M&R S3 - The Resting Membrane Potential Flashcards
Can a membrane potential be found in all types of cells?
Yup
What is the resting membrane potential?
The potential inside the cell relative to the outside
Describe the range of resting membrane potentials seen in animal cells
Animal cells have membrane potentials from -20mV to -90mV
Nerve cells = -50 to -75mV
Smooth muscle cells = -50mV
Cardiac and skeletal muscle = -80 to -90mV
How can membrane potential be measured?
A micro-electrode:
Fine glass pipette
Penetrates into the cell
Filled with conducting solution (KCL)
Tip diameter is 1um
Another electrode is placed in the surrounding fluid and a voltmeter used to identify difference in potential across the membrane
How is the membrane potential created and controlled?
Selective permeability of membrane to ions through utilisation of transport and channel proteins
These proteins can be gated to allow control of the ion levels intracellularly
See Session 2 for more detail
What is the intra and extra-cellular concentration of: Na+ K+ Cl- Other Anions
Na+:
Intra- 10mM
Extra - 145mM
K+:
Intra - 160mM
Extra- 4.5mM
Cl-:
Intra - 3mM
Extra - 114mM
A- (Other Anions):
Intra - 167mM
Extra - 40mM
How is the resting membrane potential created?
At rest the membrane has open K+ channels,
K+ diffuses out As Anions cannot follow, the cell becomes negatively charged
The movement of K+ ions out of the cell is opposed by the electrical gradient (they are moving up the gradient).
When electrical and chemical gradients exert the same force on K+ ions the resting potential has been reached
Define ‘Equilibrium potential’ in terms of ions
The membrane potential at which there is no net movement of that ion across the membrane
Concentration gradient = Electrical gradient
What is the Nernst equation?
Hint: Assume 37 degrees celsius
Ions in = concentration of ions inside the cell
Ions out = Concentration of ions outside the cell
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Give a brief description of membrane depolarisation
Provide an example of how this might come about
Membrane potential decreases in size towards 0
May only be by a few millivolts, not necessarily an action potential
Cell interior becomes less negative
This could come about by the opening of Na+ or Ca2+ channels
Give a brief description of membrane hyperpolarisation
Provide an example of how this may come about
Membrane potential increases in size
Potential falls below resting
Cell interior becomes more negative
This could come about by the opening of K+ or Cl- channels
Which type of channel dominates the resting permeability of a cell?
Why is the resting potential not equal to the equilibrium potential for this ion?
K+ channels are predominantly open at rest
Resting potential is higher than equilibrium potential -70mV vs -95mV)
Tjis is because other types of channel are also open
What effect will changing the equilibrium potential of K+ ions have on a cells resting potential?
Why?
Will change the resting potential in the same direction as the change in equilibrium potential for K+
Resting potential is predominantely influenced by K+ permeability/equilibrium potential
Explain what is calculated by the Goldman-Hodgkin-Katz equation
Write out the equation, explain the meaning of any symbols present
The GHK equation provides a good approximation of membrane potential as determined by Na+, K+ and Cl- ions
Vm = Membrane potential
PNa PK PCl = Relative permeabilities of the ions
[ion] = concentration of the ion
R = Gas constant
T = Temperature (celsius)
F = Faraday’s number
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What are the two types of channel gating?
Give a brief description of each type
Ligand Gating:
Channel is opened or closed by binding of a chemical ligand which may be an intra or extra cellular messenger
Voltage Gating:
The channel opens or closes in response to changes in the membrane potential
Where types of cells are synaptic connections found between?
What are the two types of synaptic transmission?
Synaptic transmission occurs between nerve, muscle, sensory cells and glands
Fast and slow synaptic transmission
What is the distinction between fast and slow synaptic transmission?
Fast:
The receptor proteins is also an ion channel, the binding of neurotransmitter causes the channel to open
Slow:
The receptor protein and ion channel are separate proteins.
What is are the patterns of slow synaptic transmission?
Provide a brief explanation of each
Direct G-protein gating:
Receptor is directly linked to the ion channel by G protein
This process is localised and quite rapid
Gating via intracellular messenger:
G-protein linked receptor activates an enzyme, iniatiating a signalling cascade resulting in the opening of the ion channel
This activation occurs throughout the cell
Describe the action of Excitatory synapses
Hint: Channels, Potential change
Excitatory transmitters open ligand gated channels, this causes membrane depolarisation
Transmitters include Acetylcholine, Glutamate
Graded with the amount of transmitter
Can be permeable to Na+, Ca2+ or cations in general
Results in an Excitatory Post Synaptic Potential (EPSP)
Has a longer time course than an action potential
Describe the action of inhibitory synapses
Hint: Channels, Potential change
Inhibitory transmitters open ligand gated channels, this causes membrane hyperpolarisation
Transmitters include Glycine, GABA
Graded with the amount of transmitter
Permeable to K+ or Cl-
Results in an Inhibitory Post Synaptic Potential (IPSP)
Has a longer time course than an action potential