The GAP for RAS (called a RAS-GAP) works by inserting one of its arginine side chains into the Ras active site, thus stabilizing an intermediate in the

hydrolysis reaction.

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#Unit 7. System Physiology – Animal

In response to a depolarizing stimulus, some of the voltage-gated Na+ channels open and Na+ enters the cell and the membrane is brought to its threshold potential (approximately −55 mV)

TLS Online TPP Program

#Id: 5435

#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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#Id: 5436

#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.

TLS Online TPP Program

#Id: 5437

#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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#Id: 5438

#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 

TLS Online TPP Program

#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