Action potential Flashcards
what happens to the membrane and the milivolts during the action potential
-membrane is depolarised
-inside membrane changes to +40mV from -sixty mV
why is the action potential a positive feedback
during depolarisation, sodium/Na+ voltage gated channels open and Na+ rushes in causing more Na+ gates to open
what is a generator potential and what is it too small to do
-small depolarisation caused by opening of a few sodium ion channels as a result of the action of a synapse-junction between nerves-
-too small to stimulate an action potential but when more sodium voltage gated ion channels open, generator potentials are combined and the depolarisation can become large enough to pass the threshold value and cause an action potential
what is depolarisation, repolarisation, and hyperpolariation
depolarisation= temporary reversal of charge due to sodium Na+ rushing in
repolarisation= restoration of the resting potential due to potassium diffusing out as K+ voltage gated channels open
hyperpolarisation= slight overshoot of membrane potential
describe the steps of the action potential
- stimulus causes Na+ voltage gated channels to open and Na+ floods into axon
2.As Na+ ions diffuse into axon, more Na+ gate open causing greater influx by diffusion = DEPOLARISATION
3.Action potential of around +40mV established, Na+ gates close - K+ channels are open, allowing K+ to leave axon
- more K+ channels are opened so more K+ ions can diffuse out returning axon to negative value= REPOLARISATION
. overshoot due to a bit too much K+ leaving axon= HYPERPOLARISATION - K+ channels now close and activities of sodium-potassium pumps once again cause Na+ to be pumped out and K+ ions pumped in
.Axon returns to resting state
how is a local current created
- sodium ion channel open allowing sodium ions to diffuse into the neurone
- localised increase in concentration of sodium ions inside neurone= action potential
3.sodium ions diffuse long the axon/dendron way from the region of higher concentration - sodium gate, which was initially closed will open because of movement of sodium ions- allowing the action potential to move along the neurone as more sodium ions enter and set up another action potential
what is the saltatory conduction
myelination insulates electrical impulse, causing action potential to jump from one node of ranvier to another= speeding up transmission as not whole axon needs to depolarised
-elongated local current
what value is the threshold potential
about -50mV
if stimulus only causes a small amount of depolarisation there is recovery of resting potential without effect
if depolarisation reaches -50mV an action potential is created
define all or nothing principle and what does it act like
-stimulus must reach threshold value before an action potential can be triggered
-any size stimulus below this value will fail to trigger an action potential= nothing
any size above threshold will trigger an action potential= all
-acts as a filter for the brain, preventing minor stimuli from setting up impulses and potentially overloading the brain
what is the refractory period
-time when no further action potential can be generated
-straight after an action potential has been created, this is the period when Na+ voltage gated channels remain closed
-no Na+ ions can diffuse into the axon
-after an action potential the Na+ and K+ ions are in the wrong places= sodium potassium pump restores the correct concentration of sodium and potassium inside and outside
what is the purpose of a refractory period
-ensures action potential is propagated in one direction- can’t spread out in both directions
-produces discrete impulses- impulses separate from each other
-limits number of action potentials that can pass along an axon at one time
list 3 factors that affect the speeds of nerve impulse
-myelin sheath- saltatory conduction
-diameter of the axon- greater diameter= faster speed of conduction due to less leakage of ions through membrane
-temperature- higher temperatures, greater rate of diffusion, greater enzyme function in production of ATP for active transport of ions by Na+-K+ pump
how can an organism perceive the size of stimulus
-our brain can perceive stimuli of different intensities, e.g loud or quiet sounds, due to the frequency of action potentials arriving in the sensory region of the grain
-higher frequency= greater stimulus
what does a a larger stimulus means
more Na+ channels open in the sensory receptor, therefore more generator potentials and therefore more action
