Tetrodotoxin (TTX) is a chemical found in pufferfish which binds to voltage-gated sodium channels causing inactivation via a conformational change. Poisoning can result in paralysis leading to death. How might this occur? (4 marks)

This question asks about nerve action potential generation. There are a couple of clues - these include 'voltage-gated sodium channels' and 'paralysis' which suggests the idea of failure of impulse transmission along a neurone. Answering this question requires a good understanding of the different processes which occur during an action potential.A model answer would be: TTX blocks voltage-gated Na+ channels preventing an influx of sodium when the membrane is depolarised (by a generator potential) [1]. This prevents the rapid rising limb of the action potential from occurring [1] so that an impulse can no longer be transmitted along the neurone [1]. As a result, no neurotransmitter is released at the terminal/neuromuscular junction [1] and muscles cannot be stimulated to contract.There may be other structured parts to this question. For example: death is usually caused by respiratory failure resulting from the paralysis of the diaphragm - why does this result in death?