Membrane Potential Flashcards
What is the membrane potential of a cell? What is it measured in?
The magnitude of an electrical charge that exists across a plasma membrane?
Millivolts
Which type of cell has the lowest resting membrane potential?
Erythrocytes (-9mV)
How do you measure a membrane potential?
Two electrodes connected to a voltmeter
One electrode = microelectrode
Filled with conducting solution
Penetrates the plasma membrane?
What is a microelectrode? What is the diameter of its tip?
Fine glass pipette used to penetrate the plasma membrane to measure membrane potentials
1 micrometre
What type of channels dominate the membrane of a resting cell?
Open K+ channels
What does the equilibrium potential of an ion measure?
The voltage at which the electrical gradient and chemical gradient of an ion balance
What factors affect the resting membrane potential of a cell?
Permeability of the cells to each particular ion (e.g. No of channels for each ion)
What is depolarisation?
A decrease in the size of the membrane potential from its original value (e.g. -70mV to -30mV)
What is hyperpolarisation?
An increase in the size of the membrane potential over its original value (e.g. -70mV to -90mV)
An increase in permeability to an ion will move the membrane potential towards…
The equilibrium potential for that particular ion
What is the equilibrium potential for K+?
What is the equilibrium potential for Cl-?
- 95mV
- 96mV
What is the equilibrium potential for Na+?
What is the equilibrium potential for Ca2+?
+70mV
+122mV
Opening of _______/_______ channels causes depolarisation
Na+ and Ca2+ channels
Opening of K+/Cl- channels causes….
Hyperpolarisation
What is conductance?
Refers to the fact that the contribution of an ion to the membrane potential will depend on how permeable the membrane is to that ion
What ions do nicotinic ACh receptors transport?
Moves both Na+ and K+
Where in the body can you find mechanically gated channels?
Hair cells in the inner ear
What two types of synaptic transmission exist?
Fast and slow
What is fast synaptic transmission?
Where the receptor protein is also the ion channel? (E.g. Nicotinic ACh receptors)
At inhibitory synapses channels open that are permeable to…
K+ and Cl-
At excitatory synapses channels open that are permeable to…
Na+ and Ca2+
What is slow synaptic transmission?
Where the receptor protein and ion channel are separate proteins (e.g. GPCRs)
What is the contribution of the Na/K ATPase pump to the membrane potential
Minimal - contributes a few mV
What happens in the Beta-cells of the Islets of langerhans in response to increased glucose levels?
Increase ATP
ATP binds to ATP-sensitive K+ channels - closing them
[K+] in the cell increases
Membrane depolarisation
Calcium channels open, Ca into the cell, insulin released
What can sulphonylurea be used for?
To permanently close ATP-sensitive K+ channels
What specific properties do cardiac ion channels possess?
Each channel will only transport one type of ion
They are all voltage dependent
What is the resting potential in cardiomyocytes?
-90mV
When do calcium channels open in cardiomyocytes?
-40mV
