Membrane Potential Flashcards
What is membrane potential?
Magnitude of an electrical charge that exists across a membrane and is always expressed as the potential inside the cell relative to the extracellular solution
What is membrane potential measured in?
mV (millivolts)
What is a humans membrane potential at rest?
-70mV
What do all animal cells have in common?
All animals have negative membrane potentials at rest
What does the electrical potential difference across a plasma membrane provide?
The basis of signalling in all types of cells
How can a membrane potential be measured?
Microelectrode (fine glass pipette) penetrates cell membrane and uses voltmeter to measure resting potential
What factors are important in the establishment of a membrane potential?
Asymmetric distribution of ions across the plasma membrane (concentration gradients)
Selective ion channels in plasma membrane (K+, Na+, Cl- are most important)
In english- concentration gradients and ion channels
Other than ions, what else effects the negative charge in a cell?
Proteins (increases negativity as more in cell than outside cell)
What happens if we have a non permeable membrane and no membrane proteins?
No movement of ions
What happens if we have a freely permeable membrane?
no charge on the membrane but movement of ions
What happens if we have a semi-permeable membrane?
charge seperation and an electrical gradient
If electrical and chemical gradients are equal for K+ what happens?
No net movement but is a negative charge across the membrane
What is the Nernst equation?
Allows you to calculate the membrane potential at which an ion will be in equilibrium, given the extracellular and intracellular concentrations
What does the charge of a cell depend on?
The abundance of different channels - if more Na or Ca will have smaller difference as -70mV rather than Cl and K with -95mV
What ion dominates the resting membrane permeability?
K+
What cells are close to Ek?
Nerve cells and Cardiac cells as many k channels
What cells have low resting membrane potentials as have less K channels?
Erythrocytes and smooth muscle cells
Why are skeletal muscles resting potential so high?
lots of Cl- and and K+ channels
What is depolarisation?
A decrease in size of the membrane potential from its normal value
Cell interior becomes less negative
-70 to -50mV
What is Hyperpolarisation?
An increase in the size of the membrane potential from it normal value
Cell interior becomes more negative
-70mV to -90mV
What does opening K+ or Cl- channels do?
Cause hyperpolarisation
What does opening Na or Ca channels do?
Cause depolarisation
What is conductance?
The contribution of each ion to the membrane potential will depend on how permeable the membrane is to that ion
How are Nicotinic acetyl choline receptors opened?
By binding of 2 ACh
