Materials Included In Kit

Additional Materials Required

Safety Precautions

Exercise caution when performing these activities. Do not strike your partner with excessive force when using the reflex hammer. If a reaction is not observed, try again in a slightly different location but do not hit harder. Do not throw any other objects besides cotton balls at the transparency sheets. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Disposal

All materials may be stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. Each hammer must be shared among three student groups. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the data compilation and Post-Lab Questions may be completed the day after the lab.
• All materials are reusable.
• The reflexes studied in this activity are basic tests to show the general response of common reflexes. There may be a range of normal responses among students. Atypical results should not be construed as a medical abnormality. Contact your family physician with any concerns.
• Students with especially ticklish feet may not exhibit typical results when tested for the Babinski reflex.

Teacher Tips

• Reflexes are often studied with reaction rates. Flinn Scientific also offers Measuring Reaction Time—Student Laboratory Kit, Catalog No. FB1571.

Answers to Prelab Questions

1. Describe the three continuous functions for the nervous system.

   The three functions of the nervous system are to obtain sensory neural input, integration, and motor output.

2. Some diseases affect the reflex pathways. Why might this be dangerous?

   Our reflexes are designed to protect us from harmful stimuli. If that message-to-action pathway is compromised, it could have detrimental results.

Sample Data

Answers to Questions

1. In this laboratory activity external or observable reflexes were tested. Name two reflexes that occur internally and explain how they help the body maintain homeostasis.

   Examples of autonomic internal reflexes include blood pressure, temperature regulation and water balance between cells.

2. There are many more observable reflexes in the body than were tested in this laboratory activity. Name two other observable reflexes.

   Possible answers include biceps reflex, triceps reflex, plantar reflex, brachioradialis reflex and the Hoffman reflex.

3. Provide a real life example of a time where the blink reflex might occur but is not necessary. Why does this happen?

   When driving in a car and a chunk of snow flies off of the car in front of you and hits the windshield. Although you are in no real danger as the fluffy snow will not break the window, reflexes are automatic responses our body uses to prevent harm.

4. Based on the pupillary reflex observed in this lab, describe the reason that ophthalmologists use a chemical to dilate the patient’s eyes before examination.

   When ophthalmologists examine a patient’s eyes, they often use a small light to examine the details. The papillary reflex naturally causes the pupil to constrict so that they eye is not damaged by the light. Therefore the doctor must use chemicals to counteract the reflex in order to examine the eye.

5. What do you predict would happen if the patellar reflex test is performed while standing? Explain.

   The leg would remain still because the tendon is condensed. When struck, the stretch receptors in the muscle are not activated therefore no movement is triggered.

References

Silverthron, D. Human Physiology: An Integrated Approach; Pearson Benjamin Cummings: San Francisco, CA; 2004; p. 437.

Introduction

You pick up a pan by the handle and almost simultaneously you realize it is hot and drop it. The act of letting go of the pan is a reflex. Investigate several common reflexes to learn how the nervous system works to deliver messages.

Concepts

• Reflexes
• Nervous system

Background

A reflex is a response to a stimulus that works to return the body to homeostasis. Reflexes can occur both consciously and subconsciously. An example of a conscious reflex would be quickly removing your hand from scalding water. A subconscious reflex would be the pancreas increasing or decreasing enzyme secretion in response to changes in the concentration of the enzyme.

In order to understand reflexes, it is crucial to examine the structure and function of the nervous system. The nervous system has three continuous functions—sensory neural input, integration, and motor output. Sensory neurons in skin gather external information from the environment and internal information from organs and muscles. The sensory receptors convey the information via interneurons to the central nervous system (CNS). The CNS then interprets the signal. Motor output nerves conduct the signal from the CNS to the muscle or gland cells to execute the CNS response to the original stimuli.

The simplest reflexes to study are the so-called monosynaptic stretch reflexes. Monosynaptic stretch reflexes involve only two neurons—the sensory neuron from a muscle spindle and the somatic neuron to the muscle. The knee jerk patellar reflex, biceps reflex and triceps reflex are classic examples of monosynaptic stretch reflexes (see Figure 1).

To perform a test of the knee jerk reflex, the subject sits on the edge of a table so that his or her lower legs hang freely. The patellar tendon below the knee cap is lightly struck with a reflex hammer causing the quadriceps muscle to stretch. As this muscle stretches, sensory fibers send a message to the CNS via interneurons. In response, the CNS sends a signal to the motor neurons that control the contraction of the quadriceps muscle. This signal causes the quadriceps to contract and we observe the lower leg kicking outward.

Flexion reflexes are pathways that trigger us to avoid painful stimuli such as a hot stove or sharp object. When a bare foot steps on broken glass, the pain receptors, called nociceptors, in the foot send the sensory message to the spinal cord portion of the CNS. The signal diverges into multiple interneurons. The interneurons activate motor neurons which trigger withdrawal from the painful stimulus. For safety reasons flexion reflexes will not be tested in this activity.

Experiment Overview

The purpose of this activity is to observe the innate reflexes our body performs to maintain homeostasis.

Materials

Prelab Questions

1. Describe the three continuous functions for the nervous system.
2. Some diseases affect the reflex pathways. Why might this be dangerous?

Safety Precautions

Exercise caution when performing these activities. Do not strike your partner with excessive force when using the reflex hammer. If a reaction is not observed, try again in a slightly different location but do not hit harder. Do not throw any other objects besides cotton balls at the transparency sheets. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Note: The reflex hammers are shared among all groups. Observe each reaction and record the responses on the Human Reflex Study Worksheet.

Patellar Reflex

1. Subject: Sit on the edge of the lab table with your legs hanging freely over the edge.
2. Using the reflex hammer, the experimenter strikes the tendon of the subject just below the knee cap (see Figure 2).
   {11011_Procedure_Figure_2}

Achilles Reflex

3. Subject: Sit on the edge of the lab table and remove your left shoe and sock.
4. Wearing gloves, the experimenter holds the bottom of the subject’s left foot while striking the Achilles tendon with the reflex hammer (see Figure 3).
   {11011_Procedure_Figure_3}

Babinski Reflex

5. Subject: Sit on the lab table and remove your left shoe and sock.
6. Wearing gloves the experimenter holds the subject’s ankle with his or her left hand.
7. The experimenter will stroke the heel towards the ball of the partner’s foot as shown in Figure 4.
   {11011_Procedure_Figure_4}

Pupillary Reflex

8. The subject closes one eye for one minute.
9. After one minute has passed, the experimenter should look at both of the subject’s eyes before instructing the subject to open the closed eye.

Blink Reflex

10. The subject holds a transparency sheet in front of his or her face.
11. The experimenter throws a cotton ball towards the subject’s eyes. Note: Do not throw any objects other than cotton balls at the transparency sheet!

Student Worksheet PDF

11011_Student1.pdf