Name____________________________________________________Section________________Date___________Week 7: Sensory Abilities

Name____________________________________________________Section________________Date___________

Week 7: Sensory Abilities

Invitation to Inquiry

There are many kinds of eye-glasses used for special purposes. People who fish like to wear polarizing sunglasses. People who shoot guns competitively, typically wear amber colored glasses. Conduct some research to determine why each prefers a particular kind of eye-wear.

Background

This laboratory exercise gives you an opportunity to study how we sense changes in our surroundings. Your ability to sense changes in your surroundings involves (1) the specific ability of sense organs to respond to stimuli (detection), (2) the transportation of information from the sense organ to the brain by way of the nervous system (transmission), and (3) the decoding and interpretation of the information by the brain (perception). In order for us to sense something, all three of these links must be functioning properly. For example, a deaf person might be unable to detect sound because (1) there is something wrong with the ear itself, (2) the nerves that carry information from the ear to the brain are damaged, or (3) the portion of the brain that interprets information about sound is not functioning properly. While this laboratory activity focuses on the function of sense organs, it is important to keep in mind that the peripheral and central nervous systems are also important in determining your sensory ability. All sense organs contain specialized cells that are altered in some way by changes in their environment (stimuli). The sensory cells depolarize and since they are connected to nerve cells, they cause the nerve cells to which they are attached to depolarize as well, and information is sent to the brain for interpretation by way of nerve pathways.

In this lab exercise you will:

1. Make a map of the location of different kinds of taste buds on your tongue.

2. Determine several characteristics of the sense of “touch.”

3. Locate different kinds of temperature sensors in the skin.

4. Study several aspects of visual acuity.

5. Study several aspects of the sense of hearing.

Procedure

Taste

Taste involves several different kinds of sensory cells located on the tongue and pharynx. Each kind of sensory cell responds to specific kinds of chemicals. So there is not just one sense of taste; there are several. We recognize at least five different kinds of taste senses: sweet, sour, salty, bitter, and umami (meaty).

Mapping the Sense of Taste on the Tongue

1. Work with a lab partner.

2. Obtain a cotton swab and dip it into one of the solutions. The solutions are labeled sweet, sour, salt, bitter, and umami (meaty).

3. Have your lab partner touch the swab to the tongue at the following five locations: a. the tip, b. right side, c. left side, d. center, ande. back.

Place an X on the following drawings of the tongue to indicate where you detected each chemical.

a

a

A

a

a

c

d

b

d

b

D

b

d

b

d

b

c

c

c

c

e

e

E

e

e

Sweet

Sour

Salt

Bitter

Umami

4. Test the other four solutions in the same manner, but be sure to rinse your mouth with water after each solution.

5. When you have tested each of five chemicals, switch positions with your partner.

Results

1. Can you detect each chemical at all places on the tongue?

2. Compare your results to your partner and other people in class. Do they detect the same chemicals in the same place?

3. What does this tell you about the sense of taste?

The Role of Solubility in Detecting Taste

1. Dry off the tip of your tongue with a clean paper towel. Place a few grains of table salt (NaCl) on the tip of your tongue. Record the time interval from the time you place salt on the tip of your tongue until you first taste the salt. __________

2. Dissolve a few grains of salt in a small amount of water. Place this on the tip of your tongue. Record the time interval from the time you place the salt solution on the tip of your tongue until you first taste the salt. __________

Were the two time intervals different? What does this tell you about the ability to taste salty materials?

Touch

The sense of touch is made up of a number of different types of receptor organs. Pressure, pain, heat, and cold are all aspects of the sense of touch. We will experiment with some of them here.

Localization of Touch

You need a partner for this exercise.

1. The subject should keep his or her eyes closed throughout the exercise.

2. Touch the skin on the back of the hand of the subject lightly with the pointed end of a soft lead pencil. Be sure to leave a mark.

3. Then ask the subject (with eyes still closed) to use a blunt probe to locate the place on the skin where the stimulus was received.

