Membrane Potential Flashcards
What is the range of values of resting membrane potential in animal cells?
-20 to -90 mV
Nerve cells: -50 to -75
Smooth muscle cells: approx -50
Cardiac and skeletal muscle: -80 to -90
What is a Resting Membrane Potential?
The potential inside of the cell relative to the extracellular solution.
All cells have an electrical potential difference across the membrane, provides the basis of signalling in the NS
How is the resting potential set up?
For most cells, K channels dominate the membrane ionic permeability at rest.
When the chemical and electrical gradients for K are equal and opposite there will be no net movement but there will be a negative membrane potential, the RMP arises because the membrane is selectively permeable to K
What is an equilibrium potential?
The equilibrium potential for an ion is the membrane potential at which there is no net movement of that ion, ie. conc gradient=electrical gradient.
Calculated with the Nernst equation
Define depolarisation and explain the mechanism that leads to it
Membrane potential decreases in size (cell interior gets less negative).
May only be by a few mV, may not be an action potential.
Eg. opening Na or Ca channels
Define hyperpolarisation and explain the mechanism leading to it
Membrane potential increases in size, falls below resting (cell interior becomes more negative)
Eg. opening Cl or K channels
How can changes in ion channel activity lead to changes in membrane potential?
If the cell is made more permeable to a particular ion (by increased ion channel activity) then the membrane potential will move towards the equilibrium potential for that ion.
The contribution of each ion to membrane potential depends on the number of open channels for that ion.
What are the 3 ways that ion channels can be gated?
Ligand gating - channels respond to intra/extracellular messengers
Voltage gating - channels respond to changes in membrane potential
Mechanical gating - channels respond to membrane deformation eg mechanoreceptors
What is the difference between fast and slow synaptic transmission?
Fast synaptic transmission is where the receptor protein is also an ion channel.
In slow synaptic transmission the receptor protein and the ion channel are separate proteins
How is an Excitatory Post-Synaptic Potential brought about?
Excitatory transmitters (eg ACh, glutamate) open ligand gated ion channels permeable to Na/Ca and cause depolarisation of the membrane. Longer time course than an AP, graded by the amount of transmitter
How is an Inhibitory Post-Synaptic Potential brought about?
Inhibitory transmitters (eg glycine, gamma-aminobutyric acid=GABA) open ligand-gated channels permeable to K/Cl which causes hyperpolarisation. This decreases membrane excitability.
What are the 2 ways that slow synaptic transmission can occur?
By direct G-protein gating - via G-protein coupled receptors localised to a patch of membrane. Fairly rapid
By gating via intracellular messengers - protein kinase or 2nd messenger opens the channel after a signal cascade throughout the cell. Very slow
How would you measure membrane potential?
Use a voltmeter and a microelectrode (fine glass pipette), which penetrates the cell membrane, filled with a conducting solution.
What factors affect membrane potential other than the ion selectivity of the plasma membrane?
Changes in ion concentration extracellularly eg in hyperkalaemia
Electrogenic pumps directly contribute a few mV to the membrane potential
