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, and e.
back.

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

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

20 mm

15 mm

10 mm

5 mm

20 mm

15 mm

10 mm

5 mm

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?