Name Period Ms. Pfeil A# Activity: 1 Visualizing Changes in Skin Color Due to Continuous External Pressure Go to the supply area and obtain a small glass plate. Press the heel of your hand firmly against the plate for a few seconds and then observe and record the color of your skin in the compressed area by looking through the glass. Color of compressed skin: What is the reason for this color change? What would happen if the pressure was continued for an extended period in this area? ***There are several simple experiments you can conduct to investigate the location and physiology of cutaneous receptors. In each of the following activities, work in pairs with one person as the subject and the other as the experimenter. After you have completed an experiment, switch roles and go through the procedures again so that all class members obtain individual results. Keep an accurate account of each test that you perform. Activity: 2 Determining the Two-Point - Threshold The density of the touch receptors varies significantly in different areas of the body. In general, areas that have the greatest density of tactile receptors have a heightened ability to "feel." These areas correspond to areas that receive the greatest motor innervation; thus they are also typically areas of fine motor control. Let's check it out. 1. Using a compass, test the ability of the subject to differentiate two distinct sensations when the skin is touched simultaneously at two points. Beginning with the face, start with the compass points completely together. Gradually increase the distance between the points, testing the subject's skin after each adjustment. Continue with this testing procedure until the subject reports that two points of contact can be felt. This measurement, the smallest distance at which two points of contact can be felt, is the two-point threshold. 2. Repeat this procedure on the back and palm of the hand, fingertips, lips, back of the neck, and ventral forearm. Record your results in the chart below. 3. Which area has the smallest two-point threshold?
Activity: 3 Testing Tactile Localization Tactile localization is the ability to determine which portion of the skin has been touched. The tactile receptor field of the body periphery has a corresponding "touch" field in the brain. Some body areas are well represented with touch receptors, and tactile stimuli can be localized with great accuracy, but density of touch receptors in other body areas allows only crude discrimination. 1. The subject's eyes should be closed during the testing. The experimenter touches the palm of the subject's hand with a pointed black felt-tipped marker. The subject should then try to touch the exact point with his or her own marker, which should be a different color. Measure the error of localization in millimeters. 2. Repeat the test in the same spot twice more, recording the error of localization for each test. Average the results of the three determinations and record it in the chart below. ***Does the ability to localize the stimulus improve the second time? The third time? Explain. 3. Repeat the above procedure on a fingertip, the ventral forearm, the back of a hand, and the back of the neck. Record the averaged results in the chart above. 4. Which area has the smallest error of localization (is most sensitive to touch)? Activity: 4 Demonstrating Adaptation of Touch Receptors In many cases, when a stimulus is applied for a prolonged period, the rate of receptor response slows and conscious awareness of the stimulus declines or is lost until some type of stimulus change occurs. This phenomenon is referred to as adaptation. The touch receptors adapt particularly rapidly, which is highly desirable. Who, for instance, would want to be continually aware of the pressure of clothing on their skin? The simple experiment conducted next allows you to investigate the phenomenon of adaptation.
1. The subject's eyes should be closed. Place a coin on the anterior surface of the subject's forearm, and determine how long the sensation persists for the subject. Duration of the sensation: sec 2. Repeat the test, placing the coin at a different forearm location. How long does the sensation persist at the second location? sec 3. After awareness of the sensation has been lost at the second site, stack three more coins atop the first one. Does the pressure sensation return? If so, for how long is the subject aware of the pressure in this instance? sec Are the same receptors being stimulated when the four coins, rather than the one coin, are used? Explain. Activity: 5 Proprioception This is known as muscle sense, proprioception is the ability to sense the contraction or tension of a muscle organ. Receptors for proprioception include stretch receptors called muscle spindles and Golgi tendon organs. Can you think of any advantages to survival that this sense gives us? On the first signature line, write your name-with your eyes open, as you normally would. On the second line, write your name again-only this time keep your eyes closed. When you sign your name the second time you are mainly using proprioceptive sense. Eyes Open: Eyes Closed: Is your signature significantly different the second time? Explain your result. With your eyes open, draw a cross or an addition symbol on the white board at eye level. Now close your eyes, extend your hand out to the side, and bring it back, touch the center of the cross with the marker. Make a small mark at that spot. Now open your eyes and measure the distance from your spot to the center of the cross. Distance from center in cm.
