Background reading: see chapter 6
Objectives:1. Understand the functioning of the various sensory receptors tested in lab.
2. Be able to define adaptation and referred pain and understand their presentation in lab.
3. Know the auditory pathways - air vs. bone conduction, along with the concept of localization.
4. Understand how rods and cones contribute to sight and color sensitivity.
5. Understand how taste, proprioception and temperature/touch sensitivity were tested in lab
PART I. TASTE AND SMELL
It is generally believed that there are four primary sensations of taste; sweet, sour, salty, and bitter. In spite of the limited number of primary taste sensations, we can perceive hundreds of different tastes. Therefore, the primary sensations must interact with one another to produce different tastes, much in the manner that three primary colors combine to create the visible spectrum. Even greater subtleties of flavor are created by the further integration of odor and texture.
Combined Effect of Taste and Smell.
I. Obtain several pieces (approximately 1/10 of a stick) of distinctly flavored chewing gum, such as clove, peppermint, spearmint, and juicy fruit flavors, from the center lab table.
2. Dry the surface of your tongue with a paper towel, hold your nostrils tightly shut, and close your eyes. Have your partner place a piece of gum (flavor not known to you) on your tongue. Try to identify the flavor and record your guess on the Senses Worksheet.
3. Now, still holding your nostrils shut with eyes closed, chew the gum. Record your perceived flavor sensation on the Senses Worksheet.
4. Open your nostrils and record the change in sensation.
5. Dry the surface of your tongue and shut your eyes, but do not pinch your nostrils shut. Have your partner place one flavor of gum on your tongue while holding a second flavor under your nose. Record your sensations on the Senses Worksheet.
Combined Effects of Taste, Smell, and Texture.
1. Obtain small cubes (approx 2 mm square) carrot, onion, potato, and apple.
2. Dry your tongue, shut your eyes, and pinch your nostrils shut. Have your lab partner place one of the cubes on your tongue. Attempt to identify it:
a) immediately,
b) after chewing (nostrils closed) and
c) after opening the nostrils.
Record your sensations on the Senses Worksheet.
PART II. PROPRIOCEPTORS (KINESTHETIC SENSE)
Sensory receptors located in muscles, tendons, joints, and (according to some authors) in the semicircular canals of the ear are termed proprioceptors. Sensations of position, movement, and equilibrium are the result of stretching or movement of parts where these receptors are located. The sensations are sometimes termed the "kinesthetic" senses, or the "kinesthetic" sensations. The following experiments illustrate some of these senses.
Effect of Posture and Vision on Dynamic Equilibrium.
1. Walk along a set of parallel lines with your eyes open. Record any deviation on you Senses Worksheet. Repeat this action with your eyes closed. Again note the direction and extent of deviation on your Worksheet.
2. Walk along a set of parallel lines, keeping eyes open and tilting the head toward the right side (right ear to right shoulder). Note the direction and extent of deviation on your Worksheet. Repeat this action with your eyes closed. Record your observations.
3. Walk along a set of parallel lines, keeping eyes open and the body tilted toward the right side (right ear toward right hip). Note the direction and extent of deviation on your Worksheet. Repeat this action with your eyes closed. Record your observation.
Effect of Posture and Vision on Static Equilibrium.
Note and record on the Senses Worksheet the length of time that the subject can maintain his position each of the following instances:
a) Stand on left foot, keeping the eyes open. (if subject reaches 3 minutes, they can stop and record > 3 minutes). Repeat this action with eyes closed.
b) Stand on the left foot, keeping the eyes open and the head tilted to the right side (right ear to right shoulder). Repeat this action with eyes closed.
c) Stand on the left foot, keeping the eyes open and the body tilted to the right side (right ear toward right hip). Repeat this action with eyes closed.
Location of Body Parts in Space.
1. Stand facing the whiteboard at the front of the classroom, close enough so that you can easily reach the board to mark it. Draw a small "X" on the board in front of you.
