lecture 4 Flashcards
(22 cards)
where does neural electricity come from?
the ionic currents generated by the diffusion of 4 ions
Na K Ca Cl
what is the difference between active and passive neuronal electrical signals
passive- voltage change is proportional to amount of current injected
active- above threshold, cell generates action potential
where does membrane potential come from
different concentrations of ions inside and out a selectively permeable cell surface membrane
how are changes in voltage across the membrane produced
changing the selective permeability of the membrane for different ions
why are squid channels very similar to humans although they have different concentrations of ions
because the membrane potential is related to the ratio of ions, not the number
how do ions move across neuronal membranes
active transporters- move selected ions against gradient
ion channels- allow ions to diffuse down gradient
selectively permeable
what determines an energy source from a ion
equilibrium condition:
concentration
charge
voltage difference
what is needed to “harvest” energy from the concentration gradient
permeability
electrochemical gradients
energy stored in the form of voltage or concentration differences
what part of nest is electrical work
zFV
what part of nest is chemical work
RT ln (X1/X2)
what is Nerst equation
V=(RT/zF)ln(X2/X1) -OUT OVER IN or Ex (equilibrium potential of ion x/reversal potential to change direction of ions)
what is the volts at 18 degrees
0.058V
what is the volts at 37 degrees
0.062V
what is the volts at 10 degrees
0.056V
how many ions move during a voltage change
only a small fraction are needed to create the gradient, 1/100,000 for a 100mV difference
what are the implications of no net flux
reversal potential is also the equilibrium potential
what determines the resting membrane potential
the potassium concentration gradient over membrane
why is the slope not as steep as nests equation predicts
because real neutrons are permeable to more than one ion (mostly to K)
what equation combines the estimates of all ion species
goldmae-hodgkin Katz (GHK)
when can the membrane potential of a neuronal change from resting potential to a new potential
permeability: changes one one species is not at equilibrium, can change quickly
concentration of an ionic species changes
activity of an electrogenic pump changes
how does permeability change
the opening and closing of voltage gated and ligand gated channels
