6.4 Nerve impulses Flashcards
what are nerve impulses
electrical charges transmitted along a neurone
how are nerve impulses created
movement of sodium potassium ions
what charge is the outside of the membrane when the cell is resting
postive
(more positive ions outside of the cell than inside)
what is the membrane if there are more postive ions outside than inside
polarised > difference in charge across it (PD)
what is the voltage at resting potential
-70mV
how is the resting potential created and maintained
sodium potassium pumps
potassium ion channels
what are sodium potassium pumps
use active transport to move 3 NA+ out of the neurone for every 2K+ moved in
- ATP required
what are potassium ion channels
allow facilitated diffusion of K+ out of the neurone down the concentration gradient
is the membrane permeable or impermeable to sodium ions
impermeable
how is a sodium ion electrochemical gradient created
- sodium ions can’t move back into the membrane
- more postive sodium ions outside than inside
what channels are open when the cells at rest
potassium ion channels
is the membrane permeable or impermeable to potassium ions
permeable so some diffuse back out through potassium ion channels
what ion channels open when a neurone is stimulated
sodium ion channels
what happens during stimulus
- membrane becomes excited
- NA+ channels open
- membrane becomes more permeable to NA+ so they moved down the NA+ electricocjemical gradient
- inside of neurone is less negative
what happens in depolarisation
- if PD reaches threshold more NA+ channels open so more NA+ diffuses in
what happens in repolarisation
- at 30mV NA+ channels close, K+ opens
- membrane is more permeable to K+ so K+ diffuses out down K+ ion concentration gradient
- membrane gets back to resting
what mV is threshold
-55mV
what happens in hyper polarisation
- K+ ion channels close slowly so slight period of time where too many diffuse out of neurone
- PD BECOMES MORE NEGATIVE TJAN RESTING
what happens in resting potential
- sodium potassium pump returns membrane to resting potential by pumping sodium ions out and potassium ions in
what is a refractory period
- time no action potential can be made
- NA+ closed during repolarisation and K+ closed during hyper polarisation
what does the refractory period allow
action potentials to be seperate from each other
what is a wave of depolarisation
- some NA+ diffuse sideways which causes NA+in next region to open and they diffuse into there
what does propagate mean
wave like movement
what is the all or nothing principle
once threshold reached, an action potential will always fire with the same change in voltage not matter size of stimulus
what are 3 factors that affect the speed of conduction
myelination
axon diameter
temperature
what is the myelin sheath
electrical insulator
what is the myelin sheath made from in the personal nervous system
schwann cells
where are the sodium ion channels concentration
nodes of ranvier
what is saltatory conduction
in a myelinated neurone depolarisation only happens at the nodes of ranvier
- neurons cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node
how do impulses travel in a non myelinated neuron
as a wave across the whole length of the acon membrane
— depolarisation across whole membrane
—- slower than saltatory conduction
how does axon diameter affect action potentials
action potentials are conducted quicker across axons with bigger diameter as there is less resistance to the flow of ions than in cytoplasm of smaller axon
— less resistance means depolarisation can reach different parts of membrane quicker
how does temperature affect action potentials
speed of conduction increases with temperature as ions diffuse faster
— only until 40 as proteins start to denature (pumps and channels
