A virus which affects mouse muscles
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A virus which affects mouse muscles
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[ID] => 559180
[post_author] => 12815
[post_date] => 2025-04-28 13:56:25
[post_date_gmt] => 2025-04-28 17:56:25
[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Viruses are infectious agents that have the ability to produce a variety of structural and biochemical changes in the cells that they infect. A researcher is studying a virus that causes the selective loss of lower motor neurons in the nervous system. He is interested in seeing how changes to motor functions progress over time after infection with the virus. He believes that there will be a dose-response relationship, and that functional deficits will vary considerably depending on the amount of virus involved in the infection. To study this, he administers different amounts of the virus to different groups of mice. At a series of time points after infection, he assesses the mice with a battery of behavioral tests of neurological functions, and performs electrical tests on their nerves and muscles. At each timepoint, he also performs the tests on a group of mice that were not administered the virus. He finds that there are associations between the amounts of virus administered and speed of progression of behavioral and electrical abnormalities. The results from his study are outlined in Table 1.
Table 1
[post_title] => A virus which affects mouse muscles
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[question] => What are the target cells of lower motor neurons?
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[answer] => 3
[description] => Reason for the Correct Answer:
Autonomic neurons synapse on smooth muscle cells.
Autonomic neurons synapse on gland cells.
Lower motor neurons synapse on skeletal muscle cells.
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[0] => Array
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[each_answer] => A. Gland cells
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[each_answer] => B. Smooth muscle cells
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[each_answer] => C. Skeletal muscle cells
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[each_answer] => D. Neurons
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Which of the following best describes lower motor neurons
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
Afferent neurons bring information to the CNS.
Efferent neurons bring information from the CNS.
Afferent neurons bring information from sensory nerve fibers.
Efferent neurons bring information from the spinal cord to skeletal muscle.
Lower motor neurons are efferent neurons that originate from the spinal cord.
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[0] => Array
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[each_answer] => A. Lower motor neurons are efferent neurons that originate from sensory nerve fibers.
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[each_answer] => B. Lower motor neurons are afferent neurons that originate from sensory nerve fibers.
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[each_answer] => C. Lower motor neurons are afferent neurons that originate from the spinal cord.
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[each_answer] => D. Lower motor neurons are efferent neurons that originate from the spinal cord.
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[quiz_unique_key] => 2261298308
[question] => What abnormalities will the researcher in the passage most likely find after giving the virus to the mice?
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[answer] => 2
[description] => Reason for the Correct Answer:
If the virus causes the selective loss of lower motor neurons, spasticity should not occur; it is associated with upper motor neuron deficiencies.
If the virus causes the selective loss of lower motor neurons, somatosensation should be unaffected.
If the virus causes the selective loss of lower motor neurons, atrophy could occur.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Skeletal muscle hypertrophy
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[each_answer] => B. Skeletal muscle atrophy
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[each_answer] => C. Spasticity
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[each_answer] => D. Temperature sense loss
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[quiz_unique_key] => 2377279144
[question] => The researcher from the passage examines the results of the electrical tests on lower motor neurons. Which of the following could be a difference between the mice given the virus and the mice from the control group?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
If the virus causes the selective loss of lower motor neurons, cardiac muscle cells should be unaffected.
If the virus causes the selective loss of lower motor neurons, there could be decreased skeletal muscle tone.
If the virus causes the selective loss of lower motor neurons, fewer skeletal muscle cells may respond.
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[0] => Array
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[each_answer] => A. Fewer skeletal muscle cells responding
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[each_answer] => B. Increased skeletal muscle tone
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[each_answer] => C. Decreased response of cardiac muscle cells
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[each_answer] => D. Increased number of contracting smooth muscle cells
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[quiz_unique_key] => 83407773
[question] => What hypothesis would be best supported based on the results of the study described in the passage?
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[answer] => 4
[description] => Reason for the Correct Answer:
The results do suggest that the virus causes loss of lower motor neurons.
The study did include a control group.
The rate of lower motor neuron loss does appear to be related to the amount of virus involved in infection.
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[answers] => Array
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[0] => Array
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[each_answer] => A. The virus does not cause loss of lower motor neurons
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[each_answer] => B. The rate of lower motor neuron loss is not related to the amount of virus involved in infection
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[each_answer] => C. No conclusion can be drawn because there was no control group
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[each_answer] => D. The rate of lower motor neuron loss is related to the amount of virus involved in infection
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