A toxin found in shellfish blocks voltage-gated Na+ channels from opening in somatic motor neurons. What...

A toxin found in shellfish blocks voltage-gated Na+ channels from opening in somatic motor neurons. What effect would this have on nerve and muscle function?

Neurons wouldn’t depolarize; muscle would contract continuously (spastic paralysis)

Neurons wouldn’t repolarize; muscle would be unable to contract (flaccid paralysis)

Neurons wouldn’t repolarize; muscle would contract continuously (spastic paralysis)

Neurons wouldn’t depolarize; muscle would be unable to contract (flaccid paralysis)

Neurons wouldn’t depolarize, but this would not affect muscle function

Expert Solution

Correct answer:

Neurons wouldn't depolarize; muscle would be unable to contract. (Flaccid paralysis)

Explanation:

When a nerve impulse reaches the motor neuron, it activates the voltage-gated Na+ channels
This causes an influx of Na+ into the nerve cell.
This causes depolarization of the neuron
When the nerve action potential reaches the motor endplate, it causes the release of neurotransmitter (Acetylcholine) is released in the synaptic cleft ( space between the nerve end and muscle)
The acetylcholine binds to the receptors in the muscle fiber and induces Na+ influx into the skeletal muscle.
This depolarizes the muscle. This leads to calcium release.
The release of calcium causes the skeletal muscle to contract.
This is called excitation-contraction coupling
As the toxin is going to block the voltage-gated Na+ channel, it will prevent the development of action potential in the motor neuron.
As there is no action potential development in the motor neuron, there will be no muscle contraction (Flaccid paralysis)

Incorrect answer:

First option: Incorrect - if depolarization doesn't occur, muscle contraction will also not occur

Second and third option: Incorrect - Inhibition of the voltage-gated Na+ channels on the nerve fibers will prevent depolarization but not induce repolarization.

Fifth option: Incorrect - if depolarization doesn't occur, muscle contraction will also not occur. So it does influence the muscle contraction.

Sydney Mullin answered 1 year ago

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