Illustration of the toxic alkaloid d-tubocurarine, or DTC, complexed with a nicotinic acetlycholine receptor. DTC is derived from the South American plant Chondrodendron tomentosum and is used by the indigenous peoples as an arrow poison. It has also been used in Western medicine as a muscle relaxant. The receptor for the neurotransmitter acetylcholine controls electrical signalling between nerve and muscle cells, resulting in muscle contraction. Binding of tubocurarine to the receptor prevents the binding of acetycholine and therefore inhibits muscle contraction.