Neuronal Membrane at Rest Flashcards by Simon Blum

What is the equilibrium potential for Na+?

62 mV

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Key channels in determining a neurons resting membrane potential (Vm)

K channels

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Conducts signal without loss of strength; required to send fast signals down long axons (charge replenished all the way down)

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What must the plasma membrane have to generate a rest pot?

High resistance when channels are closed, can act as a capacitor

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What controls the movement of ions in cells?

Diffusion and electrical forces

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Made up of 4 separate proteins that form the pore

K channels

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Secondary protein structure

Alpha helices and beta pleated sheets

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What must membrane proteins have to generate a rest pot?

Specific proteins localized to soma, dendrites, axon (specific proteins at specific locations)

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How much current flows depends on these two things

Electric potential (voltage V)

2. electrical conductance

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What is the equilibrium potential for Ca2+?

123 mV

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The potential difference that balances the ionic concentration gradient for any given ion (the voltage that balances diffusion)

Ionic equilibrium potential

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Changing the concentration of this outside can cause the cell to depolarize, application seen in lethal injections

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What do excitable cells have at rest?

A resting membrane potential which is negative (inside compared to out)

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What three things are involved in generating a resting potential?

Cytosol and extracellular fluid, plasma membrane, and membrane proteins

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How does a cell develop a rest pot?

Controlling what ions can move across the membrane

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Something that stores charge

Capacitor

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4 protein structures

primary, secondary, tertiary, and quaternary

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How does rest. pot. vary between neurons? What does -65 represent?

Different types have different rest pots and -65 is the average

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Forms barrier to water and ions and allows membrane potentials to form

Phospholipid bilayer

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What produces large changes in membrane potential?

Tiny changes in ionic concentrations ( ~.00001 M)

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Ions are surrounded by clouds of water called this in the cytosol and extracellular fluid

Spheres of hydration

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A measure of the difference in charge between anode and cathode (force on particle), more difference = more current

Voltage

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What do ions move across the membrane at a rate proportional to?

Ions move across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential for an ion (driving force)

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What is the protein structure of many channels?

Quaternary

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Uses ATP for energy to exchange internal Na+ for external K+

Na/K pump

Occurs when diffusional and electrical forces are equal and opposite (they are in balance) (voltage that balances diffusion)

Equilibrium state

Made up of 1 protein that folds up to look like 4 to form the pore

Na channels

Equation to calculate the exact equilibrium potential for an ion

Nernst equation

Mutations to these lead to severe neurological problems or death (channelopothies)

K channels

What must the cytosol and extracellular fluid have to generate a rest pot?

Each needs a specific ion concentration and composition

What are the properties of every cell determined by?

Types of proteins expressed in membranes and cytosol

These are produced by the movement of ions, which follow the basic electrical principles

APs

Transports Ca2+ out of the cell, other proteins and channels help as well

Ca2+ pump

The cells can generate APs like nerve impulses and spikes (neurons and cardiac cells)

Excitable cells

What is the equilibrium potential for Cl-?

-65 mV

Voltage across the membrane

Membrane potential (Vm)

Calculates membrane potential of a cell at any given time (Vm)

Goldman equation

Work against concentration gradient to maintain concentration difference

Ion pumps

The Goldman equation accounts for this whereas the Nernst equation doesnt

Relative permeability to multiple ions

Each ion has its own one of these

Ionic equilibrium potential

What is the equilibrium potential for an ion inversely related to ?

Charge

These are the major charge carrier in the cytosol/extracellular fluid

Ions

To conduct an AP, what must a cell have?

A resting potential

Tertiary protein structure

Folding into subunit (many stop here)

Is the relative ability for a charge to move from one place to another, depends on number of particles available to carry the charge and how easily these can travel (is the channel open/how open)

Conductance (g, Siemens)

How much more K+ is inside than outside?

