Touch Receptors and Mapping the Homunculus Name: Date: Class: INTRODUCTION Humans learn a great deal about their immediate environment from the sense of touch. The brain is able to determine where the body has been touched and often can identify what the object is. Some areas of the skin have more touch receptors in a given area than others. MATERIALS Metric ruler Graph paper Rubber stopper with pins SAFETY PRECAUTIONS Gently apply the pointed objects to the skin. Disinfect the rubber stopper with pins points as directed by your teacher before using on another individual. PROCEDURE 1. Gently place the two points of the rubber stopper with pins on your lab partner's skin and determine if they can feel one or two points. 2. Move the pins in the rubber stopper closing the gap between the pins and repeat the activity. Continue in the same area of skin until your partner can no longer identify two separate points. Record this distance on the data table. 3. Test both the left and the right side of the body. Make sure that your partner is not looking as the skin is touched. Test only those areas indicated by your teacher. Check the reliability of the responses by randomly touching with only one point. 4. Calculate the reciprocal value of each measurement as an estimate of the number of touch receptors in the skin of that area. The higher the reciprocal number the more touch receptors in that area. Types of clothing may affect which of the following you are able to complete. Do the best you can to complete testing on as many areas as possible.
Two Point Discrimination Test Results Body part Left Side Measurement (cm) Reciprocal (1/measurement) Right Side Measurements (cm) EXAMPLE 2 ½ = 0.5 1 1/1 = 1 Scalp Forehead Cheek Nose Upper lip Lower lip Chin Front of neck Back of neck Upper back Shoulder Upper arm Elbow Forearm Wrist Back of hand Palm of hand Tip of thumb Tip of index finger Tip of third finger Tip of fourth finger Tip of fifth finger Front of thigh Back of thigh Front of lower leg Back of lower leg Top of foot Bottom of foot Big toe Second toe Third toe Fourth toe Fifth toe Reciprocal (1/measurement)
Touch Receptors and Mapping the Homunculus Name: Date: Class: Choose 6 tested areas from various locations and graph the results. Differentiate between the right and left side data by color coding all the bars of the right side with one color and all the bars of the left side with another color. Right and left side data for a particular area should be shown side by side. # of Touch Receptors per cm
Analysis 1. Of the parts of the body tested, which part was best able to distinguish between the closest stimuli? 2. Which part was least able to distinguish between the closest stimuli? 3. What do your results infer about the distribution of touch receptors in the skin? 4. How did the number of touch receptors on the right side compare to the number on the left side? What do you think is the reason for these results? APPLICATION: Homunculus means little person. Usually resembles a cartoon character. 1. Using the 2 nd piece of graph paper draw a homunculus which would represent the data you collected during your experiment. Draw your homunculus in the correct anatomical position. Make the area of the body large if it has more receptors or smaller if it has fewer receptors. Use the graph paper with large squares only as a guide to the relative sizes of the body structures. It is NOT necessary to measure exactly on the graph paper. It is important to show the relationship between the various areas of the body. That which has the most receptors is the largest and that with the least is the smallest on the drawing.
APPLICATION QUESTIONS: 1. Hypothesize how your human homunculus might differ from other mammalian species. Discuss how these differences might indicate some of the adaptations in that animal. 2. The area in the brain where stimuli from touch receptors are interpreted is called the somatosensory cortex. On the cerebral cortex diagram below: Determine the anatomical plane by which the cut was made. Use this information to create a title for the picture. Label the superior and inferior areas Label the appropriate area on the diagram with the name of the body part from which sensory input would be interpreted. (internet will be very helpful here)
Homunculus Drawing of (Student s name)