Illustration of botulinum toxin molecules (green and purple) blocking neurotransmitter (yellow) release in a neurone (nerve cell). This neurotoxin, produced by the bacterium Clostridium botulinum, enters nerve cells and prevents release of neurotransmitters. This destroys communication pathways between nerve cells and leads to muscle paralysis, respiratory failure and death. Small amounts of botulinum toxin type A are used as a muscle relaxant.