Session 4 Flashcards
What are the resting membrane potential A) cardiac myocytes B)neurones C)Skeletal muscle myocytes D) Smooth muscle myocytes
A) -80mv
B)-70mv
C)-90mv
D)-50mv
Outline what a membrane potential is
Is the difference in electric potential between the inside and outside of the cell.
Negative under resting conditions
Positive during an action potential
How is the resting potential of a cell measured and the range of values found?
To measure the membrane potential you use a fine micropipette as a micro electrode that can penetrate the cell membrane and is filled with a conducting solution.
Expressed as voltage of inside the cell relative to the outside.
Explain the concept of selective permeability, and how the selective permeability of cell membrane arises
The membrane is is selectively permeable to different ions ( allows some through and blocks others).
It arises from ions channels that are:
1) Selectivity: channels only allow one or few ions through. (Na+, K+, Ca2+, Cl-)
2) Gating: Channels open/closed by conformational change in protein molecule
3)High rate of ion flow due to electrochemical gradient of the ion.
Describe how the resting potential is set up in terms of the electrochemical gradient and name the ion that predominates in this
1) K+ moves out of the cell down it’s conc gradient. Due to the Na+/k+ ATPase creating the conc gradient
2) Leaves the cell, becomes less positive and then K+ gets attracted back into the cell via the electrical gradient.
3) The two opposing gradients will reach an equilibrium potential for Potassium.
4) At resting potential most K+ channels are open
5) Na+ needs a threshold potential.
6) Resting membrane potential closest to the K+
Explain the term equilibrium potential for an ion.
For each ion the equilibrium potential is where the net flow through any open channels is O due to the Electrical chemical difference exactly balancing the concentration gradient.
How to calculate the equilibrium potential from the ionic concentrations on either side of the plasma membrane
It’s 61 divided by Z multiplied by log 10 that multiplied by (conc in divided the conc out) E ion = z 61 log10 [ion]in [ion]out
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The actual membrane potential of a nerve cell, when measured with a microelectrode was found to be -75mv. Why was the measured membrane potential different to that calculated for Ek?
There is leakage of sodium+ calcium due to spontaneous flickering across the cell membrane that is depolarising the gradient slightly
Define depolarisation and which channels are responsible
A decrease in the membrane potential so the inside of the cell becomes more positive. (Less negative)
Opening Na+/Ca2+ channels will depolarise cells
Define hyperpolarisation and the ion channels responsible for it
An increase in the membrane potential, so the inside of the cell becomes more negative.
Opening K+ or Cl- channels will hyperpolarize cells
Repolarisation
An increase in the membrane potential, so that the inside of the cell becomes less positive
Explain how the changes in ion channel activity leads to changes in membrane potential
The number of open channels of different underlies the overall selectivity of the cell membrane.
The amount of ion channels open and the different types of ion channels open causes a change in membrane potential
Outline some of the roles of the membrane potential in signalling within and between cells
Changing the number of open ion channels provides a way to control the cell’s membrane potential and produce signals.
1) If more potassium channels open- more k+ ions cross cell membrane, membrane hyperpolarizes, getting closer to the potassium equilibrium potential
2) If more Na+ channels open, more Na+ cross the membrane, cell would depolarise toward the sodium equilibrium potential.
Where does the resting membrane potential come from?
Is determined by the uneven distribution of ions between the inside and the outside of the cell and by the different permeability of the membrane to different types of ions
