Lecture 2/3- membrane potentials & action potentials Flashcards
How is the direction of current flow described?
the direction of net movement of positive ions
What is the resting membrane potential?
- The difference in voltage between the inside and outside of the cell as measured across the membrane
- -70mv
At rest, what ion is the membrane impermeable to?
Na+ ions
at rest, how are different ions and non-diffusible molecules (eg proteins) distributed?
- Extra cellular - high Na+ and Cl-
- intracellular - high K+ and proteins (with negatively charged side chains)
How is the RMP established?
- Na+K+ ATPase pump - sets up concentration gradients, pumps 3 Na+ out of cell and 2 K+ into cell as it hydrolyses ATP - just with this pump we already have a more (+) outside and (-) inside
- K+ leak channels - At RMP there is an increase of permeability to K+ than Na+ - more leak channels, Leak channels pump K+ out of cell which increases (-) charge in inside
What is a graded potential?
- changes in membrane potential
- no threshold or refractory period
- involves ligand/ mechanically gated ion channels
- signaling over short distances
Give examples of a graded potential?
- receptor potential (sensory receptors eg hair cells )
- Pacemaker potentials (eg SA node in right atrium)
- Synaptic potential
What is the Nernst equation used to calculate?
- it is used to calculate the equilibrium potential for 1 ion
What is the Goldmann equation used to calculate?
- it calculates the resting membrane potential, the permeabilities of the ions and the concentrations of the ions
- eg for Na+, K+ and Cl-
Why is the Goldmann equation and not the Nernst equation used to calculate RMP?
- this equation takes into account that not all ions are equally permeable to the membrane
- at rest, membrane is most permeable to K+ but there is also a small significant permeability to Cl- and K+
What is the equilibrium potential?
- the electrical potential that can balance the concentration difference across the membrane
- electrochemical equilibrium - conc of ion is evenly distributed
What is depolarisation?
- potential becomes less negative (more Na+ in cell)
What is repolarisation?
- When MP has been depolarised and it goes back to resting value - more (-) again
What is hyperpolarisation?
- When the potential is more (-) than the resting value
What is an action potential?
- large difference in membrane potential
- large depolarisation
- involves voltage gated ion channels eg Na+, K+ Ca2+ etc
- signaling over long distances
- only occurs in excitable cells eg neurons and muscles