resting membrane potentials

what is the resting membrane potential (3)

• The membrane potential refers to the separation of opposite charge that exists across the cell membrane

• The difference in electric charge between the inside and outside of a neuron's cell membrane/ axon

• Inside of an axon has a more negative charge compared to the outside which has a more positive charge

what is the typical value of the resting membrane potential

-70 mv

show a diagram of how to measure the RMP in a neuron

Note when drawing the voltmeter make sure one wire is IN the membrane and one is clearly OUT - so you can actually measure the RMP make this clear !!!

what causes the RMP (3)

•       an unequal distribution of key ions

•       the selective permeability of the membrane – more permeable to K+ / less permeable to Na+

•       the Na⁺K⁺ ATPase pump = pumps 2K⁺ into the cell for every 3Na⁺ out of the cell – NOWT KIN

why is the membrane more permeable to K+ (2)

• because of the presence of leakage channels

• therefore K+ is the cation for which there is the greatest amount of leakage (though leakage channels) across the resting plasma membrane

how is the RMP established / maintained across the axon membrane in a neuron (5)

• Na+/K+ pump actively transports 3 Na+ out and 2 K+ into the axon (NOWT KIN)

• this creates an electrochemical gradient: higher concentration of K+ inside the axon and a higher concentration of Na+ outside the axon

• membrane is more permeable to K+ / less permeable to Na+

• K+ diffuses out of the axon by facilitated diffusion but Na+ cannot diffuse in

• also negatively charged proteins/intracellular proteins inside the axon - cannot leave as the membrane is not permeable to them (0 relative permeability)
  (Basically this all contributes to the -70mv and establishes how it's more positive outside the axon and more negative inside)

explain what polarized means and give an example

something that is charged

eg - RMP = -70 mv

explain what depolarized means and give an example

a reduction in charge

eg = -70 mv goes to -30 mv - less charge across the cell membrane

explain what hyperpolarized means and give an example

means an increase in charge

eg = -70mv goes to -90 mv

how is a membrane described as having no potential

membrane has no potential if: there is an equal number of positive and negative ions/charge inside and outside the membrane

how is the membrane described as having potential

• membrane has potential (unequal distribution/separation of charge) if:

• there is more positive charge outside than inside (positive charge has moved from inside to outside) =

where do the separated charges lie (4)

• the excess negative and positive charges are attracted to each other and line up on the layer / edge of membrane potential

• however remainder of inside and outside of cell = neutral

• separated charges lie on the thin layer on the membrane potential

• only takes a few small changes in order for there to be a membrane potential

which membrane has more potential

c

For an open channel, what factors determine in which direction ions move through the channel?

Both – the electrochemical gradient (concentration and membrane potential / electrical gradient)