memrane potential and APs Flashcards
what factors determine how much current will flow
electrical potential: the force exerted on a charged particle and it reflects difference in charge between anode and cathode. (voltage
electrical conductance (g) the relative ability for charge to migrate from one point to another, measured in siemens g=1/R
Ohms law: I=gV or I=V/R
what is Eion and the nernst equation? and what is the driving force
Eion is the equilibrium potential; the electrical voltage that exaclty balances an ionic concentration gradient.
ionic driving force= Vm- Eion
Nernst equation: Eion=RT/Fz x ln [ion]o/[ion]i
where F is faraday constant and z is ionic charge
how much more permeable is the resting membrane to K than Na
40 times more permeable
how is the concentration gradient of the resting membrane maintained
Na/K ATPase pump
what is the goldman-hodgkin-katz equation
Em= RT/F ln (sum of permeability of ion x concentration of ion)/ sum of permeability of ion times concentration of ion)
for Na and K conc is o/i
for cl conc is i/o
what systems help maintain K+ gradient
blood brain barrier and astrocytes
what is the peak voltage of the AP
+40mV, RMP is -70mV
what is generator potential?
depolarisation by stimulus that may or may not cause an AP, if crossing threshold potential
what is difference between relative and absolute refractory period? what is theoretical maximum frequency?
absolute refractory period: lasts 1ms it occurs during repolarisation and immediately afterward, during this time no new APs can be generated because threshold is effectively infinite this means APs cannot be summated
relative refractory period: for several ms the threshold is higher than normal, during this time a new AP can be generated if stimulus is sufficiently strong
theoretical max frequency = 1000Hz since absolute RP = 1ms
what is Iion?
I ion is the current generated by the net movement of an ion
Iion= Gion (Vm - Eion)
^ohms law since Gion is conductance and Vm- Eion is driving force
I=gV
what happens to voltage gated ion channels as voltage increases
probability of Na + flow increases.
how do Na channels inactivate
they open with little delay, stay open for roughly 1ms then inactivate, cannot open again till they close which is most likely to happen at negative membrane potentials, molecular model for inactivation is hinge and lid model (m gate and h gate) h gate is on outside of channel m gate is inside
how do functional properties of Na channels affect AP?
inactivation of Na channels account for absolute RP
short opening time explains why APs are so brief
quick opening time explains why depolarisation occcurs so quickly
how does TTX work
inhibits Na channels by clogging up pore
