Nervous Transmission

Question 1

What is potential difference?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What is the normal potential difference across a membrane?

Answer 3

Around -70mV

Question 4

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

Answer 4

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.

Question 5

What is depolarisation?

Answer 5

A change in potential difference from negative to positive.

Question 6

What is repolarisation?

Answer 6

A change in potential difference from positive back to negative.

Question 7

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

Answer 7

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

Question 8

Step 1

Answer 8

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

Question 9

Step 2

Answer 9

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

Question 10

Step 3

Answer 10

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

Question 11

Step 4

Answer 11

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

Question 12

Step 5

Answer 12

Potassium ions diffuse out of axon

Inside of axon becomes more negative than outside.

Question 13

Step 6

Answer 13

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)

Question 14

What is saltatory conduction?

Answer 14

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

Question 15

What two other factors affect speed of an impulse?

Answer 15

Axon diameter

Temperature

Question 16

How does axon diameter affect impulse speed?

Answer 16

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

Question 17

How does temperature affect impulse speed?

Answer 17

Ions diffuse faster at higher temps.

Question 18

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

Answer 18

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

Question 19

What is the all-or-nothing principal?

Answer 19

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

Question 20

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

Answer 20

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