Question

A nerve fibre is depolarized when it acquires

• A. A negative charge in the intracellular fluid and positive charge outside
• B. A positive charge in the intracellular fluid and negative charge outside
• C. A positive charge on both sides
• D. A negative charge on both sides

Answer 1

Answer: (B)

A positive charge in the intracellular fluid and negative charge outside

The polarised neuron is less permeable to the Na++ ions as compared to the K++ when at rest due to the activity of the Na++-K++ pumps. This makes the nerve fibre to acquire the negative charge as compared to the charge outside. The arrival of the threshold stimulus activates the voltage-gated Na++ channels due to which the Na++ ions move from the extracellular fluid to the intracellular fluid of the axon. This causes depolarization of the membrane and the nerve fibre acquires the positive charge as compared to the charge outside.

Hence, the correct answer is 'A positive charge in the intracellular fluid and negative charge outside'