Question

Which of the following option correctly defines the function of sodium $-$ potassium pump?

• A. $N{a}^{+}$ and $K^{+}$ out of the neuron
• B. $N{a}^{+}$ and $K^{+}$ into the neuron
• C. $N{a}^{+}$ into the neuron and $K^{+}$ out of the neuron
• D. $K^{+}$ into the neuron and $N{a}^{+}$ out of the neuron

Answer 1

Answer: (D)

Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions. When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions (K⁺) and nearly impermeable to sodium ions (Na⁺). Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains a high concentration of K⁺ and negatively charged proteins and low concentration of Na⁺. In contrast, the fluid outside the axon contains a low concentration of K⁺, a high concentration of Na⁺ and thus forms a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na⁺ outwards for 2 K⁺ into the cell.