Action Potentials Flashcards
resting membrane potential
potential difference which exists across membrane of all cells
RMP facts
range 20-90mV
ICF negative
equal numbers of +ve and -ve in ECF and ICF
which ion goes in / which leaves cell
Na+ goes in K+ leaves
difference in permeability in ions for cell
Na+ resting membrane is impermeable
K+ resting membran is very permeable
diffusion gradient, what occurs
force of Na+ in, K+ out
diffusion of K+ leaves excess of -ve charge inside cell
potential gradient arising from diffusion is the resting mebrane potential
how does the resting membrane potential arise
due to the seperation of charges on either side of the membrane
diffusion of K+ from cell interior through K+ channels
small amount of Na+ leaks into cell is expelled by Na+/K+ pump
Na+/K+ pump role in ions charge
exchanges unequal numbers of Na+ and K+
moves 3Na+ outwards, 2K+ inwards [+1 outwards charge]
Na+/K+ is electrogenic
action potential threshold
-55mV
rising and falling phase of AP
rising - Na+ influx
falling - K+ efflux
-55mV, reversible RMP, overshoot from 0, influx of sodium then efflux of potassium
gate opening channels
ligand, voltage
ion selective channels
Na+, K+, Ca2+
AP is a ….. or ……
all or nothing event, amplittude is independent of stimulus
at threshold of AP
voltage gated Na+ channels open, Na+ diffuse in -> further depolarisation
positve feedback
at peak of AP
Na+ channels close, voltage gated K+ channels open, K+ diffuses out -> repolarisation
return to RMP
refractory period definition
neurons cannot generate another AP until first one is done
period of excitability
why does the refractory period occur
due to inactivation of Na+ voltage channels, inactivation gates are shut so Na+ cannot diffuse into neuron
consequences of refractory period
limits maximum firing frequency of AP in neurons
ensures unidirectional propagation of AP
prevents summation of AP
prevents summation of contractions in cardiac muscle = cardiac AP lasts as long as ventricular contraction
how does an AP crawl along axon
in one direction
from ECF to ICF in +ve to -ve directions
how does axon diameter affect speed
speed increases with axon diameter
large axons conduct impulses quicker than small
rapid conduction with very large ones
myelin increases speed of AP
does myelin increase or decrease speed of axons
myelinisation creates fast axons, without having to increase diameter that much
myelinated axon
increased AP propagation
cell membranes wrapped around axon
laid down by glial cells, insulating layer, reducing leakage
interupted at interval = Nodes of Ranvier
nodes of ranvier
myelin sheath interrupted at intervals
here the axon membrane exposed to ECF and ion flow can occur
A beta funtion
mechanoreceptors
a delta function
mechano, thermo, noci, chemo
c fibres function
unmyelinated, mechano, themro, noci
