What happens when the neuron reaches threshold (-55 mV)?

• A. Voltage-gated potassium channels open and potassium rushes into cell.
• B. Voltage-gated sodium channels open and sodium rushes into the cell.
• C. Voltage-gated potassium channels open and sodium channels close.
• D. The sodium potassium pump immediately establishes resting potential.

Answer: (B)

Verified step by step guidance

1. Understand the concept of action potential: Neurons communicate through electrical signals called action potentials. An action potential is initiated when the neuron reaches a specific membrane potential known as the threshold, typically around -55 mV.
2. Identify the role of voltage-gated sodium channels: At the threshold potential, voltage-gated sodium channels open. This allows sodium ions (Na+) to rush into the neuron due to the concentration gradient and electrical gradient.
3. Recognize the effect of sodium influx: The influx of sodium ions causes the membrane potential to become more positive, leading to the depolarization phase of the action potential.
4. Differentiate between sodium and potassium channels: While sodium channels open at the threshold, voltage-gated potassium channels open later, during the repolarization phase, allowing potassium ions (K+) to exit the cell.
5. Clarify the role of the sodium-potassium pump: After the action potential, the sodium-potassium pump helps restore the resting potential by moving sodium ions out of the cell and potassium ions back into the cell, but it does not act immediately at the threshold.