Nerves and Drugs

Question 1

What is the name given to the period when no further action potential can be produced? (1)

Answer 1

Refractory Period

Question 2

Dopamine being released in synapses leads to feelings of pleasure. Dopamine is removed from synapses by dopamine transporter proteins. Cocaine binds to this. Suggest how cocaine leads to feelings of pleasure (3)

Answer 2

• Cocaine binds to the transporter protein which prevents dopamine from binding.
• Transporter cannot move the dopamine into the cell
• Dopamine builds up in the synapse

Question 3

IFP combines with the active site of acetylcholinesterase. Explain why the muscles stay contracted (2)

Answer 3

• Acetylcholinesterase cannot break down acetylcholine

- Acetylcholine will keep generating action potentials in the membrane

Question 4

The molecular structure of cobra toxin is simliar to the molecular structure of acetylcholine. Explain why the toxin permanently prevents muscle contraction (2)

Answer 4

• The toxin binds to the receptors on the postsynaptic neurone and blocks the acetylcholine
• The acetylcholine cannot depolarise the membrane

Question 5

Explain why different proteins are required for the diffusion of different ions through the membrane (2)

Answer 5

• Each protein has a specific tertiary structure

- because ions have different shapes

Question 6

Describe how the release of acetylcholine into the neuromuscular junction causes the cell membrane of a muscle fibre to depolarise (3)

Answer 6

• movement by diffusion
• binds to receptors on post-synaptic membrane
• causing sodium channels to open

Question 7

Explain how a resting potential is maintained in a neurone (4)

Answer 7

• Na+ pumped out
• by Na-K pump
• Na+ channels are closed so can’t go back in
• inside is negative compared to the outside

Question 8

When a neurone transmits a series of impulses, its rate of oxygen consumption increases. Explain why (3)

Answer 8

• More respiration takes place
• More ATP is produced
• For active transport of Na+ out of the neurone using Na-K pump

Question 9

Sodium and Potassium ions can only cross the axon through proteins. Explain why (2)

Answer 9

• Can’t pass through phospholipid bilayer

- They’re both charged

Question 10

Describe how the resting potential is established in an axon by the movement of ions across the membrane (2)

Answer 10

• Na+ actively transported out of the axon

- K+ diffuses out of the axon

Question 11

A myelinated axon conducts impulses faster than a non-myelinated axon. Explain this difference (3)

Answer 11

• In a myelinated axon, depolarisation can only take place at the nodes of ranvier.
• The impulse jumps from node to node
• This is faster than having to depolarise the whole length of the axon

Question 12

The doctors used a statistical test to compare the results of AD and LD. P value = 0.047
What does this result show about the difference between the means for AD and LD? (2)

Answer 12

The probability of obtaining this difference by chance is less than 5% so the difference is significant.