Graded potentials

What are graded potentials

Localized ; occur in small area

Temporary

Changes in voltage across the membrane that dies off as they move along.

Graded potentials vary in amplitude , how come ?

the size of this change in membrane potential will be different at different places, and different places will have their potential.

Permeability also changes which allows channels to open or close

How does depolarization and hyper polarization occur

That is, that has to do with the channels that open for which specific ion.

If we open a sodium gated channel at the post synaptic membrane what will happen

Have a huge rush of sodium into the cell thanks to stimulus that set everything off

When sodium goes into the cell does it

It diffuses and goes away and others are being pumped out

As it travels across the membrane or cell it makes it most postive with wtv sodium hasn’t been diffused

At the end wtv sodium has been able to make it to axon hillock

Can set a trigger off to cause depolarization depends on if enough sodium had made it to set off an action potential

Depends on if it passed the threshold or not

What could cause the membrane to become more postive at the axon hillock

A graded potential

What happens if graded potential is able to reach threshold

both sodium and potassium voltage gated channels get the signal to open.

Na opens immediately

K+ opens at slower rate so takes longer to flood in

What happens when you reach peak of depolarization

voltage gated potassium channels open and voltage gated sodium channels are inactivated.

As a result potassium will leave the cell and cause repolarization

Now, when we get back to threshold, that's, again, a signal for both sodium and potassium voltage period channels to close their activation.

Sodium closed and becomes deactivated immediately

Potassium gets the same signal but takes longer to close which leads to hyper polarization

What happens when the sodium voltage gated channels finally close

You know, we have only leak channels so we’re going back to the resting membrane potential

Why is resting rate @-70

BC potassium leak channels

What is the threshold potential

-55 and whenever a stimulus reach this membrane potential it , causes depolarization

Action potential phase 1

Resting phase - V-G channels are closed but capable of being open

Phase 2

Depolarization

threshold is achieved VG channels for Na n K open

NA faster so enters cell fast

Repolarization

K VG channel open

NA becoming inactive

k leave cells

Hyper polarization

K VG closer as slower rate so caused this continues until it close

Back to normal

All.VG CHANNELS r closed , leak channels being back to resting -79

refractory periods are time periods

where new action potential can either not occur at all or be less likely.

ABSOLUTE refractory period

VG channels r open or inactivated

No new ACtion potential can be initiated

In absolute what can’t an action potential occur

Bc VG channels are already open so it can’t be fired if it’s already open

Or it’s closed with inactivation gate and can’t be opened

When threshold is reached again an action potential can occur again but it’s unlikely why ?

Bc the permeability of K is greater but it can reach action potential IF the stimulus to fire in sodium is much greater than K

Relative refractory period

So, it is harder to fire another action potential, because we have greater permeability for potassium.

It makes it harder for axon hillock reach threshold bc there is a bunch of forces that are pushing potassium out of the cell and trying to make the membrane potential more negative.

Propagation ; continuous conduction

In 3 sequences sodium will travel to the next area and next and next till it goes from depolarization to threshold to fire an action potential

One direction, same magnitude

In propagation as sodium travels to the next

So each area of the membrane as we move forward is activated, but as it is activated, the previous area is going to be in the absolute refractory period. Allows us to make sure signal only goes forward

What if we want something that’s faster than continuous conduction

We have saltatory conduction

Why is saltatory conduction faster

Regions of axon r covered by myelin sheats which are insulators. They're preventing. They're preventing the interaction between positive and negative ions. They completely insulate an area

What else does saltatory conduction contain

nodes of Ranvier, and nodes around here are just kind of all between these sheets. And these nodes around here has tons of sodium and potassium. So we can do it. We can jump from here to here and see what happens.

In saltatory when an action potential fires its cause’s depolarization which

Opens VG. Channels of sodium that travel at faster speeds thru the myelin sheaths bc it protects it and it continues to do so to achieve depolarization

So considering neurons and salvatory conduction, which we just talked about, what will be the result of this part of Ms considered its loosing its myelination

Negative charges will start to hold sodium which reduces the amount of sodium to make it to the next node of ranvier and reduce chances of depolarization