4. Use a ruler to measure as closely as possible the error in locating where the stimulus was applied. Measure the error in millimeters. Repeat five times at different locations on the back of the hand.

5. Change roles with your partner and repeat the experiment.

Results and Conclusions

In the space provided, write a short paragraph that states your findings and conclusions.

Density of Sense Organs

You need to work in pairs.

1. Have the subject keep his or her eyes closed.

2. Use a pair of forceps or calipers to gently touch the subject’s skin so that the two points of the instrument touch with the same light pressure and at the same time. Test the palm of the hand and two other regions of the body. Other regions that may be tested are the back of the hand, the tip of the index finger, the forearm, the tip of the nose, the forehead, and the back of the neck. Not all of these need to be tried, but a decent selection should be made (at least three locations).

3. Ask the subject to state whether one or two points of the instrument are felt. Repeat this procedure five times for each area of the body chosen. (To keep the subject from guessing, the experimenter should occasionally touch the skin with only one point. However, do not record the result of the response in your data).

4. Record your data in the following manner: Record a minus sign (–) whenever two points were felt as one and a plus sign (+) whenever the two points were actually felt as two.

5. Begin with the points 20 millimeters apart and systematically decrease the distance between the points from 20 mm to 15 mm to 10 mm to 5 mm. Find the smallest distance at which the subject can still distinguish two points for each portion of the body tested.

6. Change roles. Record the data made on yourself as the subject.

7. From the data, estimate the comparative densities of touch receptors of the different parts of the

body.

Area I: _____________________

distance between points of forceps in mm

Area II: _____________________

distance between points of forceps in mm

Area III: _____________________

distance between points of forceps in mm

Results and Conclusions

	Trial Number
1	2	3	4	5

20 mm

15 mm

10 mm

5 mm

	Trial Number
1	2	3	4	5

20 mm

15 mm

10 mm

5 mm

	Trial Number
1	2	3	4	5

20 mm

15 mm

10 mm

5 mm

1. What is the smallest distance the subject can still recognize two points for each of the three areas tested? Are they the same? Explain.

Sensory cell

Skin surface

Nerve to brain

2. Place a sketch of your “two-point device” on the drawing to indicate why two points are sometimes felt as one.

3. Which of the regions of the skin that you tested is represented by the left side of the drawing and which is represented by the right side of the drawing? Explain your answer.

Temperature Sense–Detecting Hot and Cold

Work with a partner.

1. With a pen, draw a square with 20 mm sides on the back of the subject’s hand, then subdivide this square into 16 smaller squares by dividing each of the sides into 5 mm segments.

2. Have the subject keep eyes closed and place his or her hand flat on the table.

3. Obtain a nail that has been in ice-cold water. Dry it off with a paper towel.

Lightly touch each of the squares of the grid on the hand at random. The subject should respond by saying “cold” if such a sensation is actually felt; otherwise the subject remains silent. It is important for the subject to ignore the sense of touch and concentrate on the sensation of cold.

4. For every positive response, the experimenter marks a plus sign (+) on the following grid at a point corresponding to the point tested on the skin.

5. Be sure that the nail is really cold when you make each test.

6. Repeat this exercise with a very warm nail and record your results on the second grid.

Cold Warm

7. Switch roles with your partner and repeat the exercise.

8. Answer the following questions.

Do you detect hot in every square?

Do you detect cold in every square?

Are hot and cold receptors always located in the same squares?

Do the same receptors respond to hot and cold? Explain how you know.

Temperature Sense—Detecting Changes in Temperature

1. Dip one finger into a beaker of hot water and at the same time put a finger from the other hand into cold water.

2. After 30 seconds, transfer both fingers into a third beaker of warm water.

Results and Conclusions

Describe the sensations of both fingers in the beaker of warm water and explain why there is a difference in sensation.

