U6T5 – Nerves: Conduction Along Axons

Nerves: Conduction Along Axons

1 / 15

After an action potential has fired, the refractory period acts as the following:

a) Prevents action potentials overlapping
b) Limit the frequency of action potentials
c) Limit the size of action potentials
d) Makes action potentials travel unidirectionally.

b, c, d

a,b,c,d

a, b, d

2 / 15

In the above diagram, which graph shows the correct effects of increasing a stimulus?

A

B

Neither

3 / 15

Many peripheral neurones (including motor neurones)have cells wrapped around the axon.

What are these cells called? ( type your answer- watch your spelling).

4 / 15

Cells wrapped around peripheral neurones contain a membrane with a high content of a fatty substance forming a sheath.

What is the name of this fatty substance? ( Type your answer).

5 / 15

What the the tiny gaps called labelled X on the above diagram? ( Type your answer)

6 / 15

What is the main function of the fatty substance wrapped around peripheral nerve axons?

Thermal Insulators

Electrical Insulators

Waterproof Layer

7 / 15

When an action potential is generated, there is a temporary reversal of the polarity of the neurone membrane at that point. Does this mean that:

The inside becomes more negative compared to the outside.

The outside becomes more negative compared to the inside.

The outside becomes more positive compared to the inside.

8 / 15

Once an action potential has been generated, what causes the next section of the axon membrane to become depolarised?

Some sodium ions diffuse through the cytoplasm, and cause voltage gated sodium channels to open.

Some potassium ions diffuse through the cytoplasm, and cause voltage gated potassium channels to open.

Voltage gated sodium channels are open all the time, so the sodium ions just diffuse out.

9 / 15

Once an action potential has been generated, why is the wave of depolarisation only in one direction?

Hyperpolarisation means potassium channels are working at capacity.

Sodium ions only ever diffuse away from the cell body.

The refractory period means that voltage gated channels are 'locked' closed.

10 / 15

Why is the speed of conduction faster on myelinated neurones?

The sheath creates a hydrostatic pressure, pushing the ions and therefore the action potential along.

The sheath keeps the axon warmer, therefore diffusion is faster.

Due to action potentials only occurring at the gaps between the sheath, so the impulse 'jumps' between them.

11 / 15

Name the term given to the 'jumping' of an action potential long a myelinated neurone.( Type in your answer)

12 / 15

True or False - The speed of conduction along an unmyelinated neurone is around 5 m/s ( jogging pace).

TRUE

FALSE

13 / 15

True or False - Axons with a narrower diameter have a faster speed of conduction.

TRUE

FALSE

14 / 15

Axons with a wider diameter axon have...

More sodium ions for diffusion.

More resistance to the flow of ions through the cytoplasm.

Less resistance to the flow of ions through the cytoplasm.

15 / 15

Why does an increase in temperature ( up to 40 degrees) cause an increase in the speed of conduction along a neurone?

Faster production of ATP.

Faster rate of enzymes.

Faster rate of diffusion of ions.

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