2. Place the chalk on the "X", close your eyes, raise your arm above your head, and lower your arm to try to make a mark as close as possible to the "X".
3. Repeat this procedure 2 more times.
4. Measure how far (in metric units of distance) you deviated from the "X" in each trial and record the results on the Senses Worksheet..
Effect of Vision on Manual Dexterity.
1. Write the word "physiology" in the left space on the Senses Worksheet.
2. Now with your eyes closed write the same word immediately to the right.
PART III. VISION
Negative Afterimage.
1. Place the colored flag (Figure 8 below) at a distance of approximately 1 m in front of your face in a strong light, and concentrate your gaze on the "X" for 30-45 seconds.
2. Now look at a blank white sheet of paper or a white screen. Describe what you see in the Senses Worksheet.
Fig. 8. American flag for negative after image. With apologies to Betsy Ross.
Visual Field.
1. Have the subject stand with his eyes about 30 cm from a chalkboard, cover one eye, and fix the other eye on an "X" marked on the board.
2. Have the partner move a piece of white chalk into the field of vision from various sides. Mark on the board the points at which the white object first becomes visible.
3. While the subject continues to gaze fixedly at the "X", repeat the experiment using red, green, and blue markers (or chalk), marking the points at which the colored items entered the subject's visual field.
4. Sketch the results using colored pencils or crayons on your Worksheet to represent the field for white and for the different colors.
Color Blind Tests.
Use the chart and other color blind test cards and slides, and indicate on the Senses Worksheet whether you appear to be deficient in color vision.
PART IV. HEARING
Localization.
1. Close your eyes and have your partner hold a sound source (vibrating tuning fork) in different positions near your head: in front, behind, above, and on both sides. Try to point in the direction from which you think the sound is coming.
2. Repeat with one ear plugged.
Auditory Fatigue.
1. Hold a vibrating tuning fork to one ear and as soon as you can no longer hear the sound, move it away from your ears, wait a few seconds, and bring it close to the same ear again.
2. Repeat the procedure and as soon as you can no longer hear the sound, place the handle of the tuning fork against the mastoid process of your temporal bone (big bony bump behind your ear).
Bone Conduction of Sound Waves.
1. Set a tuning fork to vibrating by striking it against the rubber triangle (NOT the lab table) and place the handle against the top of your head. Where does the sound seem to originate?
2. Repeat with one ear closed. Where does the sound seem to come from now?
3. Set a tuning fork to vibrating, this time hold the tuning fork tightly against the mastoid process and compare the loudness of air conduction (holding the tuning fork next to the opening of the ear) to the loudness of bone conduction (when the tuning fork is against the mastoid process).
PART V. PAIN
A common sensory phenomenon is one which occurs when stimulation of one part of the body gives rise to sensations (frequently pain) that seem to be localized in some different or remote part of the body. Perform the following experiment to demonstrate the "referred pain" phenomenon.
1. Place your elbow in a large shallow dish of ice water and note the progression of sensation that you experience.
2. At first you will feel some discomfort in the region of the elbow. Later, pain sensations will be felt elsewhere. Where do you feel the "referred pain"? Results may very in different individuals.
PART VI. TEMPERATURE SENSATIONS
Temperature Adaptation.
1. Immerse the middle finger in a beaker of water that is not quite hot enough to elicit a pain sensation.
2. After two minutes,while continuing to hold the middle finger in the water, immerse the middle finger of the other hand into the beaker. Is the sensation the same in both fingers?
PART VII. TOUCH
Two-point Threshold.
1. Place a compass with the arms spread several inches apart on your partner's finger (palm side). Have the subject close his or her eyes. Gradually close the distance between the compass arms until the subject can no longer distinguish 2 separate points. Measure the distance between the points with a ruler.
2. Repeat the procedure on different body parts, such as forearm, lips, neck, calf muscle, and back. The points may have to be widened considerably.