Unit1Lec 2-The Membrane Potential Flashcards
Membranes consist of?
- Phospholipids
- Proteins
Function of Phospholipid bilayer
- Acts a barrier to many solutes
- Makes a seperation b/n the extra-cellular and intra-cellular environment
Function of Transmembrane proteins
- Provides permeation pathway
- Acts a sensors that relay pathways
Transmembrane protein function and regulation is the essence of what three factors?
- Cellular communication
- Changing cellular fxn by controlling what goes into and out of cell
- Events that occur inside cell
List the 3 mechanism that transport across the membrane occurs
- Diffusion
- Carrier Proteins
- Ion Channels
Explain Diffusion mechanism
Solute or small species can simply diffuse through the plasma membrane
Explain Carrier Protein mechanism
Proteins that provide help for solutes to cross the plasma membrane b/c they are too big or charged
Explain Ion Channel mechanism
Channels formed by some of the protein in the lipid bilayer, and form a water soluble channel that provides an environment for ions like Na+, K+, Cl- and Ca2+ to move from inside the cell to outside and vice versa
What type of molecules can cross the plasma membrane easily?
Only small, lipophilic molecules
What helps ions and larger molecules cross the membrane?
- Ion channels
- Transporters
Ion channels vs transporters
- Ion channels: provide a continous aqueous space for ions to move
- Transporters: Have a receptor to bind; binding causes a confirmation change that opens up to the other side. Then looses affinity to release it.
- Ion channels are quicker than transporters
List the major classes of ion channel
- Leak
- Stretch-activated
- Ligand-gated
- Voltage-gated
Explain Leak ion channels
Constitutively active channels
Maintains the resting membrane potential of the cell
Explain Streched-activated ion channels
LOW yield
When the plasma membrane is stretched, channel is activated
Explain Ligand-gated ion channels
A molecule (i.e. neurotransmitter) binds to a protein to activate a channel
Explain voltage-gated ion channels
Channel activates following a change in membrane potential
Why does a voltage difference exists across the plasma membrane?
In resting state the inside of a cell is more negatively charged than its outside positively charged environment (charged gradient)
What is the voltage difference across the membrane called?
Membrane potential= Em or Vm
What creates the membrane potential (Em)?
Different ions concentrations across the plasma membrane, and selective permeabilites of those ions,resulting in a charged gradient
Explain action potential
Trasient changes in membrane potential caused by the orchestrated opening and closing of ions cells
At rest what is the membrane potential of neurons?
-70 mV
Describe the mechanism of the activation of a action potential for a nueronal cell
At rest: -70 mV–>action potential causes depolarization (- to +)–>Repolarization quickly occurs after (+ to -)—>then hyperpolarization happens (past -70 mV)
Explain the equilibrium (nerst) potential (Eeq)
HIGH yield
- Reflects a balance (at equilbrium) between the chemical gradient and electrical gradients for a single permeable ion
What is the Nerst Equation?
HIGH yield
Eeq=58/z*log(co/ci)
z=ion charge
ci=internal concentration
co=external concentration
What determines the direction an ion moves?
Knowing the equilibriun and membrane potential for that ion
Where does membrane potential always want to go?
Towards equilibrium
If Em is less than Eeq what is the movement for a cation (+)?
Moves IN the cell
If Em is more than Eeq what is the movement for a cation (+)?
Moves OUT the cell
if Em is less than Eeq what is the movement for a anion(-)?
Moves OUT of the cell
if Em is more than Eeq what is the movement for a anion(-)?
Moves IN the cell
What determines the neuronal resting membrane potential?
The permeabilities and concentrations of Na+, K+, and Cl
What is the concentration of Na+, K+, and Cl- inside and outside the cell at Em=-70mV?
Equilibrium potential
- Inside: 10 Na+, 30 Cl-, 140 K+
- Outside: 145 Na+, 110 Cl-, 5K+
What is the membrane potential of Na+ for a resting neuron?
HIGH yield
E(Na+)=+67 mV
What is the membrane potential of Cl- for a resting neuron?
HIGH yield
E(Cl-)=-33 mV
What is the membrane potential of K+ for a resting neuron?
E(K+)= -84 mV
What is used to calculate membrane potential?
The Goldman Equation
Explain the Goldman Equation
Describes the resting membrane potential accounting for relative permeabilites, and concentration gradients of the three primary permeable ions
What is the Goldman Equation
Em=58log{(PK[Ko+]+PNa[Nao+]+PCl[Cli-])/(PK[Ki+]+PNa[Nai+]+PCl[Clo-])}
List the 2 mechanisms that Em can be changed by?
- changing internal/external ionic concentrations (primarly K+)
- changing the relative permeability of the ions across the plasma membrane
What ion is the resting mammalian neuron most permeable to and why?
K+, thus Em is closest to the equilibrium potential of K+
Resting potential= -70mV
EK+= -87 mV
As external [K+] increase, Em becomes…..
Less negative (depolarization)
As external [K+] decreases, Em becomes….
More negative (hyperpolarization)
What occurs to Em when an ion increases permeability?
Em moves toward the equilbrium potential of the ion with increased permeability
- Which of the following ions would cause the most substantial change in resting membrane potential (Em) if its external concentrations were increased?
A. Na+
B. Cl-
C. Ca2+
D. K+
d. K+
