Reflex Arc Lab
Purpose: The purpose of this lab is to observe a number of different types of reflex arcs found in the human body.
Materials: 30 cm ruler
rubber reflex hammer
Procedure:
1) Patellar Reflex: Have your lab partner sit on the lab bench with their legs hanging freely. Locate the knee cap and then feel for the large tendon below the kneecap on the midline of the leg. Using the reflex hammer, strike the tendon below the knee cap. Be sure to stand to the side.
Describe the movement of the leg. Blooms = 1
2)
Now get your lab partner to stay in the same position, but this time have him/her interlock their fingers and pull with force, as shown in the figure below. While your partner focuses on pulling their arms apart, strike the tendon again with the reflex hammer.
a) Compare the movement of the leg while the subject is clenching their fingers with the movement in the previous procedure. Blooms = 2
b) This is called the Jendrassik maneuver. Research it. What response should you see when testing the Patellar reflex while performing this maneuver? What explanation does it offer for this result?
3) Pupillary Reflex: Have your lab partner close one eye for approximately one minute. Ask him or her to open the closed eye and immediately compare the size of the pupils (black circle in center of eye).
a) What happens to the size of the pupil when light hits it? Blooms = 1
b) Hypothesize what will happen to the size of your pupil when you walk into a dark room. Why is this reflex helpful? Blooms = 4
4) Reaction Rate: Ask you lab partner to place his or her forearm flat on the surface of a desk. The subject’s entire hand should be extended over the edge of the desk. Ask the subject to place the index finger and thumb approximately 2 cm apart. Hold a 30 cm ruler between the thumb and index finger of the subject (zero end down). The lower end of the ruler should be even with the top of the thumb and index finger. Without giving any warning, release the ruler within the next 30 s. Measure and record the distance the ruler falls before being caught by the subject’s thumb and finger. Do 2 more trials and take an average. Repeat the procedure for the left hand. Each lab partner should do this but you only need to record your own results.
a) Organize and record your data in a table.
b) Blooms = 1Was there any difference between the reaction rates of the right and left hand? If so, hypothesize as to why the differences occurred.
5) Achilles Reflex Have your lab partner remove their shoe and kneel on a chair so that the feet hang over the edge of the chair. Push the toes towards the legs of the chair and then lightly tap the Achilles tendon with the reflex hammer.
Describe the movement of the foot.
6) Babinski Reflex Have your partner remove a shoe and sock, sit in a chair and place the shoeless foot on another chair for support. Quickly slide the reflex hammer across the sole of the subject’s foot, beginning at the heel and moving toward the toes.
Describe the movement of the toes.
7) A student touched a stove, withdraws his or her hand, and then yells. Why does the yelling occur after the hand is withdrawn? Blooms = 4
8) The neuron is severed at point X in the picture below. Explain how the reflex arc in the above diagram would be affected.
9) Reflexes are important protective mechanisms. Explain how the blink reflex is useful in protecting the eye. What sorts of stimuli can cause the eye to blink?
10) Pediatricians often test the reflexes of infants during their regular check-ups. Many reflexes that are present at birth often subside as the baby grows and matures. Describe two infant reflexes (will have to do some research to find this).
Blooms = 4
Lab Write-Up: Your lab write-up should include:
· a title page with the names of your lab partner(s), as well as your own
· Purpose section: write the purpose of the lab in your own words
· Material & Methods section (for this lab you may say “Materials used and method followed was as stated on the lab sheet.”)
· Results and Discussion. Include the answers to the questions in complete sentences.
· Conclusion: summarizing what you learned by doing the lab.