Conotoxin is best described as a toxin that causes diaphragm paralysis by affecting neurotransmitter receptors and ion channels.

• A. Conotoxin
• B. Botulinum toxin
• C. Saxitoxin
• D. Tetrodotoxin

Answer: (A)

Think about how a toxin can stop the diaphragm from contracting by interrupting the signals nerves rely on at the neuromuscular junction. Conotoxins from cone snails are specialized to target neuronal receptors and ion channels. They can block nicotinic acetylcholine receptors at the neuromuscular junction and also interfere with voltage-gated ion channels, so nerve impulses fail to produce a muscle response. This combination of receptor and ion-channel disruption directly leads to diaphragm paralysis and potential respiratory failure.

Other toxins cause paralysis by different primary actions. Botulinum toxin prevents release of acetylcholine from nerve terminals, which is a disruption of neurotransmitter release rather than receptor or ion-channel blocking. Saxitoxin and tetrodotoxin mainly block voltage-gated sodium channels, stopping action potentials but not directly affecting receptors; their mechanism is narrower than the mixed receptor/ion-channel targeting seen with conotoxins.