BIO 231: Human Anatomy and Physiology I
Unit 4 Lab Exercise
Remember that this is a practice lab for learning purposes only. It cannot be considered diagnostic in any
way. We don’t have the skill or training to draw any conclusions from this exercise. Also remember that
you should not touch another human being without his/her permission. Always ask your reflex partner —
Is it OK if I do this?
Purpose
This lab will demonstrate the functions of cranial and spinal nerve reflexes. You will be able to


Define the terms reflex and reflex arc.
Identify the components and diagram particular arcs to demonstrate the function of each
component of reflex arcs.
Explain the importance of reflex testing in a clinical setting.

Directions
Reflex testing is important for assessing the condition of the nervous system. Abnormal or absent
reflexes can be a sign of pathology or degeneration of regions of the nervous system and can help locate
those regions. This is often the first symptom, so it’s important to find.
Reflexes are characterized in a couple of different ways:
By the division of the nervous system in which they occur

Autonomic reflexes are mediated by the autonomic nervous system and are not subject to
conscious control.
Somatic reflexes are mediated by the somatic or voluntary nervous system.

By the number of synapses involved in the reflex

monosynaptic — one synapse. The synapse occurs between one sensory neuron and one
motor neuron.
polysynaptic — more that none synapse. Most reflexes are polysynaptic

For this experiment you’ll need some materials, skills and directions.
Materials:

A friend! Please recruit someone who is willing to test your reflexes and let you test theirs.

A heavy wooden spoon, rubber handle of spatula or another creative tool to use as a reflex
hammer. If you have access to a reflex hammer, please use that.
A straight chair
A ruler or yardstick, preferably marked in centimeters. If you don’t have one marked in
centimeters, remember that 2.54 centimeters = 1 inch.
A calculator (unless you are really good with square roots)



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BIO 231: Human Anatomy and Physiology I
Skills: The ability to follow directions.
Reference:


View Section 3-5-2, Overview of the Neurological Exam, in the Open Book: Anatomy and
Physiology. If you downloaded a PDF version of the book, you can find the section in Unit 3:
Chapter 16, 16.1.
View the YouTube video, Neurologic Exam – Reflexes and Clonus [Duration: 5:42],
https://www.youtube.com/watch?v=5c8UJnNHa44. View the entire video. A brief look at
reflexes begins at 4:06.
Directions and Activities
Part I
Draw a monosynaptic reflex arc. Draw a polysynaptic reflex arc. On both label and annotate the
components of the arc.
Part II
There is a list of directions to elicit particular reflexes below. As you do them remember to perform them
on each side — so elicit one response and then it's contralateral counterpart immediately and note any
discrepancy.
For each reflex use this common scale to rate your observations:
0 — no reflex was elicited; the reflex is absent.
1 — weak, trace reflex.
2 — normal reflex.
3 — more ’brisk’ than normal.
4 — clonus (a repetitive or vibratory movement) is observed but not sustained. Reactions may
be observed in associated and/or contralateral muscle groups.
5 — sustained clonus.
Using the scale above rate each reflex and enter the data into the appropriate data table.
Identify the components of the arc.
Test
Patellar Reflex
Left Side
Right Side
Where are
the sensory
neurons
Dorsal Root
Ganglion L2L4
Patellar Reflex
with book
Patellar reflex
with fatigue
Achilles’ (Calc
aneous) Reflex
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What muscles
produced the
response?
Describe
the
response
Remarks
BIO 231: Human Anatomy and Physiology I
Triceps Reflex
Biceps Reflex
Dorsal Root
Ganglion of
C7
Dorsal Root
Ganglion of
C5 - C6
Activity 1 - THE PATELLAR TENDON REFLEX
A. The patellar tendon reflex or knee-jerk reflex is a monosynaptic stretch reflex that assesses the
nervous tissue between (and including) the L2 and L4 segments. Elicit it by sharply tapping the
patellar ligament just inferiorly to the patella and just superiorly to its attachment at the tibial
tuberosity.
B.
Test the effect of mental concentration on the patellar reflex by having the subject read a book
that blocks their vision of their leg. Is the response greater or lesser than above? Explain your
observations in the remarks section.
C.
Test the effect of fatigue on the patellar reflex by having the subject exercise step up and down
one stair until he/she feels tired. Don’t do this if you don’t feel capable of performing the
exercise.
Activity 2 - THE CALCANEAL REFLEX
The calcaneal reflex, aka the Achilles or ankle-jerk reflex, is a stretch reflex that assesses the nervous
tissue between (and including) the first two sacral segments. It is elicited by sharply tapping the
clacaneal (Achilles) tendon just superiorly to the ankle.
Activity 3 - Biceps Reflex
Have your reflex partner sit on a straight chair with his/her hands resting on his/her legs. Place your
thumb on the biceps tendon. Tap the first digit of your thumb.
Activity 4 - Triceps Reflex
Have your reflex partner sit on a straight chair with his/her hands resting on his/her legs. Gently hold
his or her forearm with one hand and tap the triceps tendon just superiorly to the elbow.
Part III
Testing reaction time of acquired (learned) reflexes.
A. Get a ruler or a yardstick. Hold the ruler near the end with the highest number and let it hang
down. Have your reflex partner put his or her hand at the bottom of the ruler and have them
ready to grab the ruler. They should not be touching the ruler. Tell him/her that you will drop
the ruler sometime within the next 5 seconds and that they are supposed to catch the ruler
between thumb and index finer as fast as they can after it is dropped. Record the level
(centimeters) at which they catch the ruler. Convert the distance into reaction time. Use the
following formula to calculate reaction times.
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BIO 231: Human Anatomy and Physiology I
𝑡= √
2𝑦
𝑔
In the formulas, t = time (in seconds); y = distance (in cm); g = 980 cm/sec2 (acceleration due to
gravity).
Record the reaction time in seconds in the data table.
Test the same person 5 times (vary the time of dropping the ruler within the 5 second time
period so the other person cannot guess when you will drop the ruler.
B.
Repeat the above experiment but this time say a simple word each time you release the
ruler. Select a specific word as the signal to catch the ruler. Say a lot of different words, but
direction your reflex partner to only catch the ruler on the signal word. On all other words he or
she should let the ruler pass through their fingers. Omit trials in which the subject totally misses
the ruler. Record the distance and convert to time. Record the reaction time in seconds in the
data table.
C.
Repeat the test again to investigate the subject's response to word association. As you drop the
ruler say word, for example "cold". The subject should respond with a word that he or she
associates with the stimulus word, for example "hot" while catching the ruler. Record the
reaction time in seconds in the data table. Record the number of times the subject misses the
ruler below.
Activity: Reaction Time For Acquired Reflexes:
Trial
1
Catch Only
Catch after Signal
Catch with
word association
2
3
4
5
Mean
(sec)
What conclusions can you draw about acquired reflexes?
Submission: Submit your lab report to the Unit 4 Lab Work forum.
Grading
The lab exercise is worth 20% of your Unit 4 lab grade. You will be graded on your ability to follow the
directions of this assignment and the completeness and clarity of the lab report.
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