29. A scientist is studying the effects of a new drug on the action potential of neurons. She observes that the drug binds to sodium channels and prevents them from opening. How would this drug most likely affect the action potential?
Answer: C
The drug would prevent the action potential from occurring.
By binding to sodium channels and preventing them from opening, the drug inhibits the influx of sodium ions, which is essential for the depolarization phase of the action potential. Consequently, this blockage would prevent the generation of action potentials in neurons.
A) The drug would increase the speed of the action potential.
This option is incorrect because the drug does not facilitate sodium channel opening; rather, it prevents it. Increased speed of action potential conduction is associated with enhanced sodium influx, which this drug actively inhibits.
B) The drug would cause the action potential to skip the depolarization phase.
This option is also incorrect because the depolarization phase is crucial for the action potential to occur. If sodium channels are blocked, depolarization cannot happen, meaning that the action potential cannot skip any phase but will fail entirely.
C) The drug would prevent the action potential from occurring.
This is the correct answer, as the drug's action of blocking sodium channels directly inhibits the necessary influx of sodium ions. Without this critical step, the action potential cannot be generated, and neural signaling is disrupted.
D) The drug would make the action potential threshold easier to reach.
This option is incorrect because the drug inhibits the opening of sodium channels, which are vital for reaching the action potential threshold. Instead of making it easier, the drug would make it more difficult, if not impossible, to reach that threshold.
Conclusion
The drug's mechanism of action—blocking sodium channels—directly prevents the occurrence of action potentials by obstructing the essential depolarization phase. All other options fail to address the fundamental role of sodium channels in action potential generation, demonstrating that only option C accurately reflects the drug's impact on neuronal activity.