Lecture 7- Resting Potentials Flashcards
how can the membrane potential be measured
- Use voltmeter and microelectrode inside and outside the cell - When both electrodes on the outside- voltmeter= 0 - When the microelectrode penetrates inside the cell the potential will be negative
phospholipid bilayer are permeable to
small uncharged molecules and very impermeable to charged ions
what changes the permeability of the phospholipid bilahyer
membrane proteins e.g. protein channels that enable ions to cross the cell membrane
membrane potential is defined as
the electrical charge that exists across a membrane
units of membrane potential
mV
resting membrane potential range from
-20 to -90mV
skeletal muscle resting potential
-90mV
cardiomyocytes resting potential
-80mV
nerve cells resting potential
-70mV
smooth muscle resting potential
-50mV
ion channels make the whole membrane
selectively permeable to ions
which channels dominate the membrane ionic permeability at rest
potassium
when do sodium channels open
during depolarisation
resting potential =
equilibrium potnetial of potassium (EK)
how is the equilibrium potnetial of potassium (resting potential) set up?
Chemical diffusion and electrical gradients
1) Chemical diffusion: Potassium flows out of the cell down its concentration gradient via diffusion
2) Electrical gradient: causes potassium to flow back in due to the negativity created by K+ initially leaving the cell down its conc gradient (and also intracellular anions)
When these forces are equal and opposite- no net movement of potassium - negative membrane potential due to anions
the Nerst equation can rearranged to
calculate the membrane potential at which [K+] ([any ion]) will be in equilibrium, given the outside and inside K+
resting potential of potassum
potassum dominates resting membrane permea bility
Ek= -95mV
Why is the resting ptoential of a cell - 70mV and not -95mV
Sodium and calcium channels leak sodium and calcium into the cell, diminishing the negative potential to -70mV
- Na+ and K+ channels normally closed- voltage sensitive
- Occasionally flicker into open conformation and then close again
- Depolarising the membrane
why do different cell types have different resting potnetials
In some cells the number of sodium, calcium and chloride (would make more negative)channels are higher or lower- different cells have different resting potentials e.g. smooth muscle cells must have lots of sodium and calcium channels
Na/K ATPase and resting potential
K + channels dominate the resting membrane permeability (not the Na/K+ ATPase)
Leaves negative potential inside cell- but only a tiny change
*predominant potential set by channels and not ATPase*
Role of Na/K+ ATPase
Leaves negative potential inside cell- but only a tiny change
Creates gradient for sodium and potassium to cause movement of ion
