Flashcards in Physiology 4 - Origins of membrane potential Deck (25)
What is the membrane potential? (Em)Units?
Separation of opposite charges across the membranemV (the membrane itself is not charged)
In terms of membrane potentials, what do excitable cells (e.g. nerve and muscle) have the ability to do?
Produce rapid, transient changes in their membrane potential when excited e.g. action potentials
What is the is the resting membrane potential?
Constant in non-excitable cells and in excitable cells at rest
What is the membrane potential due to?
Difference in the concentration and permeability of key ions
Extracellular and intracellular concentration of Na+?Concentration gradient
E = 150I = 15Inward
Extracellular and intracellular concentration of K+?Concentration outward?
E = 5I = 150Outward
Relative permeability of sodium and potassium?
Na+ = 1K+ = 100
Is the plasma membrane permeable to the large relatively negatively charged (anionic) intracellular proteins?
No - it is impermeable to these
Is the inside or outside of the cell more negatively charged?
Is the electrical gradient for K+ inwards or outwards?Is the concentration gradient for K+ inwards or outwards?
What is the equilibrium point?
The point where there is no net movement of charge (when the concentration gradient and electrical gradient balance each other out)
What is the equilibrium point for K+?
What does the negative sign before the equilibrium potential for K+ mean?
The polarity of the excess charge is on the inside of the membrane
What can be calculated using the Nernst equation?
The equilibrium potential for any given ion
What is the Nerst equation for a monovalent ion at 37 degrees?
Eion = 61log10([ion]o/[ion]i)
Direction of electrical and concentration gradient for Na+?
What is the equilibrium potential for Na+?
What effect does permeability for a given ion have on its tendency to drive membrane potential towards its own 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
What effect does concurrent K+ and Na+ movement have on establishing the resting Em?Resting membrane potential
Relatively large net diffusion of K+ outward (higher permeability)Relatively small net diffusion of Na+ inward neutralised some of the potential created by K+ aloneResting membrane potential therefore = -70mV
What can be used to calculate Em?
The Goldman-Hodgkin-Katz equation
What is the Goldman-Hodgkin-Katz equation?
Em=61log10((PK+[K+]0 + PNa+[Na+]0) / (PK+[K+]i + PNa+[Na+]i))
What does hyper polarisation mean?
a change in a cell's membrane potential that makes it more negative
What type of current does the Na+K+ATPase pump generate?
A hyper polarising current
What does depolarisation mean?
Making it more positive