C13 - Action potential Flashcards
What is an excitable cell?
One in which the potential across the cell membrane can be altered
Neurones are excitable cells, however most other cells are not.
What is a nervous impulse?
The transmission of a change in potential…along a nerve fibre…associated with the movement of NA+ ions.
How can the change in potential accross the cell membrance be measured?
(Small change)
There is a change in voltage, which can picked up by 2 microelectrodes and fed into a Oscilloscope
The Oscilloscope monitors the way the voltage accross the cell membrane changes over time.
It is used to measure the magnitude and speed of the impulse…
and the pattern of impulses, generated in different parts of the nervous system and in different situations…
what do neurones transmit
Neurones transmit electrical impulses along the cells surface membrane surrounding the axon.
Additional point Jamie…
The change in voltage can be picked up by two microelectrodes and fed into an Oscilloscope.
This allows the magnitude and speed of the transmission of the impulse to be measured
What is action potential?
The rapid rise and fall of the electrical potential across a nerve cell membrane as a nervous impulse passes
Describe the Nobel prize conclusion on potential
The energy of the stimulus causes some of the voltage-gated sodium channels in the axon membrane to open
A voltage-gated channel is one which opens or closes in response to a particular voltage across the membrane
The sudden increase in permeability of the membrane to sodium ions allows them to rapidly diffuse into the axon, down their concentration gradient
As a result the negative charge of -70 mV inside the axon rapidly becomes a positive charge of +40mV
This is the action potential In this condition the cell membrane becomes depolarised once the potential inside the cell +40mV the sodium ion channel close preventing further influx of sodium ions
Part 2
the potassium channels open and potassium ions diffuse out, down their concentration gradient the cell becomes less positive inside as more diffuse out and the membrane is repolarised.
Part 3
More potassium ions diffuse out than Na+ ions diffused in so the potential difference across membrane becomes even more negative than the resting potential this makes the membrane hyperpolarised
Part 4
the sodium-potassium pump pumps K+ ions back in and Na+ ions back out restoring the ion balance of the resting potential
Study point
Nervous impulses are due to changes in the permeability of the axon membrane to sodium and potassium ions which change the potential difference across the membrane
Define depolarisation
a temporary reversal of potential across the membrane of a neurone such that the inside becomes less negative than the outside as an action potential is transmitted
How does the action potential travel along an axon
at the site of an action potential sodium ions diffuse into the axon
Potassium ions diffuse out
The resulting reversal of potential sets up “local currents” as sodium ions move latterally through the axon they depolarise the adjacent section of the membrane
this opens more volatage gated sodium chanels in those regions and more sodium floods in sodium ions depolarise the axon then diffuse further down the axon and in this way a self perpetuating wave of depolarisation spreaads the axon.
Part 2
the site of the intial action potential
The sodium channels are inactive and cannot open again until the resting potential has been re- established so a new action potential cant be re-established
This is known as the absolute refractory period and lasts about 1ms this is so that the action potential is not propagated back in the direction from which it came and the nervous impulse travels in only one direction
What is the absolute refractory period
period during which no new action potential may be initiated
study point
in myelinated nerve fibres the speed of transmission is up to 120 m s-1 whereras in non myelinated nerve fibres it is about 0.5 m s- 1
