Defining polarizations for Rod cells.

[pinkipod]

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Sorry if this was covered in another thread. I searched but couldn't find anything.

My understanding of definitions (for membrane potential)
Depolarization:
Potential moving away from resting membrane potential in the positive direction. (becoming more positive)
Repolarization:
Potential returning to resting membrane potential (becoming more negative but towards r.m.p.)
Hyperpolarization:
Potential moving away from resting membrane potential in the more negative direction (away from r.m.p)

I thought I got these concepts down until I encountered the membrane potential of rod cells.
1) Rod cells have a negative resting membrane potential like muscle & neurons due to Na leak channels.

2) Upon stimultation, V gated Na channels open, and they become hyperpolarized.
(In this sense, the definition for hyperpolarization is the same as that of muscle cells & neurons😉

3) Then, the potential returns to its resting membrane potential.
What kind of polarization would thie be? (Repolarization? Depolarization? Something else?)

thanks guys.

 

[Jorje286]

Technically, it's depolarization because the potential goes up after hyperpolarization. But I don't think this phase is called anything. Usually text books mention that the membrane potential is adjusted again back to its resting state after hyperpolarization.

 

[tncekm]

Jorje286 has got it 'fo 'sho. 🙂

Just to clarify, if it helps anyway, here are some more details (half of it was thinking myself through the process, so I just left it in the message 🙂)

I just went over this, so hopefully I've got it right.

Na+ flows relatively freely across the cell membrane at its resting potential. When they are stimulated the Na+ leak channels close and the cell becomes "hyper polarized" meaning that it is more polarized (a greater difference in electric potential on both sides). When the cell is hyper polarized, THEN it sends a signal. When the cell membrane returns to its normal potential it become "unhyperpolarized" meaning that the difference in electric potential is less, so it is less polarized, or depolarized.