Origin of membrane potentials Flashcards
not finished
Membrane potential (Em)
separation of opposite charges across the membrane
what does potential mean?
the ability to do work
What actually is Em? if not a charged membrane?
The difference in charge in the extracellular fluid and intracellular fluid
Which cells are excitable cells?
nerve and muscle cells
What do excitable cells do?
rapidly and transiently alter their permeability in response to appropriate stimulation, results in Em fluctuations
Resting membrane potential
Cells at rest, constant in non-excitable cells
What causes resting membrane potential?
unequal distribution of ions with selective movement through the membrane.
What Ions are unequally distributed? and where?
Na+ is higher outside the cell, gradient is inwards
K+ is higher outside the cell, gradient is outwards
Which ion has a leak channel?
both, but potassium has a greater amount
Are Na+ and K+ cations or anions?
cations
Which Ion is the membrane impermeable to?
negatively charged intracellular proteins
Equilibrium potential
When the concentration gradient and electrical gradient of an ion balance out, no net movement
Membrane potential at Ek
-90mV
Membrane potential at ENa
+60mV
Nernst equation
Eion=61log10 [ion0]/ [ion1]
K+ and Na+ effects on resting membrane
Cell is negative at rest ~ -70mV
relatively large net diffusion of K+ outwards
relatively small net diffusion of Na+ inward - neutralises some of the potential created by K+ alone
Goldman-Hodgkin-Katz (GHK) Equation
Em=61log10 (PK+[K+]0 + PNa+[Na+]0)/(PK+[K+]i + PNa+[Na+]i)
When Pk+ =1 in the GHK equation, what dies PNa+ equal?
0.01
What Em value do you use to plug in values for ion concentration
-83mV
Sodium potassium pump
maintains concentration gradients
3 sodium out for every 2 potassium in
generates hyperpolarizing current (inside is more negatively charged)