20x more inside

This conduction of a signal only works for short distances; for the most part cant send signals quickly (current carried by short range diffusion)

Passive conduction

First cloned in fruit fly, but not the one that sets the resting potential

K channels

Concentrations of K+, Na+, and Cl- inside/outside

``` K = higher in Na = higher out Cl = higher out ```

Where do the net differences in charge occur?

At the inside and outside surfaces of the membrane (5nm thick)

What can changing K concentration outside the cell cause?

Change in membrane potential

I (electrical current) = g (conductance) * V (voltage)

Ohm's law

How is the equilibrium potential for K+ made?

Diffusion wants K+ to leave and electrical forces want it to stay in

What is the neuron resting potential

-65 mV

These two determine whether the inside of a cell is positive or negative at equilibrium for each ion

Charge and concentration difference

What is the equilibrium potential for K+?

-80 mV

What determines the properties of the 20 amino acids?

R groups

Ions important for neurophysiology

Ca2+, K+ (only one higher inside), Na+, and Cl-

This channel being cloned in fruit flies lead to isolation of many other of these channels and understanding of many channel structures

K channels

Each ion has a different one of these calculated from the concentration difference across the membrane

Equilibrium potential

How does K spatial buffering occur and what is it?

Astrocytes pick up K and distribute it around to not let one area get too high in concentration

What happens when V=0?

No current flows even if channels are open

What is the membrane potential close to and why?

Close to equilibrium potential for K (Ek) due to high permeability of cell to K

Involved in the blood brain barrier (muscle not protected)

External K concentration

Knowing 2 of these 3 can be used to determine the other

Charge, higher concentration inside or outside, and equilibrium potential of the ion

These are important for how ions move through channels

Spheres of hydration

How does myelination help create a net difference in charge and get rid of the membrane capacitor problem?

Myelination separates + and - charges from each other for faster signaling (faster APs)

Chains of amino acids are called this and held together buy these

Polypeptide, peptide bonds

What are proteins made of?

One or more polypeptides

Used manipulation of the external K concentration to show that resting potential is mostly set by K permeability of neuron

Hodgkin and Katz

The relative inability of an electric charge to migrate (inverse of conductance)

Resistance (R, ohms)

Have both hydrophobic and hydrophilic regions, are selective, and can be controlled

Ion channels

What happens when g=0?

No current flows even if a voltage difference

What is the equilibrium potential for K+?

-80 mV

What would happen without the negative potential inside a neuron?

No transmission

These modulate K levels

Astrocytes

What is an example of a K channel mutation

Losing selectivity to K and allowing Na in and the resting potential is raised

What do simple reflex actions require?

Rapid signaling and integration of info

The inside of the cell is more this than the outside

Negative

Vm (membrane potential) - Eion (equilibrium potential for an ion)

Driving force

Major component of cytosol and extracellular fluid

Water

What does the membrane act like in generating net differences in charge? Why is this a bad thing?

It acts as a capacitor (stores charge) and it is not a good thing because it inhibits fast electrical signaling

Movement of charge, positive in the direction of positive charge movement

Electrical current (I)

How does an AP occur?

A brief reversal of charge, not reversal of gradient

This forms a high resistance barrier to ion until ion channels are opened

Lipid bilayer

Quaternary protein structure

Joining of multiple subunits into 1

Positioning of phospholipids in bilayer

Hydrophilic heads toward water (outside) and hydrophobic tails towards inside of membrane

Primary protein structure

Chain of amino acids

What voltage does an AP peak at?

30 mV

How do ions move into a cell in terms of direction?

Move in direction that moves the cell towards the equilibrium potential for that ion

Uses 70% of brain ATP, active transport, and electrical trial signaling won't work without it

Na/K pump

Transport ions across membranes against concentration gradients using ATP as the energy source

Pumps

What generates the average resting potential of a neuron?

Constant leak of K+ from the cell through leak channels (K+ is constantly diffusing out causing a - charge inside)

What do ions need to be able to move by diffusion?

Channels

Random movement from region of high concentration to low concentration, temp dependent (faster when warmer), must have a path through the lipid bilayer (like a channel)

Diffusion