action potentials Flashcards
resting potential
refers to the electrical potential difference across the membrane of a neuron when the cell is not actively transmitting a signal
there are more K+ ions inside the cell and more Na+ outside the cell
sodium-potassium ATP-ase
uses ATP to pump (active transport) 3Na+ out of the cell and 2K+ into the cell
this createsa net loss of positive charge inside the cell, contibuting to the ngetaive restinng potential
what is the value for rest?
-70mV
equilibrium potential (nernst potential)
electrical potential difference (voltage) across the cell membrane at which there is no net movement of a specific ion in or out of the cell
membrane potential at which the electrical force pulling an ion into the cell exactly balances the diffusion force pushing it out of the cell
steps of electrochemical gradients and equilibrium potential
potassium ions (K⁺) will move out of the cell (through leak channels) as their concentration is higher inside the cell
as potassium ions leave the cell, they leave the inside of the cell more negatively charged relative to the outside
this negativity creates an electrical force that begins to oppose the further outward movement of potassium ions
eventually, the electrical force pulling potassium ions back into the cell becomes strong enough to counteract the diffusion force pushing them out
equilibrium potential= for that ion, the two forces—diffusion and electrical—are balanced
at this point, there is no net movement of the ion across the membrane
nernst equation
used to determine the reversal potential of a specific ion across the membrane: the membrane potential at which there is no net flux of this ion
depolarisation
depolarisation occurs in response to a stimulus
this causes a conformational change in voltage-gated Na ion channels to open
influx of Na+=reduces negative charge inside the cell causing depolarisation
if the depolarisation is string enough and reaches threshold potential, it will trigger an action potential
once threshold is reached, more voltage gated sodium ion channels open
at the peak of depolarisation, sodium channels close adn potassium channels open
what is the value for threshold potential?
-55mV
what is the value for depolarisation?
+30mV
repolarisation
activation of voltage gated potassium channels
potassium moves out- making inside less positive and membrane repolarises
hyperpolarisation
postassium channels remain open and membrane potential becomes more negative than the resting potential (relative refractory period)
this means neurons are less able to fire an action potential
value for hyperpolarisation
-80mV
what is the difference between the relative and absoulte refractory period?
absoulte= neuron cannot generate another action potential and Na+ channels are inactivated
relative= neuron can generate another action potential, but only if the stimulus is stronger than usual Na+ channels are recovering but K+ channels are still open
when does the abosulte refractory period occur?
during the depolarisation and early repolarisation phases of the action potential
how do local anaesthetics work?
lidocaine binds to Na+ channels and blocks conduction of the action potential
