Passive properties and excitability of the membrane Flashcards
what’s the equivalent circuit model?
representing ion channels impact in terms of electrical behaviour
what’s the symbol for battery/ion pump?
https://www.google.com/search?q=battery+circuit+symbol&safe=active&rlz=1C1CHBF_en-gbGB767GB767&sxsrf=ACYBGNTXpxpx5zSUsRdRIFpPI4V57wOWlA:1579437266082&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjB7sGp1o_nAhUYThUIHfqxBokQ_AUoAXoECA8QAw&biw=1280&bih=616#imgrc=rCiZiuvofV6iFM:
what does the ion channel/ battery generate?
voltage
what is voltage also known as?
electromotive force
what does the voltage determine?
current flow
for each set of ion channels, what does EMFion equal?
Eion for each set of ion channels
what is driving force?
difference between membrane and equilibrium potential
in the membrane what does conductance represent?
ion channel permeability
what is conductance?
how readily a current will pass through a material
how are conductance and resistance related?
inversely proportional (opposites)
what is resistance?
how much a material opposes the flow of current
what are the 2 assigned units for conductance?
Siemens (S) or Ohms-1 (Ω-1)
in the membrane is conductance constant or variable?
variable
what does conductance determine in membrane?
current at a particular membrane potential
what is ohms law?
the relationship between voltage and current
what equation represents the relationship between membrane potential, equilibrium potential, voltage and conductance?
(Vm- Eion)= Iion/ Gion
(membrane potential- equilibrium potential) = voltage/ conductance
if Vm=Eion is there current?
no
draw the symbol for capacitance
https://www.google.com/search?safe=active&rlz=1C1CHBF_en-gbGB767GB767&biw=1280&bih=616&tbm=isch&sxsrf=ACYBGNTnNiCP2mSg0C0qGFQny1V7D9n2Tw%3A1579437270517&sa=1&ei=1kwkXoWKH_zTgwep_oD4Ag&q=capacitance&oq=capacitance&gs_l=img.3…459116.460592..460868…0.0..0.0.0…….0….1..gws-wiz-img.vRUdKOzR7Zc&ved=0ahUKEwiFzdCr1o_nAhX86eAKHSk_AC8Q4dUDCAc&uact=5#imgrc=EPmf5l-w2v0LUM:
what do capacitors do?
store charge
what is a capacitor?
2 conductors separating by non-conductive material
what, biologically acts as a capacitor?
membrane
what are the units of capacitance?
Farad (F)
give the equation to calculate capacitance
Capacitance (C)= Stored charge (Q)/ Voltage (V)
if there’s capacitance what happens as potential difference (voltage) increases, what happens to stored charge?
it also increases
if there’s capacitance and potential difference reduces, what happens to stored charge?
it also reduces
what occurs due to charge being moved on and off a capacitor?
capacitive current
does capacitive currents affect IC conc/ ion gradients?
no- as long as the voltage change is <100 mV (+ or -)- as only a relatively small number of ions are required for capacitance
what membrane factor determines total capacitance?
surface area of membrane
if you simplify the equivalent circuit model, what 3 components are important?
- conductance
- equilibrium potential
- capacitance
how is total conductance calculated?
sum of all conductances
how is total current calculated?
sum of all currents
how is passive and active membrane behaviour recorded?
2 electrodes- one applies current to one part, another records current in another part
if a negative current is applied, what happens to membrane?
hyperpolarisation
if a positive current is applied, what happens to membrane?
depolarisation
what’s different between current injected and current recorded?
current injected is seen as square
current recorded has lag
if current was affected by conductance only, how would the current recorded look?
also a square
what is causing the lag?
capacitance- must obey capacative law
what is tau?
time constant
what is time constant?
time taken to achieve a 63% change in voltage
how is voltage calculated by rearranging capacitance equation?
V= Q/C
how does increased capacitance affect rate of change?
reduces it
how does decreased capacitance affect rate of change?
increases it
how is Tau (t) calculated? (2 ways)
t= C x R time constant = capacitance x resistance or t= C/G time constant = capacitance/ conductance
is capacitance usually constant or variable in a cell membrane and why?
constant as cell membrane SA doesn’t change
if the duration of a stimulus is short, what must the intensity be to reach threshold?
high
if the duration of a stimulus is long does the intensity need to be long to reach threshold?
no
what are the 2 affects of conductance on membrane?
higher conductance , lower response
lower conductance, higher voltage
higher conductance, reduced Tau- reaches threshold quicker
how is conductance related to neuromodulation?
inhibitory neurotransmitters increase conductance e.g. GABA
excitatory neurotransmitters reduce conductance e.g. glutamate
is an elongated structure leaky?
yes
the further away from source of current, how does current change?
gets lower- due to leakiness
