action potential 同 depolarization

So sorry to say that, I think you note (the first sentence) is wrong.因為Depolarization的定義是 the sudden reversal of the membrane potential
depolarization is the electrical change which occurs during the passage of the action potential這句是對的,因為它表示了nerve impulse怎樣去propagate.

我唔係好明..depolarization..我覺得佢講到好似同action potential差唔多.. 其實並非一樣,是有小小分別的.首先,在resting potential時,axon 外面的charge是正[因為這時Na+在axon 外面的濃度高過在axon入面的濃度, 而axon 裏面的charge是負,因為這時K+在axon入面的濃度高過出面axon的濃度
當depolarization(去極化)時,即是這個做成去極化的刺激(stimulus)的值(即其大小[magnitude])一定要大過能夠產生depolarization的臨界值(threshold value) 在下圖是 -55mV,而根據 all or nothing rule, it says.(甲) An action potential will not be produced if the magnitude of a stimulus is not greater than the threshold value required to generate the depolarization.即是說如果stimulus的臨界值是細過-55mV的話,無任何action potential產生.(乙)如果stimulus的magnitude是大過-55mV好多的話,例如 +300mV,產生出來的action potential會不會大過下圖的+40mV呢,答案是不會的.即使stimulus的magnitude是 +300mV,由它所產生出來的action potential都是+40 mV,而唯一不同的是會有更多action potential在這段時間產生.(Higher magnitude of stimulus will only cause more action potentials to be generated within this period. But for the magnitude of action potential, it won't be changed.)
請參考下圖,所謂去極化是指當stimulus的臨界值大過-55mV時,在membrane的電壓由-55mV升到+40mV(即圖中的rising phase),這是因為當stimulus的臨界值大過-55mV時, the Na+ voltage gated channels all open so that the permeability of the axon to Na+ ions increase abruptly and sharply.
當這個phase過去後,所有的Na+ voltage gated channels 會關起,而這時去極化已全部完,在這時,repolarization(復極化 ; 再極化)出現,即是K+ voltage gated channels 會打開,但所有的Na+ voltage gated channels 在這時候仍然關起來,這就出現了下圖由+40mV降到-70mV的情況(the K+ voltage gated channels will open and increase the permeability of K+ ions to flow into the axon .But for Na+ voltage gated channels, they remain close. )
When this phase passes, the K+ voltage gated channel still open letting more K+ ions go inside the axon. The membrane voltage is more negative下圖由-70mV降到更加負的數值.這個階段叫hyperpolarization.
當hyperpolarization完成時,the K+ voltage gated channel close again. 由在axon 中的Na+離子會由 K/Na ATP 泵走,Na+離子會由axon裏面泵出去axon外面(removed by K/Na-ATP pumps). The membrane potential returns to resting potential again.
這圖出於http://en.wikipedia.org/wiki/Depolarization

圖片參考：http://upload.wikimedia.org/wikipedia/en/7/78/Apshoot.jpg


總結




descriptions
outside an axon
inside an axon
stimulus

resting potential along the axon
+ve
-ve
細過threshold value required to cause depolarization 或無stimulus出現


action potential propagates along the axon 或有depolarization出現.
-ve
+ve
大過threshold value required to cause depolarization

Depolarization : is the sudden reversal of the membrane potential
如果你的NOTE無錯,而是我錯的話,可否電郵給我,(按ln3053ah再選寄信給他或她)告知在下呢?
I hope you will find my writing helpful

First ,when the stimulus occur Na channel opened ,the polarity is reversed because of

the Na ion diffuse into cell.It begin the depolarization of the membrane,


When a sufficient number of Na channels is opened = reach the threshold

It cause positive feedback to ensure action potential produced.

so depolarization will produce action potential is due to the strength of stimulus