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Lab: Integumentary System I. Visualizing Changes in Skin Color Due to Continuous External Pressure 1. 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. 2. Color of compressed skin: _______________________________________________ 3. What is the reason for this color change? ___________________________________ _____________________________________________________________________ 4. What would happen if the pressure was continued for an extended period of time? _____________________________________________________________________ II. Determining the Two-Point Threshold The density of 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. 1. 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 by placing two toothpicks completely together. Gradually increase the distance between the two toothpicks, 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. Two-point threshold Body area tested (millimeters) Face Back of hand Palm of hand Fingertips Lips Back of neck Ventral forearm 3. Which area has the smallest two-point threshold? _____________________________ III. 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. 3. Repeat the above procedure on a fingertip, the ventral forearm, the back of a hand, and the back of the neck. Trial 1 error Trial 2 error Trial 3 error Average error Body area of localization of localization of localization of localization tested (millimeters) (millimeters) (millimeters) (millimeters) Palm of hand Fingertip Ventral forearm Back of hand Back of neck 4. Does the ability to localize the stimulus improve… The second time? _______________ The third time? _________________ Explain. _____________________________________________________________ ____________________________________________________________________ 5. Which area has the smallest error of localization (is most sensitive to touch)? _____________________________________________________________________ IV. Demonstration of 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 ahs 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. __________________________________________ _____________________________________________________________________ _____________________________________________________________________ V. Short Answer Questions Both newborn infants and aged individuals have very little subcutaneous tissue. How does this affect their sensitivity to cold environmental temperature? A 40-year-old beachboy is complaining to you that his suntan made him popular when he was young, but now his face is all wrinkled, and he has several darkly pigmented moles that are growing rapidly and are as big as large coins. He shows you the moles, and immediately you think “ABCD.” What does that mean, and why should he be concerned? Is a bald man really hairless? Explain. The epidermis is a keratinized stratified squamous epithelium. Explain why that epithelium is much better suited for protecting the body’s external surface than one consisting of a simple columnar epithelium. After studying the skin in anatomy class, Toby grabbed the large “love handles” at his waist and said, “I have too thick a hypodermis, but that’s OK because this layer performs some valuable functions!” What are the functions of the hypodermis?
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