• Reflex lab
Advanced Biology
PURPOSE: to understand that the entire nervous system can be considered a
system of innumerable reflex arcs
MATERIALS: mallet, cotton swab, feather, 3x5 index card, textbook, ruler,
light, cotton ball , small round object, 1 candy, lemon juice
PROCEDURE: Complete the following activities and answer the corresponding
questions in each section. 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 Relfex (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, which normally would only occur when the
muscle load has suddenly increased, the muscle contracts and extends the
lower leg. Describe your results:
2. 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.
What effect does this muscular tension have on the reflex action?
Explain how clenching your fists during a fight or athletic contest may affect
your reflex responses:
Biceps Reflex
This is a spinal reflex that involves nerves C5 and C6.
Have the subject sit with the elbow flexed at about 90 degrees and palm facing
downward. Put your thumb on the biceps brachii tendon at the inside angle of the elbow
and press gently. Tap your thumb with a reflex mallet. Describe your response:
Triceps Reflex
This is a stretch reflex.
Have the subject sit in a chair, with an arm across the abdomen. Supporting the subject’s arm with the elbow
flexed at a 90 degree angle, sharply tap the posterior surface of the upper arm just proximal to the olecranon fossa
(see page in your text). Describe your response:
How might you explain this response?
Achilles Reflex
This is a spinal reflex that results in plantar flexion of the foot.
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. Describe your response:
OR: Stretch the Achilles tendon by pushing up with your left hand on the ball of the foot (extend the ankle)
• Swing the patellar hammer onto the tendon, striking it sharply.
• Measure the response by feeling the push against your left hand and observing the contraction of the calf
muscles
Uvular Reflex
1. Ask your subject to open his/her mouth widely.
2. Touch the uvula lightly with the cotton swab. What is the reaction?
How does this reflex aid in swallowing?
Cilio-spinal Reflex
Gently pinch the skin at the nape of the subject's neck. Note the reaction of the pupils
of their eyes:
Sneezing Reflex
1. Stimulate the lining of the nose with a few strands of thread or a feather. Be
careful that these items are not inhaled. Describe the results:
2. Try to inhibit this reflex by having the subject press on the upper lip just below
the nose. Describe the results you obtain:
Pupillary Reflex
This is a reflex which is mediated by the brainstem, involving cranial nerves and autonomic reflex centers.
1. Have the subject close both of his eyes for ninety seconds. Hold a 3x5 index card along the bridge of his nose so
that the right eye is shielded from the left.
2. Shine a bright light into his left eye as soon as he opens their eyes. Normally, the light receptors in the eye
receive the bright light and trigger a reflexive response by the muscles in the iris. Note the effect it has on the pupil
of the left eye: What is the advantage of such a response?
3. The right pupil may also exhibit a reflexive response, even though the light is not shown on it. This is an example
of a consensual reflex in which one side of the body responds to a stimulus applied to a corresponding organ on
the other side. Describe your results:
Corneal Reflex
This is a reflex mediated by the brain which involves the fifth cranial nerve.
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! What is the reaction?
What survival advantage does this reflex have?
Accomodation Reflex
1. Examine the pupils of the subject’s eyes.
2. Have the subject read a page in a textbook.
3. Ask the subject to glance up to look at a distant object. Describe what happens to the subject's pupils:
Static equilibrium: eyes open.
1. Lift one leg upwards with a knee bended above the waist, and hold the stance for 10 seconds.
Note if the torso is upright, if there is leaning to one side, loss of balance, or if the knee rotates.
Static equilibrium: eyes closed
1. Repeat above test, but with eyes closed. Note any differences between open and closed eyes.
.The salivary reflex:
1. Collect saliva into a graduated cylinder for 2 minutes.
2. Suck on a candy for 1 minute, then measure the saliva produced for 2 minutes afterwards.
3. Wait 3-5 minutes, then add drops of lemon juice directly to the tongue, and repeat the test.
4. Record results for each test.
Convergence reflex:
Measure the near point of convergence (NPC). This test measures the distance from your eyes to where both eyes
can focus without double vision.
1. The examiner holds a small target, such as a glass ball, printed card or penlight, in front of you and slowly moves
it closer to you until either you experience double vision or the examiner recognizes that your eyes can no longer
focus together.
2. Measure the distance from the eye at which double vision “cross eyes” occurs.