The transfer of electrical signals by nerve cells in human body is enabled by
- A.sodium
- B.potassium
- C.iron
- D.sodium and potassium
Correct answer
Explanation
The correct answer is D, sodium and potassium. A nerve impulse is carried by the movement of sodium ions into the nerve cell and potassium ions out of it.
At rest, a neuron keeps more sodium outside and more potassium inside, using the sodium-potassium pump, which gives a resting potential of about −70 mV. When the cell is stimulated, sodium channels open and Na⁺ rushes in, making the inside positive (depolarisation). Potassium channels then open and K⁺ flows out, restoring the negative charge (repolarisation). This wave of change travels along the axon as the action potential.
A is wrong because sodium alone can start the impulse but cannot restore the resting state.
B is wrong because potassium alone only resets the membrane; it does not create the impulse.
C is wrong because iron's main role is in haemoglobin, carrying oxygen in the blood.
Exam tip: nerve impulse = Na⁺ in (depolarisation), K⁺ out (repolarisation); the Na⁺/K⁺ pump moves 3 Na⁺ out and 2 K⁺ in.
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