The speed of a neural impulse
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The speed of a neural impulse
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[post_date] => 2025-01-09 08:16:01
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[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.
The sciatic nerve is the longest and widest nerve in the human body. The sciatic nerve goes from the lower back through the leg all the way down to the ankle and foot.
A study is done of different peoples sciatic nerves. In the study, the length of the sciatic nerve was measured, as well as the speed at which touch sensations were transmitted along the sciatic nerve. These measurements were taken through the use of a Nerve Conduction Velocity (NCV) test. The NCV process begins with electrically stimulating the designated nerve with a surface patch node. A separate node is placed further along down the vein in the direction of the neural flow. The second node records the new electric stimulus’ time and intensity. The distance between the two nodes and the time taken for the stimulus to reach the second node from the first node are used to calculate the velocity with which the electric pulse travels. This final number is referred to as the Nerve Conduction Velocity.
The results of the study are shown in the table below.
Table 1. Results of the NCV study.
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[question] => How long after being touched on his or her foot would it take for the nerve impulse to travel the entire length of the sciatic nerve of person C?
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[answer] => 3
[description] => Reason for the Correct Answer:
The formula for speed is speed = distance/time.
Solve for the time required for a touch impulse to travel along the sciatic nerve.
Time=distance/speed = 1.0m/(50m/s) = 0.02 seconds.
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[answers] => Array
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[each_answer] => A. 0.05 sec
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[each_answer] => B. 0.01 sec
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[each_answer] => C. 0.02 sec
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[each_answer] => D. 0.2 sec
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Assuming all else is equal, which person would take the longest to feel someone tickling his or her foot?
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
The formula to consider is speed = distance/time.
Solve for the time required for a touch impulse to travel along the sciatic nerve.
Time=distance/speed = 0.8m/(20m/s) = 0.04 seconds for person D, which is the longest time for all people.
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[each_answer] => A. Person A
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[each_answer] => B. Person B
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[each_answer] => C. Person C
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[question] => Person B and person D are both touched on the top of their feet at the same time. How much longer does it take the nerve pulse to travel the entire length of the sciatic nerve for person D as compared to person B?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
The formula for speed is speed = distance/time.
Solve for the time required for a touch impulse to travel along the sciatic nerve.
The time required for person B is 0.02 sec. The time required for person D is 0.04 sec. So the difference is 0.02 seconds.
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[answers] => Array
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[each_answer] => A. 0.02 sec
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[each_answer] => B. 0.04 sec
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[each_answer] => C. 0.03 sec
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[quiz_unique_key] => 2261298308
[question] => How long would it take the nerve impulse of person A to travel the length of a football field (90m)?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
The formula for speed is speed = distance/time.
Solve for the time required for a touch impulse to travel along the sciatic nerve.
Time=distance/speed =90m/(30m/s) = 3.0 sec.
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[answers] => Array
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[0] => Array
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[each_answer] => A. 3.0 sec
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[each_answer] => B. 1.5 sec
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[each_answer] => C. 0.67 sec
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[each_answer] => D. 0.33 sec
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[question] => A person E is tested and it is found that person E has a sciatic NCV of 120m/s, and the impulse for this person can travel along their entire sciatic nerve in a time of 0.005 seconds. How long is the sciatic nerve of person E?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
The formula for speed is speed = distance/time.
Solve for the distance required for a touch impulse to travel along the sciatic nerve.
Distance=(speed)(time)= (120m/s)(0.005sec) = 0.6 m
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[each_answer] => A. 0.60 m
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[each_answer] => B. 0.5 m
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[each_answer] => C. 0.000042 m
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[each_answer] => D. 6.0 m
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