action potential Flashcards
At resting what is the potential across the cell membrane
negative resting potential
Why is the resting potential negative
Neurone cell has more negative ions inside the cell than outside
What are the positive and negative ions trying to do due to this negative resting potential
Negative ions inside the cell are trying to leave as negative ions repel each other and are also attracted to positive ions as opposites attract.
Positive ions outside the cell are trying to enter the neurone cell as they repel other positive ions and attract to negative ions
What is the resting potential and how is it maintained
-70 mV maintained by keeping more positive ions outside the cell than are inside
How are positive ions kept outside the cell
sodium potassium pump
Describe the process of the sodium ion pump
Sodium potassium pump uses ATP to pump 3 sodium ions out of the cell and take 2 potassium ions into the cell. ATP is hydrolysed to ADP + Pi to provide the energy for this process. So every time this occurs there is a net removal of one positive ion from the cell.
As well as changing the ratio of negative ions in the cell to outside the cell what does the sodium potassium pump also change
Creates a high concentration of potassium ions inside the cell and high concentration of sodium ions outside the cell
What is the neurone membrane permeable to
Potassium ions but not sodium ions
What are the 2 gradients acting on the potassium ions
Electrical gradient (pulling potassium ions into the cell due to negative potential) and concentration gradient (pulling potassium ions out of the cell due to low concentration of potassium ions outside the cell)
Which gradient has the stronger effect on potassium ions
Concentration gradient
What does it mean that the concentration gradient has a stronger effect than the electrical gradient on the potassium ions
Even more positive ions will leave the cell creating a more negative potential
What happens when resting potential reaches -70mV and what is this called
The pull of the electrical and concentration gradient equal out. So the same number of potassium ions are leaving the cell as those that are entering. This is called electrochemical equilibrium.
What does it mean if neurones have a negative resting potential
They are polarised
Where can a neurone cell receive impulses from
Sensory receptors or other neurones
What happens when an impulse is received at the dendrites
It triggers ACTIVATION
What happens when ACTIVATION is triggered
Sodium ion channels on dendrites open
Explain the gradients before ACTIVATION
- Low sodium ion concentration inside neurone, high concentration outside
- Low potassium ion concentration inside neurone, high concentration outside
- High negative charge inside neurone, high positive charge outside the cell
What is the resting potential called if it is in a sensory receptor
Generator potential
What happens when sodium ion channels on the dendrites open
Sodium ions begin to enter the cell via dendrites and a positive charge begins to build up in the cell
What is it called when the sodium ions enter the cell at ACTIVATION
Depolarisation as their is an increase in cell membrane potential
What is the threshold potential
-50 mV
What will happen if enough sodium ions enter the sodium ion channels at the dendrites.
if enough depolarisation occurs this will activate voltage-voltage gated sodium channels in the first section of the axon
When do the voltage gated sodium channels open
at -50 mV
What happens when voltage gated sodium ion channels open
Sodium ions rush into the axon causing even more depolarisation and even more voltage gated sodium ion channels to open (positive feedback)
What happens when the axon achieves a positive membrane potential due to the entering of the sodium ions
Voltage gated potassium channels will open and voltage gated sodium channels will close
At what membrane potential will voltage gated sodium ion channels close and voltage gated potassium ion channels open
+ 40 mV
How does repolarisation occur
Potassium ion concentration inside the cell becomes so high that potassium ions move out of the cell.
What may happen when repolarisation is occurring
So many potassium ions leave the cell the membrane potential overshoots and the membrane potential becomes more negative than resting potential causing HYPERPOLARISATION
