Identify the key feature of the action potential that ensures it will travel only one direction.
1) the activation state of the voltage-gated K⁺ channel
2) the temporary cessation in activity of the Na⁺/K⁺ pump
3) the inactivation state of the voltage-gated Na⁺ channel
4) the inactivation state of the voltage-gated K⁺ channel
5) the activation state of the voltage-gated Na⁺ channel