ET : N - Membrane Potentials Flashcards
what are the building blocks and instruments of communication in the brain
neurons or nerve cells
which direction do synaptic potentials travel
from dendrites in towards cell body
which direction do action potentials travel
out towards axon and axon terminals
what happens to action potentials when they reach the axon terminal
info transferred to other cells through synapses
what two components does communication consist of
electrical signals (dendrites, cell body, axon) and chemical signals (synapses)
resting membrane potential of cytoplasm in comparison to extracellular space
more negative/lower than RMP of extracellular space
almost all cells in the body have a _______ RMP
negative
what two things can suddenly respond with a transient change of the potential (with an action potential) in response to a stimulus
neurons and muscle fibres
what happens to RMP when stimulus is added and what is this known as
suddenly changes and becomes positive, this is transient and goes back to negative. this is known as an action potential
what does a typical neuron consist of
soma (cell body), dendrites and a single axon
what is membrane potential
voltage across the cell membrane
what is RMP
membrane potential at rest
typical value of RMP
between -50 and -70 mV
what two techniques are used to measure intracellular potentials
the microelectrode recording technique and the patch-clamp technique
describe patch clamp technique (how does it work and what does it need)
larger tip that does not penetrate the membrane, seals to membrane (between bilipid layer and glass of clamp) creating contact between inside of cell and electronic device allowing to measure current. patch clamp needs an electrolyte otherwise current doesn’t transmit
the rmp: electrical potential difference (50 to 70 mV) across the cell membrane from _______ ___ ______. There is more ________ charges inside the cell in comparison to the extracellular fluid
separation of charge
negative
by convention, what is the potential outside the cell defined as
zero
if potential outside cell is defined as zero, intracellular potential is therefore usually _______ _____.
below zero
what three things cause rmp (very important to remember)
1) unequal concentrations of Na+ and K+ inside and outside the cell
2) unequal permeability of the cell membrane to these ions
3) electrogenic action of the Na-K pump
relative concentrations of K+ and Na+ inside and outside the cell?
concentration of potassium is much higher inside the cell than outside
concentration of sodium is much higher outside the cell than inside
how are the concentration gradients for K+ and Na+ maintained
by the Na+/K+ pump
what would happen if cells had membranes permeable to ions
the gradient would dissipate due to diffusion
the cell membrane is a little permeable to __________ and these ions will try to ____ __ the cell, the cell membrane is highly permeable to __________ and these ions will try to _______
sodium
get in
potassium
escape
what does the sodium potassium pump do that maintains conc gradients
removes the sodium that entered the cell and inserts back in the potassium that left the cell
what is the ratio of this pump
3:2 (sodium:potassium)
since it is not a 1:1 ratio, (more sodium out than potassium in) the pump removes more…
positive charges than it introduces which adds negativity to the cell in comparison to outside
what are ion channels
channels that have selective permeability to ions
what two components cause unequal permeability of the cell membrane
non-gated (leak) channels and gated channels
non-gated leak channels are ______ at rest
open
gated channels are ________ at rest
closed
in the cell membrane of neurons, there are many _______ ____ channels and very few ________ ___ channels
many leak K+ channels
very few leak Na+ channels
At rest, PK+/PNa+ =
40/1
what is the determinig factor of the resting membrane potential
the leak channels
at rest, cell membrane is much more permeable to which ion?
potassium (compared to sodium)
what does net flow of zero mean
the flow of one ion is identical to the flow of another ion in the opposite direction
what does is the equilibrium potential
an intracellular potential at which the net flow of ions is zero, in spite of a conc gradient and permeability
what can be used to calculate the equilibrium potential for each ion
the nernst equation
explain how conc gradient and electrostatic gradient is set up using potassium as an example
there is more potassium inside the cell than outside, so conc gradient is present. due to many leak channels for potassium, potassium can move from inside to outside. but when it moves outside it leaves a negative charge inside which attracts the positive potassium back into the cell - so there are two forces chemical gradient and an electrostatic force. At some point, the amount leaving will be equal to the amount entering and will create a net flow of zero
what does the equilibrium potential prevent
shifts of ions (there are shifts but net flow remains zero) and this also maintains the cons gradient
the nernst equation only applies to a situation in which …
a cell membrane is permeable to only one ion (i.e. has leak channels only for one specific ion)
glia cells have leak channels for which ion and what does this make the RMP in glia cells
potassium only and thus RMP = Ek = (-80mV)
what is the equilibrium potential for Na
~+60
what is the equlibrium potential for K
~-80
in neurons, which channels affect the RMP
both K+ and Na+
(important) The higher the permeability of the cell membrane to a particular ion… (relative to RMP)
the greater the ability of this ion to shift the RMP towards its equilibrium potential
at rest, which ion is permeability of membrane higher to (which ion is equilibrium potential closest to)
K+
in comparison to glia cells, ther RMP in neurons is… (and why)
less negative due to a small contribution of leak Na+ channels
what do you use to calulate the value of the RMP taking into account both the cons grads and the permeability of RMP to K+ and Na+ ions
the goldman equation
how many mV outside the cell
0mV
how many mV inside the cell
~-65mV
