MCAT Biology Question 57: Answer and Explanation

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Question: 57

12. An autoimmune disease attacks the voltage-gated calcium channels in the nerve terminal. What is a likely symptom of this condition?

  • A. Spastic paralysis (inability to relax the muscles)
  • B. Flaccid paralysis (inability to contract the muscles)
  • C. Inability to reuptake neurotransmitters once released
  • D. Retrograde flow of action potentials

Correct Answer: B

Explanation:

First, consider the function of voltage-gated calcium channels. When the nerve terminal depolarizes, voltage-gated calcium channels open, allowing for influx of calcium. This influx of calcium triggers fusion of the synaptic vesicles containing neurotransmitters with the membrane of the neuron at the nerve terminal. This allows for exocytosis of the neurotransmitters into the synapse. If a disease blocked the influx of calcium, there would be no release of neurotransmitters. A lack of neurotransmitters means that the neuron cannot send signals. Thus, any symptoms resulting from this disease would be due to an inability of neurons to communicate. If neurons cannot communicate, flaccid paralysis may be one of the results.

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