Physiology Membrane Lecture 3 - The Resting Membrane Potential Flashcards
All plasma membranes of cells are polarised electrically which is know as membrane potential. What is membrane potential?
It is the separation of opposite charges across the membrane.
The difference in charge across a membrane (refers to the difference in charge between the thin layers of ECF and ICF located next to the inside and outside of the membrane, respectively)
The unequal distribution of ions and their selective movements through the plasma membrane.
What is Em?
Membrane potential
Is the plasma membrane charged?
Not charged
What are the units of membrane potential?
mV
What cells can produce a rapid, transient changes in their membrane potentials when excited (action potentials)?
Excitable cells e.g. nerve and muscle cells
What is meant by resting membrane potential?
This is the constant membrane potential in non-excitable cells and the membrane potential of excitable cells at rest.
What is the concentration gradient for K+ and Na+ directionally specking?
K+ is outward
Na+ is inward
K+ and Na+ are cations (positively charged). What is their electrical gradient towards?
Their electrical gradient is always towards the negatively charged side of the membrane!
Where is the concentration of Na+ and CL- highest?
In the extracellular fluid
Where is the concentration of K+ highest>
In the intracellular fluid because their are more leak channels for K+ than Na+. At resting potential the membrane is 100x more permeable to K+ than Na+
Why is the membrane 100x more permeable to K+ than Na+?
There are more leak channels for K+
What is meant by Ek or K+ equilibrium?
It is the equilibrium potential. The membrane of the cell initially has no charge. K+ will move down its concentration gradient to the outside of the cell leaving behind a negative charge. However, K+ will be attracted back into the negatively charged cell as it is positively charged. This tug of war will continue until the forces are balance. This is when the equilibrium is reached!
What are the two apposing forces acting on K+ in terms of plasma membrane?
- The concentration gradient (moving K+ out go the cell)
2. The electrical gradient (tending to move K+ into the cell)
When does no further net movement of K+ occur in terms of Plasma membrane?
No net movement is reached at equilibrium when the forces are balanced! (concentration gradient vs. electrical gradient)
What is the membrane potential for Ek?
-90mV
What is the Nernst equation?
It is the calculation of equilibrium potential for any given ion.
What is meant by ENa or Na+ equilibrium?
It is the equilibrium potential for Na+. At the beginning there is no membrane potential. There are more Na+ ions outside the cells so there is an inward movement of Na which causes a build up of positive charges inside the cell and leaves negative ions (mostly Cl-) outside the cell.
What can a greater permeability for a given ion do in terms of equilibrium potential?
The greater the permeability for a given ion, the greater the tendency for that ion to drive membrane potential towards the ion’s own equilibrium potential.
Are all cells negative or positive inside?
Negative
Why does membrane potential vary for different cell types?
Different cells have different permeability (for Na+ and K+ due to different number of leak channels)
What is the equilibrium potential (Em) for the membrane?
It is the potential for a membrane considering all other ions e.g Na+ and K+
What is Goldman-Hodgkin-Katz equation?
It is the equation used to calculate equilibrium potential considering all the ions.
What helps maintain the K+ and N+ gradients across the membrane?
Na+K+ pumps
What does hyperpolarizing mean?
The change in membrane potential making it more negative.
Why do Na+K+ pumps have a hyperpolarizing affect?
As every 3Na+ are exported, 2K+ are imported
Why does the amount of current change the Na+K+ pump add vary?
Different cell types have different pump activity and resistance of the membrane
What is the typical equilibrium potential for a resting cell?
Between -60mV and -85mV
What is the specialised use of Em in nerve and muscle cells?
Rapidly and transiently alter their membrane permeabilities in response to appropriate stimulation, resulting in fluctuations in Em.
Nerve impulses in nerve cells and triggering contraction in muscle cells - Changes in Em linked to secretion of insulin from pancreatic Beta-cells.
What accounts for the magnitude of the resting membrane potential?
The magnitude of K+ and Na+ concentration gradients, together with differences in permeability of the membrane to these ions.
At rest which is Em closer to, Ek or ENa?
Ek
