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Name_________________________________________________ Lab section________________ LABORATORY ONE Sensory Systems Pre-Lab Report Read through the lab manual material for this lab and refer to the material covered in the lectures on excitability and action potentials, then answer the questions below. (5 points Total). Is your ability to discriminate mechanical stimuli greater in your fingertip than in the back of your neck? Why or why not? (2 pt) What is sensory adaptation? (1 pt) What sensory stimuli in this lab show adaptation? (1 pt) In this lab we examine the sense of touch and proprioception (internal sense of force or position). Are these both forms of mechanosensory input? (1 pt) BIOLOGY 220 1.1 SUMMER 2014 LABORATORY ONE Sensory Systems Overview The ability of all living creatures to acquire, process, store and transmit information is key to their survival. Sensing environmental stimuli such as thermal, visual, chemical, or mechanical signals underlies the ability of animals to move effectively in their environment, to control the environment that they experience and to regulate their own internal environment. Indeed, animals are capable of amazing sensory feats including the ability to detect electric or magnetic fields, see The fly is a Laphria grossa (a species of Bee-like visual signals in infrared or ultraviolet wavelengths, detect Robber Flies, Gen. Laphria) from Florida. Photo is a composite of 11 individual macro images with very minute concentrations of chemicals or hear (and produce) limited depth of field, merged together to create an extended focus image by Armin Hinterwirth sounds at ultra-high frequencies. All of that sensing underlies communication, regulation, and much more. In this lab we will use a model organism (the human) to explore: How does the distribution of sensory neurons reflect functional requirements for sensing? How do sensory neurons adapt to a stimulus and what are the consequences of adaptation? In addition, we can use data derived from all members of the class to ask broader questions about the variation in human sensory performance. (How variable is our ability to sense mechanical stimuli? Does age or gender matter?) _________________________________________________________________________________________________________________________________________________________________ I. Receptive fields: two point discrimination and tactile localization. In all animals, mechanical information (touch, pressure, pain) is converted into neural signals by a vast array of mechanosensory neurons whose dendritic endings respond to mechanical forces via stretch sensitive ion channels. Many of these channels provide a passage for positive ions, depolarizing neurons to a threshold where action potentials may be generated. In humans (we will use them for our study animals in this lab) as in all other animals, the distribution of mechanosensory cells is extremely uneven. In some areas, these cells are densely distributed over the surface, whereas others have far fewer dendritic endings. That unevenness reflects the functional roles played by different parts of your body. Interestingly, the number and density of neurons is also reflected in the fraction of the brain associated with processing sensory information. Regions with many neurons (e.g. fingers or lips) have large fractions of your brain designated for those areas. Others body regions, with far fewer neurons innervating the surface, have much less brain area devoted to them. BIOLOGY 220 1.2 Figure 46.21 SUMMER 2014 EXPERIMENT 1: Two-Point Discrimination and Distribution Touch receptors are distributed unevenly across the body. Some regions have dense distribution while others have sparse distribution. Two-point discrimination is a simple way to determine densities across various areas of the body. 1.) Beginning with calipers set to a distance of 80mm, and the subject’s eyes closed, touch the dorsal (back) side of the subject’s hand and ask her/him to report if one or two points are sensed. 2.) Repeat this procedure while reducing the caliper settings by 10mm increments until only one stimulus is perceived. While doing so, touch your partner’s hand with only one caliper tip at random intervals. This will prevent your subject from guessing what stimulus will be applied. 3.) Record the distance at which only one stimulus is perceived (Table 1). This is known as a critical point. 4.) Continue this experiment for the other parts of the body: palm of hand, index fingertip, forearm (non-hairy, ventral surface), upper arm (outer surface), shin, back of neck. Note that some of the more sensitive areas of the body may display a very small critical point. In such instances, use smaller spacing intervals when decreasing the spread of the calipers, such as 1mm. TABLE 1 Region Back of hand Palm of hand Index finger tip Upper arm Inner Forearm Shin Back of neck Other Distance (mm) QUESTIONS 1.) Discuss how two-point discrimination varies with region. 2.) Suggest how two-point discrimination might reflect the functional demands of those regions for mechanosensory input. EXPERIMENT 2: Tactile Localization Tactile localization is the perception of a stimulus at a specific location on the body. Like two-point discrimination, it reflects the density of neurons innervating particular regions. Here, however, we have the task of recreating where we detected a sensory stimulus. Precision of locating the stimulus origin is associated with stimulus intensity as well as receptor density at the stimulus location. Since receptors are not distributed evenly across the dermis, different parts of the body have different capacities to locate the stimulus. 1.) Use the non-dominant arm as the marking arm. Have the subject close his/her eyes during this test. The subject will sit relaxed with one arm resting on the table, palm up, with the other hand resting on the arm above the elbow. 2.) Using a pen that will leave a mark on your subject’s palm (such as a permanent marker), touch a point on the subject’s palm. Be sure to be as consistent as possible with the pressure you use on the pen. BIOLOGY 220 1.3 SUMMER 2014 3.) Give the pen to the subject and have her/him attempt to touch the spot where the initial touch was made, using his/her dominant arm. Make sure his/her eyes remain closed. 4.) Measure and record the distance between the two marks (Table 2). 5.) Repeat this test 2 more times for each body region listed in Table 4, marking in a different area each time. Calculate the average distance for each body region. 