3 The Resting Membrane Potential Flashcards
How is a membrane potential expressed?
The potential inside the cell relative to the extracellular solution. Given in millivolts (mV).
Describe a way of measuring membrane potential in a cell
Penetrate the cell membrane with a microelectrode filled with a conducting solution (KCl) which is attached to a voltmeter.
How is the resting potential set up?
The resting potential is maintained by the permeability of the membrane to ions.
Explain K+’s role in maintaining the resting potential.
K+ channels are mainly open so K+ moves OUT of the cell via a chemical diffusion gradient but also moves IN to the cell via an electrical gradient. When these are equal there will be no net movement.
What is the function of the Nernst Equation?
The equation allows the membrane potential at which K+ will be at equilibrium (given the current concentrations of K+), to be calculated.
What is the Nernst equation (at 37 degrees)
Ek= 61 x log10 [K+]o
— ——-
z [K+]i
Why is the Ek not the equilibrium potential for the whole cell?
A cell will be permeable to more than just K+ ions.
What is the approximate resting potential for cardiac muscle?
-80mV
What is the approximate resting potential for nerve cells?
-70mV
What is the approximate resting potential for smooth muscle cells?
-50mV
What is the approximate resting potential for skeletal muscle?
-90mV
Why are changes in membrane potential important in a cell? (4)
Action potentials
Triggering muscle contraction
Control of hormone and neurotransmitter secretion
Transduction of sensory information
Define ‘depolarisation’
A decrease in the size of the membrane potential from its normal value. Cell interior becomes less negative.
Define ‘hyperpolarisation’
an increase in the size of the membrane potential from its normal value. Cell interior becomes more negative.
Describe and explain fast synaptic transmission
The receptor protein is also an ion channel. Transmitter binding causes the channel to open. Excitatory transmitters open ligand-gated channels that cause membrane depolarisation. This results in an excitatory post synaptic potential (EPSP). They are small and long-lasting.
