Action Potentials Flashcards
what is depolarisation?
when the membrane potential becomes less negative
what is hyperpolarisation?
the membrane potential becomes more negative
what causes a change in membrane potential?
ionic movements across the membrane
what two things determine the change in membrane potential?
direction of movement of the ion
charge on the ion
what direction is influx?
into the cell
what direction is efflux?
out of the cell
what drives passive movement of an ion through a channel?
its electrochemical gradient
when does movement of sodium ions occur?
in response to the opening of sodium selective channels on the cell membrane
what direction does sodium flow and why?
into a cell
its concentration and electrical gradients are inward
what is the value of the membrane potential and what represents this?
Vm = -70mV
what is the equilibrium potential for sodium?
Ena = +60mV
what is the driving force for sodium influx and when does sodium move into the cell?
Vm - Ena
when this is negative
what is Ina?
the current carried by sodium ions
Ina = gna(Vm-Ena)
what is Gna?
the sodium conductance
when does movement of potassium occur?
in response to the opening of potassium selective channels
which direction does K move in and why?
outwardly
its concentration gradient is outwards and greater than its inwards electrochemical gradient
what is the equilibrium potential for potassium?
Ek = -100mV
what is the driving force for K+ efflux?
Vm-Ek
moves outward when positive
what are ion channels?
proteins that span the lipid bilayer forming pathways for selected ions
what states do ion channels have and cycle between?
open (o) and closed (c)
name two types of gated ion channels and state what opens them
voltage gated ion channels (opened by changes in membrane voltage)
ligand gated ion channels (opened when chemicals bind)
what ion channels are responsible for the action potential in neurons?
voltage gated ion channels (VGICs)
voltage gated sodium and voltage gated potassium channels
opening of which channel causes Vm to depolarise?
voltage gated sodium channels
opening of which channel causes Vm to hyperpolarise?
voltage gated potassium channels
what is an action potential?
a brief electrical signal in which the polarity of the membrane is momentarily reversed
when is an action potential generated?
when the stimulus reaches threshold
what does opening of a few sodium channels cause and what is this an example of?
the opening of further channels
positive feedback
what does opening of a few potassium channels cause and what is this an example of?
closing of channels
negative feedback
what happens to sodium channels during maintained depolarisation?
they enter a non-conducting inactivated state
how does a sodium channel enter its closed state?
when repolarisation occurs
what is the absolute refractory period?
no stimulus can elicit a second AP
all sodium channels inactivated
what is the relative refractory period?
a very strong stimulus may be able to elicit a second AP
what substance surrounds axons?
myelin
what produces myelin in the PNS?
schwann cells
many surround a single axon
what produces myelin in the CNS?
oligodendrocytes
one surrounds many axons
what are oligodendrocytes and schwann cells?
types of macroglia
is conduction faster in a myelinated axon or non myelinated axon?
myelinated
