NCERT Class 11 Science — Chapter 8: Neural Control and Coordination

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Which combination correctly represents the action of the sodium-potassium pump in neurons?

Official previous-year question

Verified 1 Aug 2026.

Options

A3 Na+ in, 2 K+ out
B2 Na+ in, 3 K+ out
C2 Na+ out, 3 K+ in
D3 Na+ out, 2 K+ in

Did you get this right?

Solution

The correct option is 3 Na+ out, 2 K+ in.

Explanation

The sodium-potassium pump ($Na^+$-$K^+$ ATPase) is a vital transmembrane protein found in the plasma membrane of neurons. It functions as a primary active transport mechanism, utilizing energy from ATP hydrolysis to move ions against their concentration gradients.

Mechanism of Action:

Sodium Transport: The pump binds intracellular sodium ions. Upon the hydrolysis of one ATP molecule, the pump undergoes a conformational change and transports 3 Sodium ions ($Na^+$) out of the cell.
Potassium Transport: Subsequently, the pump binds extracellular potassium ions and transports 2 Potassium ions ($K^+$) into the cell as it returns to its original conformation.

This stoichiometry (3 positive charges exiting for every 2 positive charges entering) creates a net deficit of positive charge inside the neuron. This electrogenic nature is fundamental in establishing and maintaining the resting membrane potential (typically -70 mV) required for nerve impulse transmission.

Key Takeaway: The specific stoichiometry of the sodium-potassium pump is 3 $Na^+$ OUT and 2 $K^+$ IN per ATP molecule.

Your note

More from Chapter 8: Neural Control and Coordination

With reference to coordination in the human body, consider the following statements: 1. Neural pathways enable rapid point-to-point signalling. 2. Hormones provide electrical integration across organs. 3. Both systems jointly ensure synchronised organ function. Which of the statements given above are correct?

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Consider the following statements about synapses: 1. Electrical synapses transmit faster than chemical synapses. 2. Chemical synapses have closely apposed membranes with no cleft. 3. Electrical synapses are rare in humans. Which of the statements given above are correct?

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Assertion (A): Impulse transmission across an electrical synapse is very similar to impulse conduction along a single axon. Reason (R): At electrical synapses, the membranes of the pre- and post-synaptic neurons are in very close proximity, allowing current to flow directly.

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Consider the following statements: 1. The cerebral cortex contains only motor areas. 2. Association areas are responsible for intersensory associations, memory and communication. 3. Sensory areas are present in the cortex. Which of the statements given above are correct?

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Assertion (A): In a resting neuron, the axonal membrane is positively charged outside and negatively charged inside. Reason (R): The sodium-potassium pump transports 3 Na+ into the cell for every 2 K+ transported out.

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The correct option is 3 Na+ out, 2 K+ in.

Explanation

Mechanism of Action:

Sodium Transport: The pump binds intracellular sodium ions. Upon the hydrolysis of one ATP molecule, the pump undergoes a conformational change and transports 3 Sodium ions ($Na^+$) out of the cell.
Potassium Transport: Subsequently, the pump binds extracellular potassium ions and transports 2 Potassium ions ($K^+$) into the cell as it returns to its original conformation.

Key Takeaway: The specific stoichiometry of the sodium-potassium pump is 3 $Na^+$ OUT and 2 $K^+$ IN per ATP molecule.