Which part of the neuromuscular junction is affected by botulinum toxin poisoning?

The neuromuscular junction is the site where nerve cells communicate with muscles. It consists of the motor neuron, the synaptic cleft, and the muscle fiber. Botulinum toxin poisoning affects the presynaptic membrane of the motor neuron, which is responsible for releasing acetylcholine, a neurotransmitter that triggers muscle contraction. Botulinum toxin blocks the release of acetylcholine, causing muscle weakness and paralysis.