6.) Create a figure that sequentially shows the distance error in each of the 3 trials for each body region. Include data for each of the 3 body regions on one figure. TABLE 2 Trial Palm of hand error (mm) Fingertip error (mm) Inner forearm error (mm) 1 2 3 mean QUESTIONS 1.) Does the error of localization vary with the region? How? Discuss why. 2.) Based on your results from the prior experiment, does the error of localization vary in a similar manner as your ability to discriminate two points? Why or why not? 3.) Does learning or experience modify the accuracy of localization? 4.) What neural disorders might you diagnose using either of these two experiments? EXPERIMENT 3: Tactile Localization and Stimulus Intensity As mentioned above, both the intensity of the stimulus and the density of neurons determine your ability to localize a stimulus. (1) Develop a hypothesis for how you think the intensity of the stimulus will determine your ability to localize that stimulus. Using the same protocol as in Experiment 2, fill out the table below. You should feel free to use any reasonable region of the body (palm, arm, leg). Please indicate the region have selected. TABLE 3 Region____________________ Trial Lighter touch to region (mm) Heavier touch to region (mm) 1 2 3 mean BIOLOGY 220 1.4 SUMMER 2014 EXPERIMENT 4: Adaptation to a mechanical stimulus The experiments above may be confounded by the ability of sensory neurons to adapt to the stimulus you delivered. Many sensory receptors respond strongly to acute changes in the environment and cease responding when the stimuli become constant. This phenomenon is known as sensory adaptation. For example, our sense of smell quickly adapts to the odors of the laboratory, while our touch receptors soon cease to inform us of our clothing until these stimuli change. Here we will focus on three sensory adaptations. In this simple experiment we are mimicking the “clothing effect” where our sense of a mechanical stimulus fades in time. 1.) Place a cork on the back of your partner’s hand and measure the time required for the initial sensation from the pressure of the cork to abate. 2.) Repeat an additional 2 times and calculate the average time. TABLE 4 Trial 1 2 3 Mean Time (s) QUESTIONS 1.) Is there much variability in recognition time among trials? Explain. 2.) How does adaptation correlated with receptor density, if at all? 2.) What are some evolutionary advantages of sensory adaptation? Disadvantages? EXPERIMENT 5: Adaptation to a thermal stimulus The experiments above focused on detecting external mechanical stimuli. Sensory systems can also encode thermal stimuli and, like the responses to mechanical stimuli, can show adaptation. In this experiment, you will explore adaptation to thermal stimuli. 1.) Fill two plastic beakers with water, one with cold tap water, and one warm water (approximately 45 C) from the hot water faucet. Fill the larger container with room temperature water (approx. 25 C). 2.) Place your left hand in the cold water and the right hand in the warm water. Wait 1 minute. 3.) Place both hands in the larger container filled with room temperature water and then fill out the responses below. Left hand estimate of water temperature ______ Right hand estimate of water temperature ______ Actual temperature of cold water ______ Actual temperature of warm water ______ QUESTIONS 1.) What are the consequences of sensory adaptation? Can it be permanent? Why or why not? 2.) What do you think would happen if you followed steps 1 and 2 above and then waited 5, 10, or 15 minutes before placing your hands in the room temperature water? BIOLOGY 220 1.5 SUMMER 2014 EXPERIMENT 6: Adaptation to mechanical (proprioceptive) stimulus. The experiments above focused on detecting external mechanical or thermal stimuli. Mechanosensory systems also detect how our bodies are configured. This ability to ascertain our body configuration is called “proprioception” and provides sensory information that is crucial in posture control, locomotion, manipulation and dextrous hand control. Proprioceptors in skeletal muscles provide information about the effort exerted by various movement tasks such as grasping, walking or dancing. Thus, in contrast to the above experiments, proprioception is a measure of internal mechanical forces and positions, as opposed to external stimuli. Our brain integrates information from proprioceptors and from our vestibular system (the inner ear) to control body movements. Proprioception is used in a standard field sobriety test to check for alcohol intoxication. In that test, the subject is required to touch his or her nose with eyes closed. People with normal proprioception may make an error of no more than 20 mm. People with alcohol impairment fail this test due to difficulty with proprioception. EXPERIMENT 6A SOBRIETY TESTING With your eyes closed, place your index finger at the center of the tip of your nose. Have your lab partner measure the error. Repeat this three times for each hand. Right hand Distance (mm) _____ ______ _____ Average distance (mm) ______ Left hand Distance (mm) _____ ______ _____ Average distance (mm) ______ QUESTIONS 1.) Which hand is dominant for you? 2.) Does hand dominance determine precision of proprioception? EXPERIMENT 6B JOINT POSITION MATCHING. Joint position matching (JPM) is an established protocol for measuring proprioception, and joint position sense specifically, without the aid of visual or vestibular information. During such tasks, individuals are blindfolded while a joint is moved to a specific angle for a given period of time, returned to neutral, and the subjects are asked to replicate the specified angle. Measured by constant and absolute errors, ability to accurately identify joint angles over a series of conditions is the most accurate means of determining proprioceptive acuity in isolation to date. Recent investigations have shown that hand dominance, participant age, and presentation time of the angle can all affect BIOLOGY 220 1.6 SUMMER 2014 performance on joint position matching tasks. Joint position matching has been used in clinical settings in both the upper and lower extremities. Keep your eyes closed throughout the whole experiment. 1.) With your body in a relaxed state, have your lab partner position a joint at an angle. 2.) Have your lab partner measure that angle and then return your joint to its initial state. 3.) Repeat this three times, filling out the table below. TABLE 5 Joint____________________ Trial Positioned angle (degrees) Returned angle (degrees) 1 2 3 mean Calculate the mean difference between the Positioned angle and Returned angle _________ BIOLOGY 220 1.7 SUMMER 2014