Excitable Cells Flashcards
(45 cards)
action potential
rapid change in membrane potential
Resting membrane potential
slight negative charge inside cell
around -70mv
k+ leak channel
k+ moves down concentration gradient
outside of membrane becomes slightly positive
Na+ leak channel
Na+ moves down conc. grad. into cell
immediately removed by sodium potassium ATPase
equilibrium potential potassium
potassium stops moving when electrical gradient equal and opposite to concentration gradient
-86mv
sodium Eq
+60mv
- resting state
both voltage gated channels are closed
- slow rising phase
sodium moves through voltage gated channel
- rapid rising phase
sodium potassium ATPase moves through voltage gated channels
- early repolarisation
balance cant be reached so sodium channels blocked
- hyperpolarisation
potassium moved back into cell, channels blocked
describe movement of sodium ions as action potential is generated
sodium ions enter cell, they would continue to do so until Eq is reached (+60) however channels inactivate at around +30 and block the ions from entering the cell
describe movement of potassium ions as action potential is generated
potassium ions continue to leave the cell even after repolarisation. Rmp tries to reach the potassium Eq (-86mv) but potassium channels inactivate before it can reach this point
How do voltage gated ion channels work?
activation gate is voltage dependent
inactivation gate is time dependent
open - inactivated - closed
absolute refractory period
membrane cannot generate another a.p. no matter how big the stimulus is
relative refractory period
membrane can generate another a.p if the stimulus is bigger than normal
where does the a.p. start?
axon hillock
how does axon diameter affect velocity of a.p.?
larger the diameter, the more room for local current flow in current loops
how does membrane resistance affect velocity of a.p.?
higher membrane resistance, less current lost by leaking as more current stays in current loops
multiple sclerosis
demyelination of axons so a.p. cannot jump between nodes of ranvier
gradual motor control loss
synaptic transmission
- a.p. invades axon terminal, presynaptic membrane depolarised
- depolarisation opens voltage gated Ca2+ channels
- Ca2+ rushes into axon terminal down conc. grad.
- rise in Ca2+ conc causes vesicles to fuse with presynaptic membrane
- vesicles release Ach into synaptic cleft (exocytosis)
- Ach molecules diffuse across cleft
- Ach molecules bind to receptors on postsynaptic membrane
- Ach molecules bind to receptor, ligand gated Na+ ion channels open
- Na+ rushes into postsynaptic cell, K+ leaves cell
postsynaptic MP is halfway between K+Eq and Na+Eq
ligand gated definition
opened by another molecule
e.g. ligand gated Na+ channels opened by Ach
end plate potential
halfway between Na+ Eq and K+Eq
-15mv
1 EPP
100 x mEPP
1 mEPP = 1 vesicle fusion
