Which ion channels are primarily responsible for the depolarization phase of the action potential?

Which ion channels are primarily responsible for the depolarization phase of the action potential?

• A. Voltage-gated potassium (K+) channels
• B. Voltage-gated sodium (Na+) channels
• C. Ligand-gated Na+ channels
• D. Leak channels

Answer: (B)

Depolarization during an action potential is driven by the rapid opening of voltage-gated sodium channels in the axonal membrane. When the membrane reaches threshold, their activation gates swing open, allowing a large influx of Na+ that makes the inside of the cell much more positive and creates the rising phase of the spike. These channels then quickly inactivate, which ends the depolarizing current and leads into the repolarization phase driven by voltage-gated potassium channels. Potassium channels primarily handle repolarization, ligand-gated Na+ channels respond to neurotransmitters and mediate synaptic inputs rather than the spike itself, and leak channels contribute to the resting membrane potential.

Depolarization during an action potential is driven by the rapid opening of voltage-gated sodium channels in the axonal membrane. When the membrane reaches threshold, their activation gates swing open, allowing a large influx of Na+ that makes the inside of the cell much more positive and creates the rising phase of the spike. These channels then quickly inactivate, which ends the depolarizing current and leads into the repolarization phase driven by voltage-gated potassium channels. Potassium channels primarily handle repolarization, ligand-gated Na+ channels respond to neurotransmitters and mediate synaptic inputs rather than the spike itself, and leak channels contribute to the resting membrane potential.