3.6.2.2 - SYNAPTIC TRANSMISSION

Question 1

it is important that a neurotransmitter such as serotonin is transported back out of synapse.

explain why (2)

Answer 1

1. if not removed, it will keep binding to receptors
2. keeps causing action potentials/depolaisation in post-synaptic membrane

Question 2

cannabinoids receptors are found in the pre-synaptic membrane of the neuromuscular junctions.

when a cannabinoids binds to its receptor, it closes calcium ion channels.

suggest how cannabinoids could prevent muscle contraction (4)

Answer 2

1. prevents influx of calcium ions into pre-synaptic membrane
2. synaptic vesicles don’t fuse with membrane / vesicles do not release neurotransmitter
3. neurotransmitter does not diffuse across synaptic cleft / does not bind to receptors on post-synaptic membrane
4. no action potential / depolarisation of post-synaptic membrane / sodium ion channels do not open

Question 3

cannabinoids include substances found in cannabis that can enter brain tissue.

scientists are developing artificial cannabinoids that can enter neurotransmitter junctions but cannot enter brain tissue.

suggest why these artificial cannabinoids would be better to use than cannabis when treating someone with multiple sclerosis (2)

Answer 3

1. they won’t affect synapses in the brain
2. they won’t cause problems with the brain’s function / won’t damage the brain
3. so only the neurotransmitter junctions will be affected

Question 4

when a nerve impulse arrives at a synapse. it causes the release of a neurotransmitter from vesicles in the presynaptic knob.

describe how (3)

Answer 4

1. nerve impulse/depolarisation of membrane causes calcium ion channels to open
2. calcium ions enter by facilitated diffusion
3. caused synaptic vesicles to fuse with presynaptic membrane

Question 5

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 post synaptic neurones.

describe how (3)

Answer 5

1. dopamine diffuses across synapse
2. attaches to receptors on postsynaptic membrane
3. stimulates entry of sodium ions and depolarisation/action potential

Question 6

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 6

1. inside of postsynaptic neurones becomes more negative
2. more sodium ions required to reach the threshold OR not enough sodium ions to reach the threshold
3. for action potential/depolarisation

Question 7

describe the sequence of events involved in transmission across a cholinergic synapse. (5)

do not include details on the breakdown of acetylcholine

Answer 7

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

Question 8

describe the role of calcium ions and ATP in the contraction of a myofibril (5)

Answer 8

1. calcium ions diffuse into myofibrils from sarcoplasmic reticulum
2. calcium ions cause movement of tropomyosin on actin
3. which causes exposure of binding sites on the actin
4. myosin heads attach to binding sites on actin
5. hydrolysis of ATP con myosin heads causes the heads to bend
6. bending/pulling actin molecules
7. attachment of a new ATP molecule to ech myosin head causes myosin heads to detach from actin sites

Question 9

give two reasons why transmission across a cholinergic synapse is unidirectional (2)

Answer 9

1. only presynaptic membrane releases/has acetylcholine/neurotransmitte
2. only the postsynaptic membrane has receptors

Question 10

MG is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. this can weaken contraction of muscles.

suggest and explain how MG can weaken contraction of muscles (2)

don’t include myofibril or muscle contraction in answer

Answer 10

1. less acetylcholine binds to receptors
2. less/no depolarisation/action potentials

Question 11

MG is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. this can weaken contraction of muscles.

mestinon is a drug that inhibits the enzyme acetylcholinesterase.

mestinon can help in the treatment of MG. explain how. (3)

Answer 11

1. less acetylcholine broken down
2. so more acetylcholine attaches to receptors
3. depolarisation of sarcolemma occurs OR action potential produced

Question 12

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 12

1. morphine attaches to opioid receptors
2. more dopamine released to provide pain relief

Question 13

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 13

1. morphine attaches to opioid receptors
2. more dopamine released to provide pain relief

Question 14

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 14

1. inside of postsynaptic neurone becomes more negative/hyper-polarisation
2. so more sodium ions required to reach the threshold
3. for depolarisation/action potential

Question 15

acetylcholine is a neurotransmitter which binds to postsynaptic membranes and stimulates the production of nerve impulses. GABA is another neurotransmitter. it is produced by certain neurones in the brain and spinal cord. GABA binds to postsynaptic membranes and inhibits the production of nerve impulses.

describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane (4)

Answer 15

1. AP arrives/depolarisation occurs
2. calcium ions enter synaptic knob
3. vesicles fuse with membrane
4. acetylcholine diffuses across synaptic cleft
5. binds to receptors

Question 16

acetylcholine is a neurotransmitter which binds to postsynaptic membranes and stimulates the production of nerve impulses. GABA is another neurotransmitter. it is produced by certain neurones in the brain and spinal cord. GABA binds to postsynaptic membranes and inhibits the production of nerve impulses.

the binding of GABA to receptors on the postsynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones.

explain how this will inhibit transmission of nerve impulses by postsynaptic neurones (3)

Answer 16

1. inside becomes more negatively charged/hyperpolarised
2. so stimulation does not reach threshold level/AP not produced
3. depolarisation does not occur/reduces effect of sodium ions entering

Question 17

epilepsy may result when there is increased neuronal activity in the brain.

one form of epilepsy is due to insufficient GABA. GABA is broken down on the postsynaptic membrane by the enzyme GABA transaminase. vigabatrin is a new drug being used to treat this epilepsy. the drug has a similar molecular structure to GABA.

suggest how vigabatrin may be effective in treating this epilepsy (2)

Answer 17

1. inhibits enzyme which breaks down GABA, so there is more GABA available

OR

2. binds to GABA receptors, so chloride ions enter neurone

Question 18

suggest and explain how an abnormality in GABA receptors may result in epilepsy (3)

Answer 18

1. receptors will have different tertiary/3D structure
2. shape not complementary
3. GABA cannot bind so chloride ions do not enger

Question 19

give two differences between a cholinergic synapse and a neuromuscular junction (2)

Answer 19

1. neurone to neurone VS neurone to muscle
2. AP in neurone VS no AP in muscle
3. no summation in muscle
4. muscular response is always excitatory

Question 20

describe the sequence of events which allows information to pass from one neurone to the next across a cholinergic synapse (6)

Answer 20

1. impulse causes calcium ions to enter axon
2. vesicles fuse with presynaptic membrane
3. acetylcholine released
4. acetylcholine diffuses across synaptic cleft
5. binds to specific receptors on postsynaptic membranes
6. sodium ions enter postsynaptic
7. depolarisation of postsynaptic
8. if above threshold, AP produced