3.6.2.2 Synaptic transmission

Question 1

1) Ziconotide is a drug that can reduce severe, constant pain. Ziconotide blocks the calcium ion channels at some of the synapses which use glutamate.
Explain how ziconotide reduces severe, constant pain. (5)

Answer 1

1. fewer calcium ions enter synaptic knob
2. fewer synaptic vesicles move to/fuse with presynaptic membrane and less glutamate is released;
3. less glutamate diffuses across (synaptic cleft);
4. less (glutamate attaches) to receptors on the postsynaptic membrane;
5. fewer sodium ions enter (postsynaptic neurone) so fewer impulses (sent to brain);

Question 2

1) Suggest two reasons why the patients had ziconotide injected into their cerebrospinal fluid rather than taking a pill containing the drug. (2)

Answer 2

1.Rapidly/quickly/directly reaches spinal cord;
2. Is broken down by enzymes
OR
Is broken down by acid
OR
Is too large to be absorbed;

Question 3

1) When the patients recorded the intensity of pain, suggest two reasons why it was important to use a statistically valid scale. (2)

Answer 3

1. (Sensation of) pain is subjective
   OR
   Pain sensitivity/threshold/tolerance varies;
2. To ensure that differences (in pain detection) were (statistically) significant
   OR
   For (valid) comparison;

Question 4

2) Describe the sequence of events involved in transmission across a cholinergic synapse.

Do not include details on the breakdown of acetylcholine in your answer. (5)

Answer 4

1. Depolarisation of presynaptic membrane;
2. Calcium channels open and calcium ions enter (synaptic knob);
3. (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter;
4. Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
5. (Acetylcholine attaches) to receptors on the postsynaptic membrane;
6. Sodium ions enter (postsynaptic neurone) leading to depolarisation;

Question 5

3) Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5)

Answer 5

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).

Question 6

3) ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. (2)

Answer 6

1. Releases relatively small amount of energy / little energy lost as heat;
2. Releases energy instantaneously;
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cells.

Question 7

4) Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine.

Dopamine stimulates the production of nerve impulses in postsynaptic neurones.

Describe how.

Do not include in your answer the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones.
(3)

Answer 7

1. (Dopamine) diffuses across (synapse);
2. Attaches to receptors on postsynaptic membrane;
3. Stimulates entry of sodium ions and depolarisation/action potential;

Question 8

4) Dopamine has a role in numerous processes in the brain including pain relief. The release of dopamine can be stimulated by chemicals called endorphins produced in the brain. Endorphins attach to opioid receptors on presynaptic neurones that release dopamine.

Morphine is a drug that has a similar structure to endorphins and can provide pain relief.

Explain how. (2)

Answer 8

1. Morphine attaches to opioid receptors;
2. (More) dopamine released (to provide pain relief);

Question 9

4] GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA causes negatively charged chloride ions to enter postsynaptic neurones.

Explain how this inhibits postsynaptic neurones. [3]

Answer 9

1. (Inside of postsynaptic) neurone becomes more negative/hyperpolarisation/inhibitory postsynaptic potential;
2. More sodium ions required (to reach threshold)
   OR
   Not enough sodium ions enter (to reach threshold);
3. For depolarisation/action potential;

Question 10

5] When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.

Describe how. [3]

Answer 10

1. (Nerve impulse / depolarisation of membrane) causes Ca 2+ channel (proteins) to open;
2. Ca 2+ enter by (facilitated) diffusion;
3. Causes (synaptic) vesicles to fuse with (presynaptic) membrane;

Question 11

5] Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane.

Do not include the roles of calcium ions and tropomyosin in your answer. [2]

Answer 11

1. Myosin head attaches to actin and bends / performs powerstroke;
2. (This) pulls mitochondria past / along the actin;
3. Other / next myosin head attaches to actin (and bends / performs powerstroke);

Question 12

5] This movement of mitochondria happens when nerve impulses arrive at the synapse.

Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse. [2]

Answer 12

1. (Mitochondria) supply (additional) ATP / energy;
2. To move vesicles / for active transport of ions / for myosin to move past actin
   OR
   Re-synthesis / reabsorption of neurotransmitter / named neurotransmitter;

Question 13

6] The nerve pathway shown in the diagram may be regarded as a simple reflex arc.

