Topic 6D+E: Nervous Coordination and Synaptic transmission

Question 1

Explain how a resting potential is maintained in a neurone. [5]

Answer 1

1. Na+ actively transported out (of neurone) and K+ in;
2. by Na+/K+ pump protein;
3. 3 Na+ (actively transported) out for every 2 K+ in;
4. (Membrane) more permeable to K+ (leaving than Na+ entering);
5. Higher concentration of K+ inside and higher concentration of Na+ outside (the neurone)

Question 2

Explain why the resting potential of a neurone increases if a respiratory inhibitor is added. [3]

Answer 2

1. No/less ATP produced;
2. No/less active transport;
3. Electrochemical gradient not maintained

Question 3

Explain why different proteins are required for the diffusion of different ions through the cell-surface membrane. [2]

Answer 3

1. Each protein has a specific tertiary structure;
2. Because the ions have different sizes/shape/charge

Question 4

Explain why the cell-surface membrane of a neurone is more permeable to potassium ions than to sodium ions. [1]

Answer 4

1. More K+ leak channel proteins

Question 5

Sodium and potassium ions can only cross the axon membrane through proteins.

Explain why. [2]

Answer 5

1. Can’t pass through phospholipid bilayer;
2. because charged

Question 6

After exercise, some ATP is used to re-establish the resting potential in axons. Explain how the resting potential is re-established. [2]

Answer 6

1. Active transport against concentration gradient;
2. Of sodium ions out

Question 7

Damage to the myelin sheath slows down the transmission of nerve impulses.

Explain why. [3]

Answer 7

1. Less/no (electrical) insulation;
2. Less/no saltatory conduction;
3. Depolarisation occurs along whole length (of axon)

Question 8

Suggest and explain why damage to the myelin sheath of neurones of the autonomic nervous system cause heart rate irregularities? [3]

Answer 8

1. Fewer impulses along sympathetic/parasympathetic (pathway/neurones);
2. (Impulses) from medulla;
3. To SAN

Question 9

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 9

1. Depolarisations of presynaptic membrane;
2. Calcium ion channels open and calcium ions enter (synaptic knob);
3. (Calcium ions cause) synaptic vesicles 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 10

Ziconotide is a drug that blocks calcium ion channels. Explain how ziconotide reduces severe, constant pain. [5]

Answer 10

1. No/fewer calcium ions enter synaptic knob;
2. No/fewer synaptic vesicles fuse with presynaptic membrane and no/less neurotransmitter is released;
3. No/less neurotransmitter diffuses across (synaptic cleft);
4. No/less (neurotransmitter attaches) to receptors on the postsynaptic membrane;
5. No/fewer sodium ions enter (postsynaptic neurone) so no/fewer impulses (sent to brain)

Question 11

Scientists investigated the effectiveness of a drug on reducing pain. The drug is a polypeptide and was injected into each patient’s cerebrospinal fluid that bathes the brain and spinal cord.

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

Answer 11

1. Rapidly reaches spinal cord;
2. Is broken down by enzymes

Question 12

Describe how acetylcholine stimulates the production of nerve impulses in postsynaptic neurones. [3]

Don’t include the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones. [3]

Answer 12

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

Question 13

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 13

1. (Inside of postsynaptic) neurone becomes more negative;
2. More sodium ions required (to reach threshold);
3. For depolarisation

Question 14

Donepezil inhibits the enzyme acetylcholinesterase. Explain how donepezil could improve communication between nerve cells. [3]

Answer 14

1. Less/no acetylcholine broken down;
2. Acetylcholine attaches to receptors;
3. (More) Na+ enter to reach threshold / for depolarisation

Question 15

A myelinated axon conducts impulses faster than a non-myelinated axon.

Explain this difference. [3]

Answer 15

1. Myelination provides (electrical) insulation;
2. (In myelinated) saltatory (conduction);
3. In non-myelinated depolarisation occurs along whole axon

Question 16

Serotonin is a neurotransmitter. It diffuses across the synaptic cleft and binds to a receptor on the post-synaptic membrane.

Describe how this causes depolarisation of the post-synaptic membrane. [2]

Answer 16

1. Causes sodium ion channels to open;
2. Sodium ions enter (cell and cause depolarisation)

Question 17

It is important that neurotransmitters are transported back out of synapses. Explain why. [2]

Answer 17

1. (If not removed) keeps binding (to receptors);
2. Keeps causing action potentials/depolarisation (in post-synaptic membrane)

Question 18

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

Explain why scientists can use the presence or absence of synaptophysin to identify presynaptic and postsynaptic membranes in synapses. [1]

Answer 18

1. (Synaptic) vesicles (only) found in presynaptic (part of synapse)

Question 19

Give two reasons why transmission across a cholinergic synapse is unidirectional. [2]

Answer 19

1. (Only) the presynaptic neurone/knob releases neurotransmitter/acetylcholine;
2. (Only) the postsynaptic neurone has receptors