What happens when the membrane potential of a neuron reaches the threshold level?

A) Voltage-gated sodium channels open, and sodium diffuses out of the cell.
B) Voltage-gated potassium channels open for a very brief period.
C) Voltage-gated sodium channels close, so sodium cannot diffuse out of the cell.
D) The sodium channel protein changes its shape to open the gates of the channel.
E) The membrane potential is more negative than when at rest.