lecture 4 - action potential properties _ voltage clamps

types of voltage gated ion channels

Na+ channels

K+ channels

Ca2+ channels

membrane potential

separation of charges across membrane

current

movement of ions across membrane

how to keep Na+ out

it is not very permeable and whatever leaks in will be pumped back out

components of an AP

threshold

upstroke

downstroke

afterhyperpolarization

absolute refractory period

relative refractory period

hodgkin and huxley (3 findings)

activation of voltage gated Na+ channels

inactivation of Na+ channels

delayed activation of K+ channels

what did hodgkin and huxley experiment on

giant squid axon

what idd hodgkin and huxley find that led to their findings

early inward current and delayed outward current when the membrane is depolarized

after adding TTX which blocks voltage gated Na+ channels, early current blocked so early current due to sodium influx

TEA blocks late current so late current is bc of K+ channels

what causes depolarization

Na+ channels

what causes repolarization

K+ channels

what causes afterhyperpolarization

K+ efflux

what brings back to resting potential

closing of K+ channels

inactivation

the sodium channels close even though the neuron is depolarized

deactivation

the sodium channels shut off; requires membrane hyperpolarization

absolute refractory period

when na+ channels are inactivated - peak to resting potential

impossibel to generate another action potential

relative refractory period

after na channels recover from inactivation but while K+ channels are open and cell is hyperpolarized

more stimulus than normal needed but AP possible

what ensures one way propagation of action potential

absolute RP

what important characteristics of neural activity are refractory periods responsible for

frequency based on stimulus intensity

what proportion of ions flow during an AP

very small, so a single AP has little effect on relative concetrations of various ions