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Question 1
The diagram below shows the structure of a synapse. |
a) | Name structures X, Y, and Z in the diagram above.
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b) | Describe the role of calcium ions in synaptic transmission.
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c) | Explain why information is only transmitted from the presynaptic neurone to the postsynaptic neurone and not in the opposite direction.
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d) | Neuromuscular junctions function in a similar way to cholinergic synapses. Describe two differences between cholinergic synapses and neuromuscular junctions.
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Question 2
Cholinergic synapses are an integral part of the human nervous system. |
a) | What is the name of the neurotransmitter used in cholinergic synapses?
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b) | Describe the roles of cholinergic synapses in the nervous system.
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c) | Describe the sequence of events in the transmission of a nervous impulse across a cholinergic synapse. You do not need to include details about the breakdown of acetylcholine in your answer.
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d) | A protein, known as synaptophysin, can be used to identify presynaptic and postsynaptic membranes in synapses. Synaptophysin is involved in the production of synaptic vesicles. Explain why synaptophysin can be used to identify presynaptic and postsynaptic membranes.
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Question 3
Dopamine is a type of neurotransmitter involved in pain relief and feelings of pleasure. The transmission of dopamine is similar to that of acetylcholine. |
a) | After dopamine has been released from a presynaptic neurone, it stimulates the production of nerve impulses in postsynaptic neurones. Explain how.
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b) | Endorphins are chemicals that stimulate the release of dopamine in the brain. They work by binding to opioid receptors on presynaptic neurones that release dopamine. Morphine is a drug that has a similar structure to endorphins. Explain how morphine can provide pain relief.
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c) | Cocaine is a drug that has a similar structure to dopamine. The diagram below shows how cocaine affects synapses in the brain.
Explain how the use of cocaine can result in feelings of pleasure.
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Question 4
The diagram below shows the structure of a synapse. |
a) | Which neurone, A or B, shows the presynaptic neurone in the diagram above?
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b) | Why does neurone A contain many mitochondria?
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c) | Dopamine is an example of a neurotransmitter. Schizophrenia has been linked to high levels of dopamine. One of the drugs used to treat schizophrenia binds to dopamine receptors within synapses. Suggest why this drug is capable of binding to dopamine receptors.
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d) | When the drug binds to dopamine receptors, no action potential is produced. Suggest why.
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Question 5
Serotonin is an example of a neurotransmitter in the brain. Serotonin diffuses across the synaptic cleft to bind to receptors on the postsynaptic membrane. |
a) | Describe how this binding causes depolarisation of the postsynaptic neurone.
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b) | Synapses are unidirectional. Explain how neurotransmitters, such as serotonin, contribute to a synapse being unidirectional.
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c) | Explain why it is important that neurotransmitters are transported back out of synapses into the presynaptic neurone.
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Question 6
Alzheimer’s disease is a non-reversible brain disorder affecting the concentration of acetylcholine in the brain. Patients with Alzheimer’s are found to have lower concentrations of acetylcholine compared to those without Alzheimer’s. This lack of neurotransmitter affects communication between nerve cells, causing memory loss and confusion. The drug donepezil can reduce symptoms of Alzheimer’s by inhibiting the enzyme acetylcholinesterase. |
a) | When a nerve impulse arrives at a cholinergic synapse, it stimulates the release of acetylcholine from vesicles in the presynaptic knob. Explain how.
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b) | Explain how a lower concentration of acetylcholine leads to fewer action potentials in postsynaptic neurones.
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c) | Suggest how donepezil could improve communication between nerve cells.
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Question 7
Gamma-aminobutyric acid (GABA) is an example of a neurotransmitter produced by neurones in the brain and spinal cord. It works by binding to postsynaptic membranes and causing the influx of negatively charged chloride ions. |
a) | Explain how the binding of GABA to postsynaptic membranes inhibits the transmission of nerve impulses.
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b) | Epilepsy occurs when there is increased activity of neurones in the brain. One form of epilepsy has been linked to abnormal GABA receptors. Suggest and explain how abnormal GABA receptors may result in epilepsy.
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c) | A different form of epilepsy occurs due to a lack of GABA. A new drug with a similar structure to GABA called vigabatrin is used to treat this form of epilepsy. Suggest how this drug might work to treat epilepsy.
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Question 8
Multiple sclerosis (MS) is a condition affecting the brain and spinal cord. It involves damage to the myelin sheaths of neurones, causing problems in controlling muscle contraction. |
a) | Describe how an action potential arriving at a neuromuscular junction results in depolarisation of muscle tissue.
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b) | MS causes muscle weakness and loss of muscle function. Suggest and describe how the function of neuromuscular junctions is affected by MS.
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c) | Some scientists investigated the use of cannabinoids to help treat muscle problems in patients with MS. Cannabinoid receptors are located in the presynaptic membrane of neuromuscular junctions. When a cannabinoid binds to a receptor, it closes calcium ion channels. Suggest how cannabinoids may prevent muscle contraction.
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