Neuronal Membrane at Rest Flashcards
What is the equilibrium potential for Na+?
62 mV
Key channels in determining a neurons resting membrane potential (Vm)
K channels
Conducts signal without loss of strength; required to send fast signals down long axons (charge replenished all the way down)
AP
What must the plasma membrane have to generate a rest pot?
High resistance when channels are closed, can act as a capacitor
What controls the movement of ions in cells?
Diffusion and electrical forces
Made up of 4 separate proteins that form the pore
K channels
Secondary protein structure
Alpha helices and beta pleated sheets
What must membrane proteins have to generate a rest pot?
Specific proteins localized to soma, dendrites, axon (specific proteins at specific locations)
How much current flows depends on these two things
- Electric potential (voltage V)
2. electrical conductance
What is the equilibrium potential for Ca2+?
123 mV
The potential difference that balances the ionic concentration gradient for any given ion (the voltage that balances diffusion)
Ionic equilibrium potential
Changing the concentration of this outside can cause the cell to depolarize, application seen in lethal injections
K
What do excitable cells have at rest?
A resting membrane potential which is negative (inside compared to out)
What three things are involved in generating a resting potential?
Cytosol and extracellular fluid, plasma membrane, and membrane proteins
How does a cell develop a rest pot?
Controlling what ions can move across the membrane
Something that stores charge
Capacitor
4 protein structures
primary, secondary, tertiary, and quaternary
How does rest. pot. vary between neurons? What does -65 represent?
Different types have different rest pots and -65 is the average
Forms barrier to water and ions and allows membrane potentials to form
Phospholipid bilayer
What produces large changes in membrane potential?
Tiny changes in ionic concentrations ( ~.00001 M)
Ions are surrounded by clouds of water called this in the cytosol and extracellular fluid
Spheres of hydration
A measure of the difference in charge between anode and cathode (force on particle), more difference = more current
Voltage
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)
What is the protein structure of many channels?
Quaternary
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
