What happens during the depolarization phase of action potential?

• A. The neuron's internal charge becomes more negative.
• B. The neuron's membrane becomes more permeable.
• C. The neuron's internal charge becomes less negative, leading to a positive shift.
• D. The neuron is at resting potential.

Answer: (C)

During the depolarization phase of an action potential, the neuron's internal charge becomes less negative, which ultimately leads to a positive shift in the membrane potential. This process begins when a stimulus causes sodium channels in the neuron's membrane to open, allowing sodium ions (Na+) to flow into the cell. Since the concentration of sodium ions is much higher outside the cell compared to the inside, this influx of sodium causes the internal charge of the neuron to rise toward zero and then to become positive relative to the outside environment.

At this stage, the membrane potential transitions from the resting potential, which is typically around -70 mV, towards a more positive value. This eventual positive shift is crucial for the generation and propagation of action potentials along the neuron, enabling nerve impulses to travel efficiently. The ability of the neuron's membrane to undergo this change in charge is essential for effective communication between neurons.