L3 Membrane Potentials​ Action Potentials

What affects the potassium concentration of the cell and how does this affect the resting potential?

Neurons have constant permeability K+ channels that formulate a charge difference across the cell​. If the constant permeabilty of the K+ channels changes, it will cause a charge difference to occur across the cell ​ Intracellular concentration of K+ is greater than the extracellular concentration​. Some K+ ions flow down a concentration gradient via K+ Leaky channels​ from inside the cell to the outside; causing resting potential to be more negative.

What causes the driving force for particle movement across a membrane?

Particles want to move from areas of high concentration to low concentration to reach equilibrium across the membrane. the larger the difference between the membrane potential and the equilibrium potential for a given ion, the larger the imbalance between electrical and concentration gradients and the larger the net movement of the ion​

What is the Goldman Equation and what is it used for?

Predicts the membrane potential based upon the concentration of several types of ions and the membranes permeability too each of those ions​ Most of the time, things are not at equilibrium; this is when we use the Goldman Equation​ Notes: -The membrane potential for Na+,K+ and Cl+ can all be calculated -Describes the membrane potential as a function of relative permeability of the cell membrane to more than a single species of ions​

action potential definition

-a rapid, all-or-none change in the membrane potential followed by a return to the resting membrane potential. -The basis of the signal-carrying ability of nerve cells. ​ -The patterns of conducted action potentials encode the information conveyed by nerve cells. ​ Notes: -All or none; it fires or it doesn't -it fires, the change in potential is different, then it returns to resting membrane potential​

What is the Nernst equation and what is is used for?

-predicting the electrical potential for various ions across the membrane at equilibrium Notes: -at equilibrium means at a standstill; no net flux of ions ​ ***WILL NOT BE ASKED TO CALCULATE WITH THIS EQUATION***​ Just be familiar w it and what its used for

Action Potential Propagation Requires Both Active and Passive Current Flow​. Explain the process.

General process in picture. *be able to talk through this diagram step by step; it is the basis for how an action potential works​ In depth explanations below: 1. When the stimulus hits the membrane, it causes the Na channels to open, and the Na+ goes in​ 2. Some of the current just becomes depolarized on its own and flows down w/out the need for Na+ channels to be opened and Na+ to flow thru​ 3. Not only is one Na+ channel open, but several neighboring Na+ channels become open (seen in red); and each action potential takes place at each Na+ channel​ 4. Bc the upstream Na+ channels are inactivated, Na+ no longer flows thru; but the K+ channels open, and K+ starts coming out; when that K+ starts flowing out, it causes the repolarization (cell membrane becomes more and more negatively charged bc you have the positive charge (K+) leaving the cell)​ 5. So, this process goes all the way down the membrane​

How does the size and shape of an action potential change along the length of an axon?

It doesn't; An action potential is propagated with the same shape and size along the entire length of an axon. ​

Resting potential

The voltage difference between the cytoplasmic and extracellular side of the plasmalemma.​ The cytoplasmic part will be negative​

What happens if the membrane is initially permeable to K+ and then temporarily switches to becoming most permeable to Na+?​ Why?

This would cause a depolarization (indicated by the rising of the line in the diagram). Resting membrane is more permeable to K+ than Na+ due to K+ leaky channels​. K+ naturally wants to leave the cell and Na+ naturally wants to enter the cell due to the the concentration gradient produced by the Na+ pump. If the membrane becomes more permeable to Na+ than K+, there will be more positive charges entering the cell than exiting; causing a depolarization of that membrane​ Side note: -The membrane is impermeable to negatively charged proteins (A-)​

What is the basis for action potentials?

Voltage-dependent ion channels in the plasma membrane

Where on the neuron are action potentials usually initiated?

at the initial segment of the axon, which is the part of the axon that is connected to the axon hillock of the cell body​

Thicker diameter of myelin =

faster velocity travelling down the axon​ Notes: myelinated at all will be faster than unmyelinated​

The Propagation of the Action Potential=

the advancement of an action potential in a single direction along the length of the membrane​

With unmyelinated axons, propagation of the action potential is dependent on..

the sequential activation of successive Na+ ion channels​ Notes for picture: -(Top figure, unmyelinated​) Think of the +s as Na+ ion channels​ -In order for an action potential to be conducted, each Na+ ion channel has to work​ -This takes some time​ -When they work and open, you have the sodium going into the cell, and the inside of the cell becomes more and more positive (depolarizing) all the way down; and it becomes more and more negative on the outside (which is secondary to the K+ channels that are opening and causing K+ to go out of the cell... this part confuses me... probably too much detail)​

Describe action potential conduction in a myelinated axon

voltage gated Na+ ion channels are farther apart and mainly clustered near the Nodes of Ranvier​. Current jumps from node to node making the process become much faster​ Notes for Bottom part of figure: Myelinated axon​ -The reason why the action potential is able to move so rapidly, compared to unmyelinated, is because there are clusters of voltage gated sodium ion channels in the Nodes of Ranvier. -Within those areas, rather than an action potential having to be created along the entire axon, the action potentials are simply clustering w/in these areas w/in the nodes of Ranvier; so we have action potentials jumping from node to node​ -This speeds up the time and is very efficient in comparison to the unmyelinated axon

At what action potential is the membrane said to be depolarized?

~40mV