Eyes and hyperpolarization

[glam407]

Hi Guys so I was wondering if someone can answer my question.

A) How does closing the Na+ channel read to hyperpolarization? So in a cell there is the Na+/K+ pump, so if the channel is closed, the Na+ can't be pumped out, but the K+ is still pumped in-- so this would lead to a more positive charge? not hyperpolarization? I guess I'm really confused.

B) And for the eye, does the light hit the ganglia -> bipolar cells -> rods & cones?

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[Jas1360]

Hi Guys so I was wondering if someone can answer my question.

A) How does closing the Na+ channel read to hyperpolarization? So in a cell there is the Na+/K+ pump, so if the channel is closed, the Na+ can't be pumped out, but the K+ is still pumped in-- so this would lead to a more positive charge? not hyperpolarization? I guess I'm really confused.

B) And for the eye, does the light hit the ganglia -> bipolar cells -> rods & cones?

A) At the top of a normal action potential the Na+ channel closes but a K+ channel opens and allows K+ to leave the cell because there are more potassium ions on the inside of the cell than the outside of the cell. So as the K+ is rushing out, the cell can become hyperpolarized.

 

[Postictal Raiden]

Hi Guys so I was wondering if someone can answer my question.

A) How does closing the Na+ channel read to hyperpolarization? So in a cell there is the Na+/K+ pump, so if the channel is closed, the Na+ can't be pumped out, but the K+ is still pumped in-- so this would lead to a more positive charge? not hyperpolarization? I guess I'm really confused.

B) And for the eye, does the light hit the ganglia -> bipolar cells -> rods & cones?

I think you are confused between the Na/K pump and the ion channels. They are not the same thing. Pumps utilize active transport to "pump" ions against their gradients, while channels "passively" facilitate the transport of ions down their gradient. If the sodium channel is closed, no more sodium enters the cell. Meaning, less positive charge influx. Furthermore, potassium channels open and allow potassium to efflux out of the cell, leading to a net loss of positive charge. This causes the cell to become more negatively charged compared to the extracellular environment. This is known as hyperpolarization.

For my best knowledge, the sodium/potassium pump is not directly involved in generating action potential. Instead, it plays role in maintaining the electrochemical gradient across the cell membrane.

 

[Hemorrage]

Hi Guys so I was wondering if someone can answer my question.

A) How does closing the Na+ channel read to hyperpolarization? So in a cell there is the Na+/K+ pump, so if the channel is closed, the Na+ can't be pumped out, but the K+ is still pumped in-- so this would lead to a more positive charge? not hyperpolarization? I guess I'm really confused.

B) And for the eye, does the light hit the ganglia -> bipolar cells -> rods & cones?

You are getting this all mixed up.

1. Na+ concentration is always higher outside the cell and K+ is higher inside the cell under normal conditions.
2. So there are two elements to consider when understanding the membrane potentials. Ions can diffuse across the gradient via electrostatic attraction AND concentration gradient. What does this mean? Lets talk about K+. K+ is motivated to leave the cell due to the high concentration of K+ inside, however, the inside of the cell contains LOTs of organic phosphates and other negatively charged compounds that electrostatically attract the K+ and influence it to stay inside the cell. This is what the nerst equation predicts, the nerst equation predicts the membrane potential where electrostatic attraction for an ion to stay in its environment equals the motivation to leave an area of high concentration. You can apply the same principle to Na+.
3. The resting membrane potential of a cell is around -70mv relative to the environment
4. There are more K+ leak channels than there are Na+ leak channels. (Note these are not Na/K pumps)
5. When an action potential is triggered, Na+ rushes into the cell however the K+ channels stay shut for a short period of time and this is what "depolarizes" the cell. Now you have a ton of Na+ and K+ inside the cell, the K+ channels open and K+ rushes out of the cell to restore the resting membrane potential. Now we have a problem, we need a high concentration of K+ inside and Na+ outside, so this is where the Na/K pump comes in. It pumps 3 Na out of the cell and 2 K in which restores the concentration gradients of both ions.

What you should realize is that the resting membrane potential is -70mv because there are more K+ leak channels than there are Na+ leak channels. The equilibrium potential for K+ is -90 mv and therefore -70 mv is closer to -90.

 

[image187]

what the above poster said for the mos part. As for the eyes, the retina
is broken down into a bunch of layers (google) them, with the "photoreceptor cells", otherwise known as Rods and cones located closer to the back of the eye... the bipolar, ganglion, and other cells on top, and the layer of nerve fibers that eventually make up the optic nerve resting on top of this all. Light passes through the lens and vitreous fluid as well as all these layers, and gets absorbed by pigments in the rods and cones underneath all these layers. A change in conformation of the pigment
occurs as well as energy release and transfer, which leads to potentials being created
by these cells.

 

[image187]

on a side note, the brain is amazing. If you think about all the
crap in the eye that the obstructs the lights path as it reaches our photoceptor cells (nerve fibers, vitreous fluid, a bunch of cell bodies), it's amazing our vision is as clear as it is. The brain basically receives a crappy picture of the external world and just fills in all the holes for us

 

[Laureatebarrel]

Go to youtube and search for an example that will make it easy to understand.