nerves/ stimuli content Flashcards
resting potential
-70mV
Na+/K+ pump in cell surface membrane of axon creates conc gradient
K+ diffuse out of cell down conc grad to make outside positive and inside negative
creates potential difference
PD will pull K+ back into cell
at -70mV, two gradients counteract and there is no net movement
depolarisation
change in pd due to electrical current above threshold which makes the inside of axon positive and outside negative
depolarisation process
change in pd causes change in shape of Na+ gate- opening some voltage dependent Na/K channels
opening of more gates causes further depolarisation- positive feedback
leads to rapid opening of all Na+ gates
Na+ gates open at threshold and close at +40mV
K+ channels open at +40mV to make inside of cell more negative and close at -70mV
repolarisation
return to resting potential after a change in potential difference across the membrane
required so the membrane can conduct more impulses
repolarisation process
Na+ channels are close
permeability of membrane returns to usual, low level
K+ channels are open due to depolarisation of membrane
K+ ions move out of ion, down electrochemical gradient
inside of cell becomes more negative than the outside as K+ ions flow out
hyperpolarisation process
potassium ion channels close more slowly
K+ ions diffuse out of axon
more ions move out than at resting potential so inside of axon becomes more negative than RP- creates a PD
K+ ion channels close, K+ ions diffuse back into axon (pulled by PD)
resting potential is restored
K+ ions are completely inactive
movement of impulse
part of membrane depolarised at site of AP
depolarisation spreads to adjacent region
nearby Na+ gates respond by triggering another AP
factors affecting size of stimulus
frequency of impulses
no of neurones in a nerve that are conducting impulses
refractory period
the period in which a new action potential cannot be generated in the same section of a membrane
lasts until the voltage dependent channels return to their normal state and RP is restored
ensures that impulses only travel in one direction
myelin sheath benefits
electrical insulator across axon
increases impulse velocity in an axon
no gated voltage dependent ion channels under myelin sheath causes ions to diffuse to next node of ranvier for next gated channel
saltatory conduction
‘jumping’ of an impulse from one node to the next
faster than wave of depolarisation
synapse action
AP arrives
membrane depolarises
Ca2+ channels open, and ions enter neurone
Ca2+ ions cause synaptic vesicles containing neurotransmitter to fuse with presynaptic membrane
neurotransmitter is released into synaptic cleft
NT binds with receptors on post synaptic membrane
cation channels open
Na+ ions flow through channels
membrane depolarises and initiates action potential
when released from receptor, NT taken up across presynaptic membrane/ or diffuse away to be broken down
methods of getting rid of acetylcholine
enzymes
reabsorbed by receptors on pre synaptic membrane
diffuse away
post synaptic neurone
has specific receptor proteins with complementary-shaped binding site to part of acetylcholine molecule
acetylcholine molecule binds to receptor- changing shape of protein
- opens cation channels
- makes membrane permeable to sodium ions
- flow of Na+ ions across post synaptic membrane causes depolarisation
how memories are created
by altering the pattern of connections of neurones and strength of synapses in the brain
process of habituation
with repeated stimulation, Ca2+ channels become less responsive so less Ca2+ crosses the presynaptic membrane
less neurotransmitter is released
there is less depolarisation of the postsynaptic membrane so no action potential is triggered in the motor neurone
longer memory
involves an increase in the number of synaptic connections
repeated use of a synapse leads to creation of additional synapses between the neurones
