action potential Flashcards
what is a resting membrane potential?
the potential difference that exists across the membrane of all cells
how is the membrane polarised?
there are equal numbers of + and - charges but not evenly distrubuted
how does the RMP arise?
the separation of charges on either side of the membrane
how is RMP determined?
K+ diffusion thru K+ channels, Na/K-ATPase
how can membrane potential be altered?
by applying an electric current to the cell- stimulus
what does a hyperpolarising current do?
moves MP further from 0
what does a depolarising current do?
moves MP closer to 0
what happens after a polarising current?
MP returns to original, resting level
what is an action potential?
a large change in MP- is MP raised to around -55mV large depolarisation occurs- polarisation reversed, AP amplitude independent of stimulus intensity
what happens at AP threshold?
volatage-gates Na+ channels open, Na+ diffuse in causing depolarisation
what happens at AP peak?
Na+ channels close, voltage-gated K+ channels open, K+ diffuse out causing repolarisation
what is a refractory period?
the period of inexcitability, another AP cannot be generated until the 1st has ended
what is AP propagation?
the AP in one section of axon depolarises adjacent resting parts of axon- travel along axon as waves of depolarisation
what is the function of myelination?
wrapping a layer of myelin round an axon greatly increases the AP conduction speed
what are nodes of ranvier?
myelin sheath is interrupted at intervals, here the axon membrane is exposed to ECF, ion flow can occur
