At the threshold for an action potential in a neuron:
E. All of the above are true.
Here's an explanation of the choices:
A. The membrane voltage is less negative than the resting membrane potential.
- The threshold for an action potential is a specific membrane potential value, typically more positive (less negative) than the resting membrane potential. When the membrane potential reaches this threshold, it signals the start of an action potential.
B. Voltage-gated sodium channels open.
- When the threshold potential is reached, voltage-gated sodium channels open. This increases the permeability of the neuron membrane to sodium ions (Na+).
C. Na+ influx exceeds K+ efflux.
- At the threshold potential, the influx of sodium ions (Na+) through the voltage-gated sodium channels becomes greater than the efflux of potassium ions (K+) through their respective channels. This creates a net positive charge inside the neuron.
D. An action potential is triggered.
- The opening of the voltage-gated sodium channels and the significant influx of Na+ ions result in the rapid depolarization of the neuron, thus triggering an action potential.
Since all of these statements describe events that occur when a neuron reaches threshold potential, the correct answer is E. All of the above are true.
