Neurones

Question 1

When the membrane is at it’s resting potential, is the inside of the membrane positively or negative charged?

Answer 1

Inside is negatively charged in comparison to the outside of the membrane as there are more positive ions on the outside of the membrane

Question 2

What does polarised mean?

Answer 2

There is a difference in charge across the membrane

Question 3

What is the voltage across the membrane when its at its resting potential?

Answer 3

-70mV

Question 4

What two mechanisms is the resting potential of the membrane controlled by?

Answer 4

Sodium-potassium pump

Potassium ion channels

Question 5

How does the sodium-potassium pump maintain the resting potential of the membrane?

Answer 5

Use active transport to move three sodium ions (Na+) out of the neurone for every two potassium ions (K+) moved in

Question 6

What is required for the active transport of K+ and Na+ ions?

Answer 6

ATP

Question 7

How do potassium ion channels (leak channels) maintain the resting membrane potential?

Answer 7

Allow facilitated diffusion of potassium ions (K+) out of the neurone, down their concentration gradient

Question 8

What is the membrane not permeable to? What does this create?

Answer 8

Sodium ions - they can’t diffuse back in

An electrochemical gradient

Question 9

What happens to the sodium ion channels (leak channels) when the neurone is stimulated?

Answer 9

They open

Question 10

What causes the membrane to become depolarised (No longer polarised)?

Answer 10

If the stimulus is big enough to cause a rapid change in potential difference

Question 11

What type of sodium ion channels are involved?

Answer 11

Voltage gated

Question 12

What is the threshold level?

Answer 12

-55mV

Question 13

What happens when a stimulus excites the neurone cell membrane?

Answer 13

Sodium ion channels open
Membrane becomes more permeable to sodium
Sodium ions diffuse into the neurone down the sodium ion electrochemical gradient created by the sodium potassium pump
- Makes the inside of the neurone less negative

Question 14

What is depolarisation?

Answer 14

If the potential difference reaches the threshold level, more sodium ion channels open causing more sodium ions to diffuse into the neurone

Question 15

What is re-polarisation?

Answer 15

• The sodium ion channels close and the potassium ion channels open
• Potassium ions diffuse out of the neurone down the potassium ion concentration gradient which starts to get it back to its resting potential

Question 16

Which ion is the membrane more permeable to?

Answer 16

Potassium

Question 17

What mV does re-polarisation occur?

Answer 17

+30mV

Question 18

What is hyper polarisation?

Answer 18

Too many potassium ions diffuse out of the neurone so there is a slight overshoot where the potential difference becomes slightly more negative than the resting potential

Question 19

Why does hyper polarisation occur?

Answer 19

The potassium ion channels are slow to close

Question 20

What is the resting potential?

Answer 20

The potential difference when the membrane isn’t being stimulated

Question 21

What is the order of events when an action potential arrives?

Answer 21

1. Stimulus
2. Depolarisation
3. Re-polarisation
4. Hyperpolarisation
5. Resting potential

Question 22

What is the refractory period?

Answer 22

Period of recovery for the ion channels and acts as a time delay between one action potential and the next

Question 23

Why is the refractory period important?

Answer 23

Makes sure that action potentials don’t overlap but pass along as separate impulses
Limits the frequency at which the nerve impulses can be transmitted and that action potentials are unidirectional

Question 24

What is a wave of depolarisation?

Answer 24

Some of the sodium ions that enter the neurone diffuse sideways
Sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part

Question 25

What is the all or nothing principle?

Answer 25

The threshold level has to be reached for an action potential to be fired

Question 26

What will a bigger stimulus cause?

Answer 26

Action potentials to be fired more frequently

It wont cause a bigger action potential as they are all the same size

Question 27

What three factors affect the speed of conduction?

Answer 27

1. Myelination
2. Axon diameter
3. Temperature

Question 28

What is myelination?

Answer 28

The neurone having a myelin sheath

Question 29

What is a myelin sheath?

Answer 29

Electrical insulator

Question 30

What is myelin sheath made out of?

Answer 30

Schwann cells

Question 31

What are nodes of Ranvier?

Answer 31

Gaps in between the Schwann cells

Question 32

What is saltatory conduction?

Answer 32

The electrical impulse jumps from node to node

Question 33

Why is saltatory conduction good?

Answer 33

It is really fast

Question 34

How does axon diameter affect the speed of conduction?

Answer 34

Action potentials conducted quicker along axons with bigger diameters because theres less resistance to the flow of ions than in the cytoplasm of a smaller axon

Question 35

How does temperature affect the speed of conduction?

Answer 35

Ions diffuse faster as the temperature increases

Question 36

What temperature does the speed of conduction start to slow instead of increase and why?

Answer 36

Around 40 degrees C

The proteins begin to denature