action potentials Flashcards
what is paracrine signalling?
cell to cell communication where a cell produces a signal to induce changes in nearby cells
local
what is endocrine signalling?
when cells release hormones to act on distant targets
is sodium higher intracellularly or extracellulary?
extracellularly
is potassium higher intracellularly or extracellularly?
intracellularly
what three mechanisms contribute to the resting membrane potential?
passive ionic diffusion
active transport
gibbs donnan equilibrium
how does passive ionic diffusion contribute to the resting membrane?
leaky ion channels which are always open
how does active transport contribute to the resting membrane?
works against the conc gradient using the Na+/K+ ATPase
what ions does the Na+/K+ ATPase pump move across the membrane?
pumps 3 Na+ out
2 K+ in
what is the voltage of the ECF with respect to the ICF?
positive
what is the resting potential?
-70mV
what is the nernst equation?
relates membrane potential to the concentration gradient
Em = 61.5 x log [conc outside]/[conc inside]
what are action potentials?
rapid changes in voltages
what is the axon hillock?
the trigger region
generates the action potential
what are the two gates of the voltage gated sodium channels?
activation gate
inactivation gate
when does the sodium channel activation gate open and how fast is it?
in response to depolarisation
v fast
when does the inactivation gate of the sodium channel close?
in response to depolarisation
how do K+ channels cause hyperpolarisation?
stay open for longer
explain the stages of an action potential
resting potential - -70mV depolarisation - sodium channels open repolarisation - potassium channels open hyperpolarisation - potassium takes ages to shut refractory period
what is the absolute refractory period?
when the sodium channels cannot open regardless of the size of the stimulus
what is the relative refractory period?
when a suprathreshold stimulus can stimulate the opening of sodium channels
threshold is increased
how do local anaesthetics work?
bind to sodium channels in their active state
inactivates them
prevent it from returning to resting state and stimulating APs
