Name:______________________________ Skin Anatomy & Physiology The following three experiments will have you investigate the anatomy of the skin and some of its physiology. Each group member will need a hand lens. Each group will need a black and red felt marker, a metric ruler, a calculator, and four pennies. These supplies should all be returned to the baggie when the lab is finished. Anatomy of the skin: First, using a hand lens, each lab group member should examine the skin on the back of the hand. Note the furrows and ridges. Trace some of the blood vessels lying under the skin. Try to lift the skin. Examine the skin on the palm of the hand. Note the furrows, ridges and creases. Look for moisture and calloused areas. Compare the thickness of the skin here with the skin on the back of your hand. Try to lift the skin of your palm. Record your observations. For the second data table, observe your teacher’s hand using the ProScope digital microscope. Anatomy Skin Area Observations about appearance: Back of hand Palm of hand Anatomy of hand under the ProScope Skin Area Observations about appearance: (draw a sketch too!) Back of hand: 50x Back of hand: 50x Palm of hand: 100x Palm of hand: 100x Physiology Part 1 Physiology Experiment #1: Tactile localization is the ability to determine which portion of the skin has been touched. Certain body areas are well represented with touch receptors, and stimuli can be localized with great accuracy, but other areas do not have many receptors which only allows for crude discrimination. 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 red felt-tipped markers. The “error of localization” is the measure of the distance between your initial mark and their attempted mark. Measure the error of localization in millimeters. Repeat the test in the same spot twice more, record and then calculate the average and record. Repeat the experiment on the fingertip, back of the hand, and ventral forearm and record your results. Tactile body Error of Error of Error of Average error of testing area localization localization localization localization (mm) reading #1 (mm) reading #2 (mm) reading #3 (mm) Palm of hand Fingertip Back of hand Ventral forearm Physiology Part 2 Physiology Experiment #2 - The second experiment will demonstrate that 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 called adaptation. The touch receptors adapt particularly rapidly which is highly desirable because why would we want to be continually aware of the pressure of clothing on our skin? 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. Record the time. Repeat the test, placing the coin at a different location and determine how long the sensation persists and record. After the awareness of the sensation has been lost at the second site, stack three more pennies atop the first one. If the pressure sensation returns, determine how long the subject is aware of the pressure in this instance and record. Touch adaptation time – site #1 seconds Touch adaptation time – site #2 seconds Pressure adaptation time – site #2 seconds Physiology Part 3 Physiology Experiment #3: There are different types of nerve receptors in the skin. Some receptors detect pressure. Others detect heat, cold and pain. If a student pushes the pencil point near a "cold" receptor, the point feels cool. At another site the point feels much sharper but not cold. In some areas of the skin, there is much space between the receptors. In other areas, such as skin over the lips, the receptors are bunched close together. That is why lips are very sensitive. Think about the different areas of your skin and which areas may be more or less sensitive than others. In this experiment, choose two of the four possible skin areas to use. Your options are: back of your hand, your palm, your ankle area, or your forearm. You will test your two areas for receptor sensitivity. Have your partner mark off one square-inch area in each of your two testing sites. Predict which area will have the most of each kind of receptor. Hypothesis (if, then format!!): _____________________________________________________________________________________ _____________________________________________________________________________________ Use the end of a toothpick or bamboo skewer to gently poke the skin at any point within the one inch square boundary, being sure not to break the skin. Take careful note of the sensation as your skin is being tested. Move the point of the pencil one or two millimeters in any direction and push again. Make note of the sensation. At some sites within the square inch students will detect a cold feeling. At other sites the pencil point will feel hot, pointed and painful, or there will be no sensation at all. Record your data in the table provided (use tally marks). You should test at least ten different areas within each square. Perform the activity again on the other square. Compare it to your predictions. Skin Area Being Cold? Hot? No Feeling? Tested _________________ _________________ Discussion Questions: 1. What surprised you about the way human skin looks when it is magnified fifty or one hundred times? 2. What would be an advantage to the way the skin is attached to the palm of the hand instead of how the skin is attached to the back of the hand? 3. What is tactile localization? 4. During the tactile experiment, does the ability to localize the stimulus improve with each time the experiment is done? Explain. 5. During the tactile experiment, which area has the smallest error of localization (is the most sensitive to touch)? Why do you think that is? 6. After the adaptation experiment, would you say that the same receptors being stimulated with the four coins are the same receptors stimulated with the one coin? 7. What areas of your skin are more sensitive to hot/cold stimuli? 8. Why is it beneficial to humans to have sensory receptors more heavily distributed in certain areas of the body, instead of every location being equally sensitive?
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