or chondrodendron tomentosum plants. Also known as tubocurarine, curare functions as a neuromuscular blocking agent, or muscle relaxant.

Curare acts at the junction between the nerve and muscle to block the transmission of nerve impulses. Nerve impulses are electrochemical messages that propagate along nerve fibres and muscle cells to produce an action.

Curare competes with acetylcholine--or Ach--for receptors on muscle cells. Acetylcholine is a chemical messenger that normally transmits nerve impulses and activates muscle receptors.

When curare binds instead of acetylcholine, the receptors do not become activated, and there is loss of muscle function, paralysis and possibly death. Dosage and dosing intervals all determine the severity of curare's effect.

Curare immobilises muscles minutes after injection. However, its effects on nerve impulses are reversible and do not damage the nerve fibres.

Anti-cholinesterase drugs, such as physostigmine or neostigmine, can reverse the effects of curare poisoning. These drugs block acetylcholine breakdown at the neuromuscular junction, so acetylcholine molecules can outnumber curare and activate unoccupied muscle receptors.