What is a membrane potential?
The electrical potential difference across the plasma membrane of ALL cells
How is the resting potential of a cell measured?
Using a very fine glass micropipette called a microelectrode to penetrate the cell membrane
The micropipette is filled with conducting solution
What are the range of values for resting potentials of animal cells?
-20mV to -90mV
The resting membrane potentials are largest in which cells?
Skeletal muscle and cardiac muscle (-80mV to -95mV)
What is the range of nerve cell resting potential?
-50mV to -75mV
Explain the concept of selective permeability
The resting membrane can be selectively permeable to ions, based on the types of ion channel proteins that are in the membrane and whether gated channels are open or not
How does selective permeability of cell membranes arise?
Through channel proteins present in the cell membrane which allow some ions to permeate. They are characterised by selectivity, gating and a high rate of ion flow down the electrochemical gradient for the ion
How is the resting potential set up given the distribution of ions across cell membrane?
At rest, the a typical mammalian cell has open K+ channels, so is selectively permeable to K+. Since anions cannot follow, the cell becomes negatively charged inside with the generation of an electrical gradient
What is the “equilibrium potential for an ion”?
The electrical and chemical gradients for K+ are equal and balance so there is no net driving force on K+ across the membrane
How would you calculate equilibrium potential for an ion from the ionic concentrations on either side of the plasma membrane?
Using the Nernst equation
What is depolarization?
What happens to the interior of the cell in relation to charge?
A decrease in the membrane potential, so that the inside of the cell becomes less negative
What is hyperpolarisation?
What happens to the interior of the cell in relation to charge?
An increase in the membrane potential, so that that the inside of the cell becomes more positive
Explain mechanisms that may lead to depolarisation
Opening Na+ or Ca2+ channels
Explain the mechanisms hat may lead to hyperpolarisation
Opening K+ or Cl- channels
Explain how changes in ion activity can lead to changes in the membrane potential
c
Outline some of the roles of the membrane potential in signalling within and between cells
c
Outline how ligand-gated channels can give rise to synaptic potentials
Synaptic potentials can be fast or slow depending on wether the receptor is also an ion channel, and depending on which ions the channels are selective for
What does increasing the membrane permeability for a particular ion do to the membrane potential for that ion?
Moves it towards the equilibrium potential
How do we deal with real membranes that are not perfectly selective for one ion species?
Use the Goldman-Hodgkin-Katz (GHK) equation
How do we deal with real membranes that are not perfectly selective for one ion species?
Use the Goldman-Hodgkin-Katz (GHK) equation
In fast synaptic transmission, the receptor is also what kind of channel?
What does this mean?
Ligand-gated ion channel
It has two functions:
1) It binds its related ligand (neurotransmitter)
2) It acts as an ion channel
Depolarising transmitters open channels with _______ reversal potentials, i.e. channels selective for what?
Na+, Ca2+
Do depolarising transmitters lead to excitatory or inhibitor postsynaptic potential?
Excitatory postsynaptic potential (EPSP)
Hyperpolarizing transmitters open channels with _______ reversal potentials i.e. channels selective for what?
K+ or Cl-
Do hyperpolarizing transmitters lead to excitatory or inhibitory postsynaptic potential?
Inhibitory postsynaptic potential (IPSP)
What is the difference between fast and slow synaptic transmission?
In fast synaptic transmission, the receptor itself is a ligand-gated ion channel whereas in slow synaptic transmission it is not itself an ion channel, but signals to the channel
Which two ways can the receptor in slow synaptic transmission signal to the channel?
Within the membrane -localised and rapid
Via an intracellular messenger - throughout the cell, amplified by cascade
What two other factors can influence membrane potential, apart from ion channels?
Changes in ion concentration Electrogenic pumps (e.g.NA/K ATPase)
