free energy for this reaction is rather small (DG–3.5 kcal/mol).

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#Unit 7. System Physiology – Animal

The entry of Na+ causes the opening of more voltage- gated Na+ channels and further depolarization, setting up a positive feedback loop .

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#Unit 7. System Physiology – Animal

The membrane potential moves toward the equilibrium potential for Na+ (+60 - +65mV) but does not reach it during the action potential, because the increase in Na+ conductance is short-lived.

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#Unit 7. System Physiology – Animal

The Na+ channels rapidly enter a closed state called inactivated state and remain in this state for a few milliseconds

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#Unit 7. System Physiology – Animal

Voltage-gated sodium channel has two gates:

activation gate near the outside of the channel 

Inactivation gate near 

the inside of the channel 

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#Id: 5439

#Unit 7. System Physiology – Animal

During overshoot  

the direction of the electrical gradient for Na+ is reversed because the membrane potential is reversed & this limits Na + influx 

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#Id: 5440

#Unit 7. System Physiology – Animal

During overshoot 

the voltage-gated K+  channels open & contribute to repolarization