action potential

Question 1

At resting what is the potential across the cell membrane

Answer 1

negative resting potential

Question 2

Why is the resting potential negative

Answer 2

Neurone cell has more negative ions inside the cell than outside

Question 3

What are the positive and negative ions trying to do due to this negative resting potential

Answer 3

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

Question 4

What is the resting potential and how is it maintained

Answer 4

-70 mV maintained by keeping more positive ions outside the cell than are inside

Question 5

How are positive ions kept outside the cell

Answer 5

sodium potassium pump

Question 6

Describe the process of the sodium ion pump

Answer 6

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.

Question 7

As well as changing the ratio of negative ions in the cell to outside the cell what does the sodium potassium pump also change

Answer 7

Creates a high concentration of potassium ions inside the cell and high concentration of sodium ions outside the cell

Question 8

What is the neurone membrane permeable to

Answer 8

Potassium ions but not sodium ions

Question 9

What are the 2 gradients acting on the potassium ions

Answer 9

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)

Question 10

Which gradient has the stronger effect on potassium ions

Answer 10

Concentration gradient

Question 11

What does it mean that the concentration gradient has a stronger effect than the electrical gradient on the potassium ions

Answer 11

Even more positive ions will leave the cell creating a more negative potential

Question 12

What happens when resting potential reaches -70mV and what is this called

Answer 12

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.

Question 13

What does it mean if neurones have a negative resting potential

Answer 13

They are polarised

Question 14

Where can a neurone cell receive impulses from

Answer 14

Sensory receptors or other neurones

Question 15

What happens when an impulse is received at the dendrites

Answer 15

It triggers ACTIVATION

Question 16

What happens when ACTIVATION is triggered

Answer 16

Sodium ion channels on dendrites open

Question 17

Explain the gradients before ACTIVATION

Answer 17

• 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

Question 18

What is the resting potential called if it is in a sensory receptor

Answer 18

Generator potential

Question 19

What happens when sodium ion channels on the dendrites open

Answer 19

Sodium ions begin to enter the cell via dendrites and a positive charge begins to build up in the cell

Question 20

What is it called when the sodium ions enter the cell at ACTIVATION

Answer 20

Depolarisation as their is an increase in cell membrane potential

Question 21

What is the threshold potential

Answer 21

-50 mV

Question 22

What will happen if enough sodium ions enter the sodium ion channels at the dendrites.

Answer 22

if enough depolarisation occurs this will activate voltage-voltage gated sodium channels in the first section of the axon

Question 23

When do the voltage gated sodium channels open

Answer 23

at -50 mV

Question 24

What happens when voltage gated sodium ion channels open

Answer 24

Sodium ions rush into the axon causing even more depolarisation and even more voltage gated sodium ion channels to open (positive feedback)

Question 25

What happens when the axon achieves a positive membrane potential due to the entering of the sodium ions

Answer 25

Voltage gated potassium channels will open and voltage gated sodium channels will close

Question 26

At what membrane potential will voltage gated sodium ion channels close and voltage gated potassium ion channels open

Answer 26

+ 40 mV

Question 27

How does repolarisation occur

Answer 27

Potassium ion concentration inside the cell becomes so high that potassium ions move out of the cell.

Question 28

What may happen when repolarisation is occurring

Answer 28

So many potassium ions leave the cell the membrane potential overshoots and the membrane potential becomes more negative than resting potential causing HYPERPOLARISATION