The Resting Cell Membrane Flashcards
How is the membrane potential measured?
By micro electrode which is a fine glass pipette. It can penetrate the cell membrane and is filled with a conducting solution.
Define resting membrane potential.
The electrical charge that exists across a membrane like a plasma membrane or mitochondrial membrane. It is always expressed as the potential inside the cell relative to the extracellular solution. This means if the membrane potential is negative, the potential is negative inside the cell relative to the outside.
What is the normal range of resting potentials in the human body’s cells?
-20 to -90 mV
What is the resting potential in cardiac and skeletal muscle?
-80 to -90 mV.
What is the resting potential in nerve cells?
-50 to -75 mV. -70mV is the average value.
What is the resting potential in smooth muscle cells?
-50 mV.
What are the intracellular values of Na+, K+ and Cl-?
Na+ = 12mM K+ = 155mM Cl- = 4.2mM
What are the extracellular values of Na+, K+ and Cl-?
Na+ = 145 mM K+ = 4.5mM Cl- = 123 mM
What is the main cause of the resting potential?
The selective permeability to K+. When the chemical gradient and electrical gradient of K+ are equal there will be no net movement of K+ and there will be a negative membrane potential.
In what direction is the chemical gradient for K+ at resting potential?
Outwards. Since K+ intracellularly is 155mM and extracellularly 4.5mM chemically K+ will go out of the cell.
In what direction is the electrical gradient for K+ at resting potential?
K+ want to go into the cell. This is because the membrane potential is negative.
What is the equilibrium potential?
Theorising of a membrane perfectly selectively permeable to one ion. When the electrical gradient and chemical gradient are equal this is the equilibrium potential. This means there is no net movement of the ion either in or out of the cell.
The equilibrium constant for K+ is -95mV but that is not the case for any of the cells. Why?
Because cells’ membrane are not only permeable to K+ but also other ions. Normally Na+ and Ca2+ transporters are closed but they can flicker. This will increase the membrane potential to somewhere around -70mV.
Smooth muscle cells have a resting potential at -50mV. What does this mean regarding the equilibrium potential K+?
It means that the membrane is not as selective for K+. There is an increased contribution of other channels.
