"The Reflex Arc and Reflexes" In - SLC Home Page

Copyright ©2004, The School of Medicine of the University of
California, San Diego.
Laboratory Exercise – The Human Body
The Reflex Arc
adapted from: Hole, J.W. 1990."The Reflex Arc and Reflexes" In: Laboratory Manual Human Anatomy and Physiology 5 th
Edition. Wm. C. Brown Publishers:Dubuque.
OBJECTIVES:
To introduce students to some reflex responses.
To provide students with the opportunity to practice describing their observations and interpreting results.
PRELAB:
Students are expected to read and become familiar with the lab procedure. You may also find it useful to
examine the sections of your textbook dealing with reflexes as well as web resources listed on the human
bio web page http://web2.slc.qc.ca/adera/human.htm .
TESTS:
Test each of the following reflexes on one or two members of your lab team. Observe and record the
response to each reflex test.
Descriptions of the reactions should include many parameters including:
what moved? or what was felt?
intensity of movement
intensity of feeling
direction of movement
area of feeling
speed of movement
how fast did the feeling spread?
A. Triceps Reflex
Procedure: (one person)
1. Raise and support the subject’s arm so that the elbow is
at shoulder height. The arm should be completely
relaxed.
Alternatively, have the subject place their hand on their
hip. Using this position, it may be easier to illicit a reflex
but it would not be possible for the arm to actually
move.
2. Strike the triceps tendon about 5 cm above the elbow.
(Figure 1) If there is no response, repeat this procedure,
striking to either side of the original point.
3. Observe the triceps muscle for signs of movement. Ask
the subject to describe any sensations felt.
Note: the muscle contraction may not be strong enough to cause
arm movements
Figure 1. Triceps reflex test
Assignment:
1. Hand in the description of the sensations experienced by the individual tested as well as any relevant
observations. Describe what you observed. “no reflex” is not a description.
Reflexes Lab 1

Copyright ©2004, The School of Medicine of the
University of California, San Diego.
Copyright ©2004, The School of Medicine of the
University of California, San Diego.
B. Patellar Reflex (Knee Jerk)
Procedure: (two persons)
1. The subject should sit comfortably with legs hanging down over
the edge of a table (not touching the floor). The thigh muscles
should be relaxed.
2. Use the broad side of a reflex hammer to strike the patellar
tendon, just below the patella (kneecap). (Figure 2)
3. Observe the thigh muscle and record the action (if any) of the
lower leg.
Assignment:
2. Hand in the descriptions of the action observed for both
individuals tested.
3. What type of reflex is this?
4. What type of receptor is stimulated in the patellar reflex?
5. What is the effector for this reflex? Justify your response based on your observations.
Figure 2. Patellar reflex test
C. Achilles Reflex (Ankle Jerk)
Procedure: (two persons)
1. The subject can either lie down, with one knee bent crossing
the foot over the other leg, or can be seated as for the patellar
reflex test. Shoes and socks should be removed.
2. Since the subject’s ankle must remain relaxed, you will need to
hold their foot at a right angle before striking the Achilles
tendon at the back of the ankle. (Figure 3)
3. Observe the calf muscle and record the action (if any) of the
foot. Where was movement observed?
4. Wash your hands with an ethanol-based sanitizer
Figure 3. Achilles reflex test
Assignment:
6. Hand in the descriptions of the action observed for both individuals tested. Describe what you observed. “no
reflex” is not a description.
Reflexes Lab 2

Copyright ©2004, The School of Medicine of the University of
California, San Diego.
D. Plantar Reflex
Procedure: (two persons)
1. The subject should be lying down, (or seated and very relaxed) with legs in front of them and their knees
slightly bent. The thigh should be rotated so that the outer side of the foot rests on a table (or chair). Shoes
and socks should be removed.
2. Applying firm (but not painful) pressure, draw the handle end of the reflex hammer along the outside edge of
the sole, starting at the heel and ending at the base of the big toe.
3. Observe and record the movement of the toes. It may be necessary to test both feet.
4. Wash your hands with an ethanol-based sanitizer
Note: It is possible that the subject will find the procedure uncomfortable (or that it tickles). The test will not work on such individuals.
Assignment:
7. Hand in the descriptions of the action observed for both individuals tested.
8. The reaction of this reflex is that the toes either move upwards or downwards. Which response is considered
normal? (use your textbook as a guide) What would an abnormal response indicate?
E. Biceps Reflex
Procedure: (one person)
1. The subject should be seated at a table or a desk. The
elbow should be bent and the arm completely relaxed,
resting either on your arm or the subject’s own lap.
2. Gently press the biceps tendon in the antecubital fossa
with your thumb (or forefinger), and strike your thumb
with the reflex hammer. (Figure 4) Note: you should be
able to feel the thick tendon with your thumb.
3. Observe the biceps muscle for signs of movement. Ask
the subject to describe any sensations felt.
Note: the muscle contraction may not be strong enough to cause
arm movements
Figure 4. Biceps reflex test
Assignment:
9. Hand in the description of the sensations experienced by the individual tested as well as any relevant
observations.
F. Pupillary Light Reflex
Procedure: (one person)
1. Have one laboratory partner cover one eye. Briefly shine a light into the uncovered eye and observe the pupil.
Assignment:
10. Describe the change in the pupil before, during and after exposure to light.
11. Identify each of the specific components of a reflex arc within the pupillary light reflex
Reflexes Lab 3

Images from: http://medicine.ucsd.edu/clinicalmed/neuro3.htm
ASSIGNMENT (due February 18, 2009)
You are required to hand in one lab report per team. All lab reports must be typed.
Write in the past tense when describing your own work.
You are expected to work in collaboration with the other member(s) of your lab team.
Avoid quotes and, of course, copying. Answer in your own words and cite ideas from references when appropriate.
1. Hand in the descriptions of all your observations of the reflex responses. Parameters you should consider when
observing the subjects' reactions include: what moved (or what was felt), intensity, direction, and speed.
2. Provide the answers to questions posed in each of the Assignment sections.
3. Choose one of the reflex tests where two subjects were examined (knee jerk, ankle jerk, or plantar reflex) and
compare the responses of the two subjects. Your comparison should include features they have in common as
well as ways that they differ. Provide one possible reason for why the two subjects had different responses and
provide support for your idea by citing a reliable reference.
To improve your descriptions, try reading a description to someone not in the class and ask that person to “act out”
what you have described. If they are unable to repeat the movements you have described, or if their movement is
not what you expected, your description may be inaccurate or incomplete and needs to be clarified.
Sample Marking Grid
description of reactions
(0.5) what moved or what was felt
(0.5) intensity
(0.5) direction of movement or area where sensation was felt
(0.5) speed
/2 Triceps reflex (muscle twitch)
description
/8 Patellar reflex (leg kicks)
/2 description person 1
/2 description person 2
/1 type of reflex
/1 name of receptor
/2 effector
named
justified based on observations
/4 Achilles reflex (ankle jerk)
/2 description person 1
/2 description person 2
/6 Plantar reflex (toes move)
/2 description person 1
/2 description person 2
/1 normal response – defined
/1 abnormal response indicates ?
/2 Biceps reflex (muscle twitch)
description
/7 Pupillary Light Reflex
/2 description
/5 identify the reflex arc components
/7 Comparison of responses of two subjects
/2 common features
/2 differences
/3 possible reason for differences
how was choice determined? (1)
justification of choice
data (1)
reference (1)
/4 Formatting, Grammar and Style
/40 Total
Reflexes Lab 4