Use the diagram to explain why. [1]

Answer 13

Only 3 neurones / nerve cells (in reflex arc)

Question 14

6] Suggest two advantages of simple reflexes. [2]

Answer 14

1. Rapid;
2. Protect against damage to body tissues;
3. Do not have to be learnt;
4. Help escape from predators;
5. Enable homeostatic control.

Question 15

6] In the nerve pathway in the diagram, synapses ensure that nerve impulses only travel towards the muscle fibre. [2]

Answer 15

1. Neurotransmitter only made in / stored in / released from pre-synaptic neurone;
2. (Neuro)receptors only on the post-synaptic membrane;

Question 16

6] Axon P was found to conduct impulses much faster than other axons in the nerve pathway shown in the diagram.

Describe and explain one feature of axon P that might cause this difference. [2]

Answer 16

1. Axon P is myelinated;
2. So shows saltatory conduction / impulses jump between nodes of Ranvier

OR

3. Axon P has a larger diameter;
4. So less resistance to flow of ions.

Question 17

7] The blink reflex is caused by stimulation of receptors in the eye or eyelid.

Suggest two types of stimuli to which these receptors might respond. [1]

Answer 17

Any two from:
* light
* pressure
* touch
* temperature
* chemicals
* (loud) noise
* smell;

Question 18

7] In humans, resting blink rate varies widely from 8 to 24 blinks per minute.

This variation could result in the investigations into effect of stimulation on blink rate producing means that are not significantly different. Explain why. [2]

Answer 18

1. Standard deviations / standard errors;
2. (So) likely to overlap;

Question 19

7] Some diseases cause changes in blink rate. Doctors do not often use blink rate to diagnose these diseases. Suggest two reasons why. [2]

Answer 19

1. Would not know the patient’s / human’s normal blink rate so unable to make a comparison;
2. Blink rate could be affected by stress of seeing a doctor;
3. Many factors could affect blink rate so it would be difficult to tell if blink rate was due to illness

Question 20

7] The student did not draw a line of best fit.
Suggest two reasons why. [2]

Answer 20

1. Not possible to predict intermediate values;
2. Only one result for each time period / not mean values;

Question 21

7] The student did not carry out repeats. He was still able to carry out a statistical test.
Explain why. [1]

Answer 21

Collected paired data;

Question 22

7] The blink reflex can be stopped by drugs which prevent the opening of sodium ion channel proteins in the axons of motor neurones.

Suggest how these drugs affect the passage of nerve impulses along the axons. [2]

Answer 22

1. No / low influx of sodium ions;
2. So no depolarisation / action potential;

Question 23

7] The blink reflex involves synapses. Channel proteins on presynaptic neurones are involved in reflex responses.
Explain how. [3]

Answer 23

1. Allows calcium ions in;
2. At end of presynaptic neurone;
3. Causing release of neurotransmitter;

Question 24

7] A student wanted to investigate the resting blink rate in people 60 years of age and people 15 years of age.

Describe how the student could find out whether there was a significant difference in blink rates between the two age groups. [3]

Answer 24

1. Reference to large group size;
2. Reference to matching a specific, named variable;
3. Applying a statistical test to the data;

Question 25

8] Synaptophysin is a protein involved in the production of synaptic vesicles.

Scientists can use the presence or absence of synaptophysin to identify presynaptic and postsynaptic membranes in synapses.

Explain why they are able to use synaptophysin for this purpose. [1]

Answer 25

(Synaptic) vesicles (only) found in presynaptic (part of synapse);

Question 26

8] Dopamine is a neurotransmitter. Production of too much dopamine is associated with schizophrenia. A drug used to treat schizophrenia binds to dopamine receptors in synapses. This binding does not lead to the formation of an action potential.
(i) Suggest why the drug used to treat schizophrenia is able to bind to the same receptor as dopamine. [1]

Answer 26

Has similar shape/structure to dopamine
OR
Complementary (to binding site on receptor);

Question 27

8] (ii) Suggest why binding of the drug does not lead to production of an action potential. [2]

Answer 27

1. (Binding) does not lead to opening of sodium ion channels;
2. (So) no depolarisation / threshold not reached / sodium ions do not diffuse in;

OR

3. Opens chloride ion channels;
4. Causing hyperpolarisation / preventing depolarisation