membrane potential

membrane potential becoming MORE NEGATIVE.

ex: -70mV to -90mV

the opposition to flow. How difficult it is for ions to flow

g=1/R  where R is resistance

It is the measure ofhow easy it is for current flow to occur (ions to move through channel)

1. open an ion channel
2. inc. conductance
3. dec. resistance
4. inc. current flow
5. inc. permeability

• more Na outside cell
• more K inside cell
• Cell is more permeable to K than it is to Na
• Cl is mainly in extracellular fluid

Cations (+): Na and K

Anions (-): A- and Cl-

** A- is actually a (-) protein and an organic anion.

the total # of ions inside and outside is roughly equal (total of + and -)

Although there is a difference in charge at membrane (inside is (-) and outside is (+)) overall in/out side of the cell is roughly equal

ATPase actively transports Na out of cell and K into cell. at the same time, K passively exits via channel and Na passively enters via a channel

*** 50% of ATP in brain is used to drive ATPase, critical

1. ATPase pump is electrogenic
2. more K leaves the cell than Na coming in b/c K has greater permeability
3. A- is main negative charge inside membrane impermeable to A- so its stuck in cell keeping it negative

is only true if 1 ion is present.

gives you electrical potential needed to exactly oppose conc. gradient

gives the electrical potential diference neccesary for a specific ion to be at equilibrium

E_c = 61/z X log(conc. outside/conc. inside)

where z= charge of ion

log 10= 1

log 1= 0

log 0.1= -1

E_Cl =61/-1 log(100/10) = -61mV

*to figure out membrane potential ignore Cl- b/c its same as Vm= -60 to -70mV

Real cell: conc grad is out and its strongerthan the elecrial grad is in. so net K+ movement is out of cell.

so its -70mV b/c -70 is not as strong as -90 b/c conc grad has to win. At -90 you have equilibrium

Normal cell: conc. grad of Na+ is into cell and the electrical grad is into cell, sine both gradients are directed in, there is a high driving force for Na in. Na has low permeability. if an Na+ channel opens it increases permiability and causes influx of Na+

-70mV

why?

it sits nearer K+ b/c potassium has a high permeability

-90mV

BUT since some Na+ is moving in its -70mV the Na+ depolarizes the cell

K+: E _K+ is -90mV, [] grad goes OUT, electrical grad goes IN

Na+: E_Na+ is +60mV, [] grad goes IN, electrical grad is OUT

K+: is -70mV, [] grad is OUT, electrical grad is IN

Na+: is -70mV, [] grad is IN, electrical grad is IN

K+ [] grad wins and NET potassium movement is OUT

Net movement Na is into cell

more potassium out doe to high permeability

open Na channels and an influx of Na will occur

used to calculate actual membrane poential

• takes all major ions into account
• Cl is a (-) charge so it is flipped, inside/outside
• accounts for ion permeability

Vm(membrane potential)= NET K= into cell, NET Na into cell

E_K+ =61/1 log150/150= 0, the Vm is always between E_K+ and E_Na+ therefore answers:

• Vm between 0 and +61mV
• membrane potential depolarizes
• membrane potential is positive

NO [] grad for K+, electrical grad is OUT= NET movement OUT

[] grad is stronger for Na= Na in