Etrodotoxin is a potent toxin found in a variety of organisms including the pufferfish. The toxin binds to the extracellular side of the Na + channel and prevents channel opening. This leads to paralysis of muscles, including the diaphragm. Death from respiratory failure can occur after ingestion of as little as 1 mg of the toxin. Why does this toxin cause paralysis?

Choose one:

A. The membrane depolarization is not amplified along the axon.

B. The Na + channel does not open wide enough to allow enough Na + through the channel.

C. The Na + channels remain in the inactive, refractory state.

D. The axon membranes become over-depolarized.

C

Explanation:

Tetrodotozin is a sodium channel blocker. that is; it prevents the opening of sodium channels in the neuron needed for depolarization and action potential production.

The voltage gated sodium channels in the nerves and skeletal muscles are blocked, action potential are not generated from these areas, Therefore potassium channels are permanently open leading to hyper polarization, and since sodium channels can not open, they remain in refractory state, this leads to muscular paralysis leading to impairments of respiratory and cardiac functions.

Specifically the paralysis of the diaphragm muscles, lead to collapse of the lungs, preventing breathing, leading to suffocation and death.

This is an example of competitive inhibition; The introduction of cholinergic acetycholine neurotransmitter reverses the blockage of sodium channels