Nerves 2 Flashcards
what are the 3 main electrical potentials that exist?
- action potentials
- graded potentials
- resting membrane potentials
function of action potentials?
send long distance signals along the axon to a distant site
function of graded potentials?
decide WHEN an action potential should be fired and if it should be fired
function of resting membrane potential?
- keeps cells always ready to respond to stimulus
- occurs when neurones are sitting still (membrane potential is at rest)
what voltage does resting membrane potential sit at?
-70mV
is the cell at RMP (resting membrane potential) negative or positive compared to the outside?
negative (outside it’s 0mV)
If ion channels/ pores which are permeable to K only are added, in what direction will K move?
Out of the cell (down its concentration gradient) since it’s at high conc. intracellularly (high in ICF and low in ECF)
when is an equilibrium potential established? what is equilibrium potential?
membrane potential at which the electrical gradient is exactly equal and opposite to the concentration gradient
what will happen to equilibrium potential and electrical potential if concentration gradient is very high?
it will cause a BIGGER electrical potential and equilibrium potential will be HIGHER
what are the 3 terms which link together? (have a clear correlation?)
- equilibrium potential
- concentration gradient
- electrical gradient
Due to what part of the cell are cells at RMP?
due to leaky K channels which are always open at rest (permeable)
what is the role in equilibrium potential an concentration gradient in K movement?
- conc. gradient is pushing K out
- equilibrium potential/electrical gradient is drawing K back in
when is a big resting potential formed?
when there is a big conc. gradient and lot of K flows out of the cell
when is a small resting potential formed?
when there is a small conc. gradient and less K flows out of the cell
what determines equilibrium potential?
concentration gradient
what equation predicts equilibrium potential for a SINGLE ion species?
Nernst equation
what prevents high levels of K affecting our brain?
blood brain barrier
describe what happens when a banana is eaten (high in K)
- banana eaten and levels of K in ECF rise
- conc. gradient is reduced
- this sustains a smaller electrical gradient at equilibrium
- RMP is reduced/stops/decreased (cell depolarises)
what does blood brain barrier do?
protects the brain from changes in K concentration in the plasma. Heart does not have this mechanism
what structures are fundamental in blood brain barrier?
- tight capillaries
- astrocytes
- tight junctions in the endothelial cells
why is RMP at -70mV?
due to other leaky channels such as Na or Cl
where are concentrations of K high?
in ICF
where are concentrations of Na and Cl high
in ECF
Why do Na and Cl leaky channels have a smaller effect on RMP compared to K channels?
because their permeability is lower whereas RMP is close to K equilibrium
What does the Na/K pump establish?
concentration gradient
what equation predicts equilibrium potential generated by SEVERAL ions?
Goldman equation
what happens if more K channels are opened?
more K flows out and cell hyperpolarises (more negative)
what happens if more Na channels are opened?
more Na flows in and cell depolarises (more positive)
what happens if more Cl channels are opened?
more Cl flows in and cell hyperpolarises (more negative)
what happens if more Ca channels are opened?
more Ca will flow in and cell depolarises (more positive)
what is the special characteristic of Ca ions?
they can travel in both directions
is Ca involved in RMP?
no, not at all
what happens to cell at depolarisation
becomes more POSITIVE ( mV approaches 0)
what happens to cell at hyperpolarisation?
becomes more NEGATIVE (mV goes below RMP)
what happens to cell at overshoot?
mV goes way above 0mV
what happens to cell at repolarising?
cell’s mV travels from overshoot back down to RMP
if K travels into the cell naturally (2Kin) why is it moving out?
due to concentration gradient (moves down/ along it), from high conc. in ICF to low conc. in ECF)
