nerve impulse Flashcards
what is a nerve impulse
self propagating wave of electrical activity which travel along an axon membrane as a response of a stimulus
what are the characteristics of the membrane in resting potential
the outside is relatively positive compared to the inside of the membrane at around -70 mv
how is this negativity achieved
they are maintained by the sodium potassium pump
why cant they travel throgh the other parts of the membrane
the phospholipid membrane is non polar so dont allow ions to pass through
how is the sodium potassium pump used
through active transport 3 sodium ions are actively transported whilst 2 potassium ions are actively pumped into the membrane
what also occurs with potasium
the pottasium ion channels open which allows pottasium ion to leave the membrane via facilitated diffusion further increasing the negativity
how are the ion channels operated
they are voltage gated and can only operate as a result of a stimulus
what is nerve stimulation
neurons are stimulated by receptor cells
what happens when there is a stimulus
it excites the neuron cell membrane which casue the na ion channel to open which causes facillitated diffusion of na ions
what is this called
depolarisation
what continue to happens
positive feedback the na ions diffuse across the axon membrane exciting more sections of the reigion which cause the ion channels to open so the membrane become less negative
what does the membrane potential reach
rises sharply until 40mv
what happens at 40mv
repolarisation
what is repolarisation the
the na ions shut and the potassium ions channel open
what does the opening of the potasium cause
the potassium ions to facillatedly diffuse out of the mebrane become more negative
what happens then
hyperpolarisation
why does hyper polarisation occur
because the potassium ions take a long time to close
what does this make the membrane and how
too negative because of the overshoot of potassium ions leaving the membrane
how is the membrane reset
using the sodium and potssium pump
when does the refractory period happen
after the action potential
what happens
as the na and ka concentration are being restored no action potentials can be fired
why can no action potential be fired
as all the na ions channels are inactive
what happens to the cell
it recovers
what does it do to the action potential
it ensures they are seperated , and are only sent in one direction
when only does action potential occur
when the membrane depolarises and reaches a threashold
what is this principle called
the all or nothing principle
what do all action potential have
the same size
so how is strength of stimulus detected
the amount of action potential at a given time a stronger stimulus will result in more action potential
what do different neurones have
different threashold values
