Nerve impulse generation and transmission — A/L Biology

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1. During the depolarization phase of an action potential in a human neuron, what molecular ion movement occurs across the axolemma?
   1. A) Rapid efflux of K⁺ ions through voltage-gated potassium channels
   2. B) Passive diffusion of Cl⁻ ions into the axon
   3. C) Rapid influx of Na⁺ ions through voltage-gated sodium channels
   4. D) Active pumping of 3 Na⁺ out and 2 K⁺ in via Na⁺/K⁺ ATPase
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   Correct answer: C) Rapid influx of Na⁺ ions through voltage-gated sodium channels

   Depolarization is caused by the rapid opening of voltage-gated sodium channels once threshold potential is reached, driving an overwhelming influx of Na⁺ down its electrochemical gradient into the intracellular fluid.

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   Step 1: Resting state: high Na⁺ outside, high K⁺ inside (-70 mV). Step 2: Threshold stimulated (-55 mV) → voltage-gated Na⁺ channels open. Step 3: Na⁺ rushes into axon down concentration and electrical gradients → membrane potential rises to +30 mV (depolarization). Step 4: Repolarization follows with K⁺ efflux. Answer: Rapid influx of Na⁺ ions through voltage-gated sodium channels.
   Modelled on: the A/L Biology examination pattern

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Where does Nerve impulse generation and transmission fit in the syllabus?

Year 2 · Term 1