15. Control and coordination
A section of Biology, 9700
Listing 10 of 130 questions
There are many mitochondria located in the presynaptic knobs of neuromuscular junctions and in the sarcomeres of muscle fibres of striated muscle. Explain the need for many mitochondria in the presynaptic knobs and in the sarcomeres. is a diagram of synapses between a postsynaptic neurone and two presynaptic neurones, X and Y. X Y postsynaptic neurone • Neurone X releases the neurotransmitter acetylcholine. • Neurone Y releases the neurotransmitter glutamate. • Both neurotransmitters bind to channel proteins in the membrane of the postsynaptic neurone. • Acetylcholine binding results in an influx of sodium ions. • Glutamate binding results in an influx of chloride ions. A student made three statements: 1. When only neurone X is stimulated, an action potential will occur in the postsynaptic neurone. 2. When only neurone Y is stimulated, an action potential will occur in the postsynaptic neurone. 3. When neurone X and neurone Y are stimulated at the same time, an action potential will not occur in the postsynaptic neurone. Explain whether or not you agree with these statements. Multiple sclerosis is a condition in which the myelin sheath breaks down in some neurones. Suggest the effect of multiple sclerosis on the transmission of action potentials in the affected neurones.
9700_w23_qp_42
THEORY
2023
Paper 4, Variant 2
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Different species of animal have neurones with different characteristics. is a diagram of a motor neurone of a rat and a motor neurone of a snail. A B C Schwann cell cell body snail motor neurone rat motor neurone axon (diameter of 40 μm) axon (diameter of 7 μm) Name the structures labelled A, B and C on . A B C The rat motor neurone has an impulse transmission speed of 50 m s–1. The snail motor neurone has an impulse transmission speed of 8 m s–1. Explain why the rat motor neurone has a faster impulse transmission speed than the snail motor neurone. shows an action potential in a rat neurone and shows an action potential in a snail neurone. −80 −40 −60 −20 membrane potential / mV rat time / ms −80 −40 −60 −20 membrane potential / mV snail time / ms Contrast the two action potentials shown in and .
9700_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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Different species of animal have neurones with different characteristics. is a diagram of a motor neurone of a rat and a motor neurone of a snail. A B C Schwann cell cell body snail motor neurone rat motor neurone axon (diameter of 40 μm) axon (diameter of 7 μm) Name the structures labelled A, B and C on . A B C The rat motor neurone has an impulse transmission speed of 50 m s–1. The snail motor neurone has an impulse transmission speed of 8 m s–1. Explain why the rat motor neurone has a faster impulse transmission speed than the snail motor neurone. shows an action potential in a rat neurone and shows an action potential in a snail neurone. −80 −40 −60 −20 membrane potential / mV rat time / ms −80 −40 −60 −20 membrane potential / mV snail time / ms Contrast the two action potentials shown in and .
9700_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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Giant axonal neuropathy (GAN) is a rare autosomal recessive disease, which affects neurones. Mitochondria can move freely within the axons of neurones. In GAN, the axons of neurones become enlarged and blocked by the accumulation of specific proteins. This prevents the free movement of mitochondria and affects the transmission of action potentials along the axon membrane. Suggest and explain why preventing the free movement of mitochondria within the cytoplasm of the axon affects the transmission of action potentials along the axon membrane. A nerve conduction velocity (NCtest can be used to measure the speed of transmission of nerve impulses along neurones in different parts of the body. NCV tests were carried out on three people with GAN. The speed of transmission of nerve impulses was measured in neurones in two nerves: • the median nerve, one of the main nerves in the arm • the peroneal nerve, one of the main nerves in the leg. Table 2.1 shows the NCV test results for the three people with GAN and the expected range for a person without GAN. Table 2.1 location of neurones speed of transmission of nerve impulse / m s–1 person 1 person 2 person 3 expected range median nerve 50–65 peroneal nerve 40–45 With reference to Table 2.1, describe the effect of GAN on the speed of transmission of nerve impulses. Walking requires nervous control to coordinate movements. One of the first signs of GAN is having problems with walking. Explain how the speed of transmission of nerve impulses in people with GAN can affect walking. GAN is caused by a mutation in a gene that codes for a protein known as gigaxonin. Scientists have tested gene therapy in mice with GAN. In one study, viral vectors containing a functioning allele of the gene that codes for gigaxonin were made. Mice with GAN were treated with one dose of these viral vectors at 12 months of age. Six months after treatment, when the mice were 18 months old, the scientists used a rotarod test to measure the effect of the gene therapy. In the rotarod test: • the length of time the mice are able to balance on a moving platform is recorded • the longer the length of time the mice can balance on the moving platform, the better their neurone activity. The rotarod test was repeated on the same mice each month until the mice were 23 months old. The rotarod test was also carried out, at the same time intervals and ages, on mice with GAN that were not treated with gene therapy and on mice without GAN. All mice were kept in the same conditions. The results are shown in . mean time balanced on moving platform / s age of mice / months mice without GAN key mice with GAN + no gene therapy mice with GAN + gene therapy
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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Questions Discovered
130