Unit 2: The Nerve Impulse

Question 1

What do neurones do?

Answer 1

transmit impulses to other neurones to effect a response

Question 2

What does the sodium/potassium pump in the membrane of the axon do to maintain resting potential?

Answer 2

actively transports 3 sodium ions out of the membrane and 2 potassium ions into the membrane.

Question 3

What gives the sodium/potassium pump energy to transport ions in and out of the membrane

Answer 3

Dephosphorylation of ATP

Question 4

Describe the charges inside and outside of the membrane of an axon at resting potential

Answer 4

Outside of the membrane more positive than inside which is less positive (so relatively negative)

Question 5

Why are voltage gated protein channels different to normal protein channels?

Answer 5

because they open / close depending on the charge of the membrane.

Question 6

What do voltage gate channels do?

Answer 6

Change the permeability of the membrane to certain ions at different voltages.

Question 7

How do the voltage gated channels maintain resting potential?

Answer 7

The potassium voltage gated channels are open and potassium diffuse out of the membrane down the electrochemical gradient. The Na VG channels are closed.

Question 8

What charge is the inside of the neurone at resting potential?

Answer 8

-70mV

Question 9

What is depolarisation?

Answer 9

when energy from an impulse causes the temporary reversal of charges so the inside of the membrane becomes positive and the outside becomes negative.

Question 10

What happens during depolarisation?

Answer 10

The sodium voltage gated channels open so that sodium ions diffuse in down the electrochemical gradient and the K VG channels close.

Question 11

What is the charge of the neurone at action potential?

Answer 11

+40mV

Question 12

What is an action potential?

Answer 12

change in the electrical potential associated with the passage of an impulse along a membrane

Question 13

What is repolarisation?

Answer 13

when the membrane gets restored back to its original polarity

Question 14

Describe what happens during repolarisation

Answer 14

When an action potential reaches +40 mV, it causes the sodium VG channels to close and the potassium channels to open. K ions diffuse out the membrane down the electrochemical gradient

Question 15

What is hyperpolarisation?

Answer 15

when the axon reaches a more negative charge inside usual (at resting potential).

Question 16

What is charge inside of the neurone when hyperpolarisation occurs?

Answer 16

-90mV

Question 17

Why do neurones become hyperpolarised?

Answer 17

there is a delay in the closing a potassium voltage gate channels.

Question 18

How are nerve impulses started?

Answer 18

by receptor cells in living organisms

Question 19

How are nerve impulses propagated along an neurone?

Answer 19

an action potential starts in one part of the axon which causes it to become depolarised. This acts as a stimulus for the next area to become depolarised. The area behind eventually becomes repolarised and then goes back to resting potential.

Question 20

What is saltatory conduction?

Answer 20

When action potentials jump from one node of ranvier to another

Question 21

What is the advantage of saltatory conduction?

Answer 21

impulses travel a lot faster

Question 22

Why do action potentials only occur at the nodes of ranvier in a myelinated axon?

Answer 22

Because the myelin sheath acts as an electrical insulator, preventing action potentials from forming along the myelinated parts of the neurone.

Question 23

What is the refractory period?

Answer 23

the resting period of an ion channel. After an ion channel has opened, there is a rest period before it can open again.

Question 24

What prevents action potentials travelling in both directions?

Answer 24

the refractory period

Question 25

What does the refractory period do?

Answer 25

makes separate discrete impulses and limits the number of action potentials in an axon at one time.

Question 26

Why are impulses described as ‘all-or-nothing’?

Answer 26

Action potentials are only triggered when the stimulus is of a certain level. If threshold potential is not reached, there is no action potential and conversely no matter how much the threshold potential is exceeded, the strength of the stimulus will be the same.

Question 27

What is threshold potential?

Answer 27

It is a critical level to which a neurone can go from resting potential to an action potential.

Question 28

How can you measure the strength of a stimulus?

Answer 28

by the frequency of nerve impulses it causes

Question 29

Give an example of a weak stimulus and describe the frequency of nerve impulses

Answer 29

dim light or a quiet sound is a weak stimulus that would cause a low frequency of nerve impulses along a synapse.

Question 30

Give an example of a strong stimulus and describe the frequency of nerve impulses

Answer 30

A loud sound or bright light would be a strong stimulus that would cause a high frequency of nerve impulses along a sensory neurone

Question 31

Why is important that nerve impulses get from one part of the body to another quickly?

Answer 31

to allow fast response to a stimuli

Question 32

What are three factors that affect the speed of nerve impulses?

Answer 32

Temperature, axon diameter, whether or not is it myelinated

Question 33

How does temperature affect the speed of nerve impulses?

Answer 33

At higher temperature, faster transmission. Active transport that is needed for the Na/K pumps require ATP which is made in respiration which is an enzyme controlled reaction.

Question 34

Endothermic animals have slower responses: True or False? Why?

Answer 34

False, they have quicker responses because they are able to keep their body temperature constant despite the temperature and so are not effected as much in colder conditions.

Question 35

How and why does axon diameter affect the speed of nerve impulse?

Answer 35

a larger diameter means faster transmission. Less leakage of ions from a bigger axon. Leakage makes membrane potentials harder to maintain.

Question 36

What type of animals tend to have a larger axon diameter?

Answer 36

aquatic animals e.g. squid

Question 37

How does the myelin sheath affect speed of nerve impulses?

Answer 37

Myelin sheath act as electrical insulators and so the action potential only happen at the Nodes of Ranvier. Action potentials jump from one node to the next by saltatory conduction. Increases speed dramatically.