Activity 6: Dermography: Fingerprinting As noted on page 70, each of us has a unique genetically determined set of fingerprints. Because of the usefulness of fingerprinting for identifying and apprehending criminals, most people associate this craft solely with criminal investigations. However, civil fingerprints are invaluable in quickly identifying amnesia victims, missing persons, and unknown deceased such as those killed in major disasters. The friction ridges responsible for fingerprints appear in several patterns, which are clearest when the fingertips are inked and then pressed against white paper. Impressions are also made when perspiration or any foreign material such as blood, dirt, or grease adheres to the ridges and the fingers are then pressed against a smooth, nonabsorbent surface. The three most common patterns are arches, loops, and whorls (Figure 7.8). The pattern area in loops and whorls is the only area of the print used in identification, and it is delineated by the type lines-specifically the two innermost ridges that start parallel, diverge, and/or surround or tend to surround the pattern area.
Activity 7: Taking and Identifying Inked Fingerprints For this activity, you will be working as a group with your lab partners. Though the equipment for professional fingerprinting is fairly basic, consisting of a glass or metal inking plate, printer's ink (a heavy black paste), ink roller, and standard 8 in. X 8 in. cards, you will be using supplies that are even easier to handle. Each student will prepare two index cards, each bearing his or her thumbprint and index fingerprint of the right hand. 1. Obtain the following supplies and bring them to your bench: two 4 in. X 6 in. index cards per student, Parelon fingerprint pad or portable inking foils, ink cleaner towelettes, and a magnifying glass. the bench edge and inking object. 2. The subject should wash and dry the hands. Open the ink pad or peel back the covering over the ink foil, and position it close to the edge of the laboratory bench. The subject should position himself or herself at arm's length from 3. A second student, called the operator, will stand to the left of the subject and with two hands will hold and direct the movement of the subject's fingertip. During this process, the subject should look away, try to relax, and refrain from trying to help the operator. 4. The thumbprint is to be placed on the left side of the index card, the index fingerprint on the right. The operator should position the subject's thumb or index finger on the side of the bulb of the finger in such a way that the area to be inked spans the distance from the fingertip to just beyond the first joint, and then roll the finger lightly across the inked surface until its bulb faces in the opposite direction. To prevent smearing, the thumb is rolled away from the body midline (from left to right as you see it; see Figure 7.9) and the index finger is rolled toward the body midline (from right to left). The same ink foil can be reused for all the students at the bench; the ink pad is good for thousands of prints. Repeat the procedure (still using the subject's right hand) on the second index card. 5. If the prints are too light, too dark, or smeary, repeat the procedure. 6. While subsequent members are making clear prints of their thumb and index finger, those who have completed that activity should clean their inked fingers with a towelette and attempt to classify their own prints as arches, loops, or whorls. Use the magnifying glass as necessary to see ridge details. 7. When all members at a bench have completed the above steps, they are to write their names on the backs of their index cards, then combine their cards and shuffle them before transferring them to the bench opposite for classification of pattern and identification of prints made by the same individuals.
How difficult was it to classify the prints into one of the three categories given? Why do you think this is so? Was it easy or difficult to identify the prints made by the same individual? Why do you think this was so? Tape paper with fingerprints in the space below: Activity 8: Detection of Light Touch Tactile corpuscle or Meissner s corpuscle are a type of mechanoreceptor with a nerve ending in the skin that is responsible for sensitivity to light touch. They are rapidly adaptive receptors. They are responsible to shape and textural changes. Most concentrated in thick, hairless skin and especially the finger pads. This acute sensitivity provides the neural basis for reading Braille text. You have 5 different types of sandpaper grit cut into little squares. You are to close your eyes and feel each one and put them in order from smoothest to roughest while your eyes remain closed. On the back of each sandpaper sample is a letter. Put the letters in order below from smoothest to roughest. Smoothest Roughest