M&R Session 3- The Resting Cell Membrane Flashcards
What is a resting membrane potential measured by?
A microelectrode that contains a conducting solution and penetrates the cell membrane.
What is a resting membrane potential?
It is the difference in potential across a plasma membrane.
What is the range of RMPs for animal cells?
-20mV to -90mV
What is the range of RMPs for cardiac and skeletal muscle?
-80mV to -90mV
What is the range of RMPs for nerve cells?
-50mV to -75mV
What is the most typical RMP for a nerve cell?
-70mV
How does membrane permeability arise?
The prescence of channels and transport proteins that span the membrane.
What equation can be used to find out the equilibrium potential for a particular ion?
The Nernst equation.
Why is the RMP often very close to the equilibrium potential for potassium?
Potassium channels are often open and therefore dominate the resting permeability.
Why is the RMP not exactly the equilibrium potential of potassium?
The membrane is not perfectly selective; it is leaky to other ions as it may have other ion channels present.
What happens to the membrane potential if you increase the permeability to a particular ion?
It will move closer to the equilibrium potential of that ion.
Define depolarisation. What happens to the cell interior?
A decrease in the membrane potential from its normal value.
The cell interior becomes less negative.
Define hyperpolarisation. What happens to the cell interior?
It is an increase in the membrane potential size from its normal value.
The cell interior becomes more negative.
Which two ions depolarise the RMP?
Calcium and sodium.
Which two ions hyperpolarise the RMP?
Potassium and chloride ions
What does the extend of ion contribution to the membrane potential depend upon? (2)
- the number of channels for that ion
- the permeability of the membrane for that ion
Which equation approximates what will happen to the membrane potential when all ions contributions have been taken into account?
The Goldman-Hodgkin-Katz equation
What is membrane selectivity determined by? (2)
- the number of channels open
- the number of channel types
What 3 ways are channels gated in?
- voltage gated
- ligand gated
- mechanically gated
What happens in fast synaptic transmission?
The receptors are also the ion channels.
Depolarising transmitters open positive channels and therefore cause an excitatory response- excitatory postsynaptic potential
Hyperpolarising transmitters open negative channels and therefore cause an inhibitory response- inhibitory postsynaptic potential
What happens in slow synaptic transmission?
The receptor isn’t the ion channel.
It signals to the channel either within the membrane via a G protein, or intracellularly using a G protein which then activates an enzyme that releases a messenger and activates the channel.