Vision

The eye is a complex structure that focuses light on cells of the retina that respond to changes in light. There are two kinds of light receptors; rods and cones. Rods are very sensitive to light and only respond to differences in light intensity. The cones are less sensitive to light. There are at least three kinds of cones, each of which responds to specific colors of light. The rods and cones are located in different places in the retina of the eye. In this part of the lab activity you will make a number of observations about the eyes and their response to various stimuli.

Determining the Location of Rods and Cones

Rods and cones are not located in the same place on the retina of the eye. When you look at things from directly in front of the eye, the cornea and lens of the eye focus the light on a region known as the fovea centralis. When you look at things with your peripheral vision, the light is focused on regions of the eye other than the fovea centralis.

Work with a partner.

1. Choose three similarly colored squares of paper about 100 cm by 100 cm.

2. Have your partner stare at a distant object directly in front of him or her.

3. Start behind your partner (out of the field of vision) and slowly move the piece of paper forward at eye level about 30 cm to the side of the head.

4. Ask your partner to tell you when the piece of paper is first seen and when the color of the paper can be detected.

Use the information about the location of rods and cones and the results you just obtained to answer the following questions.

Which sense organs (rods or cones) are most common in regions outside the fovea centralis?

Which sense organs (rods or cones) are most common within the region of the fovea centralis?

Explain how this experiment allows you to answer these questions.

Detecting the Blind Spot

Use the + and dot below in the following manner. Close your left eye. Place the page close to your face. Stare at the + with your right eye. Slowly move the page away from you. What happens to the dot?

+	•

In order to detect the presence of an object, light must fall on the retina of the eye and stimulate either rods or cones. There are no rods or cones at the point where the optic nerve goes

out of the back of the eye. Use this information to explain what you observed when looking at the + and • above.

Hearing

The sense of hearing involves the detection of sound vibrations. Airborne sounds cause the eardrum to vibrate. The eardrum is attached to a series of three small bones: the malleus, incus, and stapes. The stapes is attached to a membrane over a small opening in the cochlea. The cochlea is fluid filled. Thus, the vibrations of the air are transferred to the fluid of the cochlea. When the fluid in the cochlea vibrates, cells in the cochlea are stimulated. When these cells depolarize, they send a signal by way of the auditory nerve to the brain. In this part of the lab activity we will explore some aspects of hearing.

Work with a partner.

1. Strike a low frequency tuning fork (100 cps) and hold it near one ear. Determine how far from the ear the subject can hear the tuning fork. Repeat with the other ear. Are both ears the same?

2. Strike the tuning fork and touch the base of the vibrating tuning fork to the skull just in front of the ear. Does the volume change?

How is this sensation of hearing different from when the base of the turning fork touches the skull near the ear?

3a. Have the subject sit with closed eyes. Strike the tuning fork.

Have the subject point to the position of the tuning fork. Repeat three times from different positions.

Can the subject correctly identify the position of the tuning fork?

3b. Now have the subject keep eyes closed and plug one ear with a finger.

Have the subject point to the tuning fork as it is struck at different positions. Was the subject able to locate the position of the tuning fork accurately? Why was there a difference between the two different trials?

Sensory Abilities

Name ___________________________________________ Lab Section____________________

Your instructor may collect these end-of-exercise questions. If so, please fill in your name and lab section.

End-of-Exercise Questions

1. Describe the regions of your tongue that are most sensitive to sweet, sour, salt, bitter, and umami.

2. How is solubility important to the sense of taste?

3. Determine the average distance between points on the palm of the hand at which persons in the class correctly identified that they were being touched by two points. On the average, individuals

could discriminate between two points that were _____ mm apart.

4. Using the data you collected for different parts of the skin, rank them according to which had the greatest density of touch receptors and which had the lowest density.

5. Write a paragraph describing what you learned about the receptors that respond to temperature. How many kinds of receptors are there? Explain how you know there are different kinds of receptors.

6. There are some kinds of people who can see well in bright light but are not able to see in dim light. This condition is called “night blindness.” What kinds of sensory cells do not function to capacity in individuals who have night blindness?

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