Dear Prof,
I would appreciate it if you could look over my understanding about neurones and membrane resting potential.
Resting potential:
At resting, the membrane potential is at -71mV, which is near E(K) which is -75mV. This anomaly is caused by two reasons:
1. all background (leak) K+ channels open, allowing an efflux of K+ down its concentration gradient. By itself, this causes the membrane potential to be at -75mV. However,
2. some Na+ background channels are open, allowing Na+ to move down it's concentration gradient. This cancels some of the potential generated by the movement of K+ out of the cell.
At the same time, the membrane is not permeable to anions such as proteins and this causes a separation of charge across the membrane. Their interaction causes the generation of an electrical voltage.
Also, the Na+/K+ pump actively pumps K+ into the cell and Na+ out to mantain the resting membrane potential.
So, this takes place in all animal cells? And the voltage-gated Na+ channels are not involve in the maintenance of resting potential?
Generation of an action potential:
When a stimulus reaches a neuron, the Na+ channels open proportionately to the intensity of the stimulus which makes it graded. It is then transmitted electrotonically to the spike-generating zone of the neuron.
At the spike-generating zone, when the volatge reaches the threshold level, the voltage-gated Na+ channels undergo a comformational change, causing the gate to be open. This causes an influx of Na+ down its concentration gradient. The increase in permeability to Na+ causes more Na+ channels to open by positive feedback mechanism. As a result, the membrane potential is depolarised and reaches +55mV.
However, the inactivation gates of Na+ channels responds to the positive membrane potential and starts to close. Repolarisation then begins as the membrane becomes less impermeable to Na+.
Voltage-gated K+ channels starts to open, causing K+ to leave the cell and restore the resting potential.
At this stage, wouldn't there be an upset over the concentration of of both Na+ and K+? My answer would be that the Na+/K+ pump has to do it's part in restoring the resting potential.
I would appreciate it if you could look over my understanding about neurones and membrane resting potential.
Resting potential:
At resting, the membrane potential is at -71mV, which is near E(K) which is -75mV. This anomaly is caused by two reasons:
1. all background (leak) K+ channels open, allowing an efflux of K+ down its concentration gradient. By itself, this causes the membrane potential to be at -75mV. However,
2. some Na+ background channels are open, allowing Na+ to move down it's concentration gradient. This cancels some of the potential generated by the movement of K+ out of the cell.
At the same time, the membrane is not permeable to anions such as proteins and this causes a separation of charge across the membrane. Their interaction causes the generation of an electrical voltage.
Also, the Na+/K+ pump actively pumps K+ into the cell and Na+ out to mantain the resting membrane potential.
So, this takes place in all animal cells? And the voltage-gated Na+ channels are not involve in the maintenance of resting potential?
Generation of an action potential:
When a stimulus reaches a neuron, the Na+ channels open proportionately to the intensity of the stimulus which makes it graded. It is then transmitted electrotonically to the spike-generating zone of the neuron.
At the spike-generating zone, when the volatge reaches the threshold level, the voltage-gated Na+ channels undergo a comformational change, causing the gate to be open. This causes an influx of Na+ down its concentration gradient. The increase in permeability to Na+ causes more Na+ channels to open by positive feedback mechanism. As a result, the membrane potential is depolarised and reaches +55mV.
However, the inactivation gates of Na+ channels responds to the positive membrane potential and starts to close. Repolarisation then begins as the membrane becomes less impermeable to Na+.
Voltage-gated K+ channels starts to open, causing K+ to leave the cell and restore the resting potential.
At this stage, wouldn't there be an upset over the concentration of of both Na+ and K+? My answer would be that the Na+/K+ pump has to do it's part in restoring the resting potential.
Thanks,
Fairoz
0 Comments:
Post a Comment
Subscribe to Post Comments [Atom]
<< Home