TITLE: Nervous Reflex Lab
OBJECTIVE: Students will be able to explain how the entire nervous system can be considered a system of
innumerable reflex arcs.
MATERIALS: mallet, cotton swab, textbook, ruler, light, cotton ball
INSTRUCTIONS for DATA collection: Complete the following activities and answer the corresponding
questions in each section. Answers should be written in complete sentence format.
Possible abnormal spinal reflex results include: hyperflexia (exaggerated response), which results from
damaged or diseased motor areas in the CNS; and hypoflexia (inhibited response), which results from
degeneration of nerve pathways, voluntary motor control, and other factors.
Patellar Reflex (aka. knee-jerk reflex)
This reflex is mediated by a two-neuron arc centered in the spinal cord.
1. Subject should sit on the edge of a table or chair so that his leg hangs freely. The observer should
locate the patella and the tendon below it. Then tendon should then be struck sharply with the flat
end of the mallet. If done properly, this should produce the patellar reflex. The tap stretches a
quadriceps muscle in the anterior thigh, stimulating stretch receptors located in the muscle. In
response to the increased stretch, this normally would only occur when the muscle load has suddenly
increased, the muscle contracts and extends the lower leg.
2. Describe your results. 3.5 points
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3. Repeat the above procedure but have the subject interlock his fingers and attempt to pull them apart
as vigorously as possible just as the blow is struck.
4. What effect does this muscular tension have on the reflex action? 3.5 points
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5. Explain how clenching your fists during a fight or athletic contest may affect your reflex responses.
3.5 points
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Achilles Reflex
This is a spinal reflex that results in plantar flexion of the foot.
6. Have the subject kneel on a chair, facing away from you, with the toes pointing toward the floor. Tap
the middle of the Achilles (calcaneal) tendon with a reflex mallet.
7. Describe your response. 3.5 points
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Cilio-spinal Reflex
8. Gently pinch the skin at the nape of the subject's neck.
9. Note the reaction of the pupils of his eyes. 3.5 points
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Corneal Reflex
This is a reflex mediated by the brain which involves the fifth cranial nerve.
10. Have the subject stand facing at a 90 degree angle to you. While the subject stares straight ahead,
quickly move a clean, sterile cotton ball toward the surface of one eye. Do NOT actually touch the
eye!
11. What is the reaction? 3.5 points
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12. What survival advantage does this reflex have? 3.5 points
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Accommodation Reflex
13. Examine the pupils of the subject’s eyes. Have the subject read a page in a textbook.
14. Ask the subject to glance up to look at a distant object.
15. Describe what happens to the subject's pupils. 3.5 points
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Reaction Time
Reaction time is defined as the interval between the application of a stimulus and the beginning of a
response.
16. Have the subject rest his forearm on the edge of a table with his arm with his hand projecting over
the edge. His thumb and index finger should be separated by about 1 ½ inches.
17. The observer should suspend a ruler above the hand of the subject, with the lower edge of the ruler
even with the upper margin of the thumb and finger. Make certain that the ruler is suspended with
the one inch measurement at the bottom.
18. The observer should drop the ruler without warning and measure the distance at which the subject
caught the ruler.
19. Record your results. 1.5 points
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20. Why is it so difficult to catch the ruler? 3.5 points
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21. Repeat the above step 10 times and record your results. 1.5 points
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6.
2. __________________
7.
3. __________________
8.
4. __________________
9.
5. __________________
10.
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22. Do you feel that repeated trials decreased your reaction time? Why do you feel that this occurred?
3.5 points
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CONCLUSION:
Using the data you have collected, defend the objective statement. Write your response in an essay
format on a separate sheet of paper for this section. (10 points)