Question

Assertion : The resting membrane of the neuron exhibits polarity of charges
Reason : The outer surface of the axonal membrane possesses a negative charge while its inner surface becomes positively charged

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (C)

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 high concentration of $K^{+}$ and negatively charged proteins and low concentration of $Na^{+}$. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodiumpotassium pump which transports $3 \,Na^{+}$ outwards for $2$ $K^{+}$ into the cell. As a result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised