Membrane Potential Generation Flashcards
Define resting ion channels.
Always open K+ channels, generate RMP, ‘leaky’ channels
Define gated channels.
Closed when membrane is at rest, regulated by changes in membrane potential, ligand binding or stretch
What generates an electrical potential?
Differences in specific concentrations of specific ions
Membranes are selectively permeable
Presence of active transporters
Specific types of ion channel
What type of ion lines the outer membrane?
Cloud of positive ions
What type of ion lines the inner membrane?
Thin cloud of negative ions
What calculation is used to define the membrane potential?
Vm = Vin - Vout
Vout is defined as zero
What are positive and negative ions called?
Cations (+ve)
Anions (-ve)
Define direction of current flow?
Direction of net movement of positive ions
What does a reduction of charge cause?
Depolarisation of the membrane - less negative
What does an increase of charge cause?
Hyperpolarization of the membrane potential - more negative
Define equilibrium potential?
The balance of electrical driving force and chemical driving force
What ions are found mostly extracellularly?
Sodium and Chloride
What ions are found mostly intracellularly?
Potassium
Define a membrane potential at rest.
Potential at which the flow of ions out (mostly K+) is equal to the flow of ions in (mostly Na+)
What maintains the membrane potential at rest?
Pumps eg. Na/KATPase
What creates a charge imbalance?
Ions moving down their electrical gradient which acts in opposition to the concentration gradient.
When is equilibrium potential achieved?
When the concentration forces are balanced by these electrical forces.
Why is RMP usually ~ -70mV?
Due to the high permeability of the membrane to K+ and small relative permeability of membrane to Na+
Define the Nernst Equation.
Ek = (RT/zF)ln([K+]0/[K+]i) = 58mV
Why do we use the Goldman Hodgkin-Katz equation?
In order to calculate the RMP, the permeabilities and concentrations of Na+, K+ and CL- must be considered
What does the equilibrium of the cell depend on when 7 ions are present?
The relative permeability of the ions
AT rest the permeabilities have the ratio PK:PNa:PCl = 1:0.03:0.1
What ratio is the RMP close to and why?
K equilibrium potential as PK dominates
What happens to the membrane potential during an action potential?
Membrane potential depolarises towards equilibrium potential for Na+ ions
What are the differences between membrane potential and equilibrium potential?
Vm is a steady state and represents a synthesis of all these forces but it is not equilibrium.
Eq is an equilibrium potential
