Nervous Transmission Flashcards Preview

A Level Biology - Unit5 > Nervous Transmission > Flashcards

Flashcards in Nervous Transmission Deck (20)
Loading flashcards...
1
Q

What is potential difference?

A

The difference in charge between the inside and outside of the axon.

2
Q

What is the state of the axon membrane at resting potential?

A

The outside of the membrane is more positively charged than the inside of the axon.

3
Q

What is the normal potential difference across a membrane?

A

Around -70mV

4
Q

What 3 events happen that result in the creation of the resting potential?

A

1) 3 sodium ions are pumped out and 2 potassium ions are pumped in. This is done by a sodium potassium pump.
2) Na+ diffuse into the axon and K+ out of the axon (down an electrochemical gradient)
3) Most sodium gated channels are closed and potassium channels open so more K+ diffuse out, creating resting potential.

5
Q

What is depolarisation?

A

A change in potential difference from negative to positive.

6
Q

What is repolarisation?

A

A change in potential difference from positive back to negative.

7
Q

Describe the sequence of events that occur during an action potential across an axon.

A

The steps are labelled in the next few cards…..

8
Q

Step 1

A

Neurone has a resting potential. Some K+ ion channels are open. All Na+ voltage gated ion channels are closed.

9
Q

Step 2

A

Energy of stimulus triggers some Na+ voltage gated ion channels to open. Na+ ions diffuse into axon.
Inside of neurone is less negative

10
Q

Step 3

A

Change in charge causes more Na+ ion channels to open so more Na+ diffuse into axon.

11
Q

Step 4

A

PD reaches +40mV.
Voltage gated sodium ion channels close.
Voltage gated potassium ion channels open.
Membrane is more permeable to K+ ions.

12
Q

Step 5

A

Potassium ions diffuse out of axon

Inside of axon becomes more negative than outside.

13
Q

Step 6

A

Hyperpolarisation occurs due to lots of K+ diffusing out.
Voltage gated potassium channels close.
Axon repolarises by the sodium potassium pump (pumping 3Na+ out and 2K+ in)

14
Q

What is saltatory conduction?

A

Action potential jumps from one node of Ranvier to the next along he axon.

15
Q

What two other factors affect speed of an impulse?

A

Axon diameter

Temperature

16
Q

How does axon diameter affect impulse speed?

A

Bigger diameter means less resistance to flow of ions in the cytoplasm.

17
Q

How does temperature affect impulse speed?

A

Ions diffuse faster at higher temps.

18
Q

If temperatures go above 40 degrees, how is the impulse affected?

A

The proteins in the axon membrane denature and the ions cannot be pumped in and out, therefore the impulse can go no further.

19
Q

What is the all-or-nothing principal?

A

Only when the threshold value is reached can an action potential be created.

20
Q

How does the size of a stimulus affect the action potentials?

A

Larger stimulus means more frequent action potentials are generated.
However the size of the action potential always stays the same.