BIOL 2401
Sensory Systems
Objectives
After completing this lab, you should be able to:
1. Identify taste buds and describe their functions
1. Describe the location of the 4 taste modalities on the tongue.
2. Identify & describe the function of the major eye structures in the human eye.
3. Explain what is the “blind spot” of the eye.
Materials
Your AP Textbook
Human eye model
Taste Buds slide
Sweet, sour, bitter and salty favors
Sterile cotton-tipped swabs
Blind spot determiner
Dixie cups
INTRODUCTION
Sensations occur in the central nervous system (CNS) after sensory stimuli (e.g. touch,
smell, pain, temperature, etc.) in the internal or external environment are detected by
sensory receptors that convey the information to the CNS. There are five types of
sensory receptors in the body. However, each one is stimulated by a specific kind of
stimulus and much less sensitive to other forms of stimuli. Senses mediated by sensory
receptors can be classified into two major groups: general senses and special senses. The
general senses are the sense of touch, pressure, temperature, and pain. The sensory
receptors for the general senses are widely distributed in the body and usually found in
skin, muscles, joints, and viscera. Special senses are the sense of smell, taste, sight,
hearing and equilibrium. The sensory receptors for the special senses are found in
sensory organs in the head (e.g. eye, nose, ear, and tongue).
All senses work similarly: a sensory receptor (a specialized cell) in the peripheral
body is stimulated by a specific stimulus. This sensory receptor then stimulates a neuron
that then sends nerve impulses to the cerebral cortex of the brain. At the cerebral cortex
then a perception of the stimulus is formed.
Define:
Sensation: _______________________________________________________________
________________________________________________________________________
Perception: ______________________________________________________________
________________________________________________________________________
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In this laboratory exercise, you will explore the distribution of some somatic sense
receptors associated with the skin and special sense receptors for taste and vision. You
will also locate and identify the structures of the eye by viewing a human eye from a
cadaver by using your Anatomy & Physiology Revealed, Version 2.0, CD.
Procedure
General Senses
PART 1
Meissner’s Corpuscles – Sensory receptor at the superficial dermis.
1. Observe the Meissner’s corpuscle slide already set up in the microscope. Sketch a
representative diagram of the Meissner’s Corpuscle in the following space.
Meissner’s Corpuscle (____X)
Meissner’s Corpuscle
2. Answer the following questions about Meissner’s corpuscles.
a) List body parts where Meissner’s corpuscles are found.
________________________________________________________________________
________________________________________________________________________
b) What type of sensation do Meissner’s corpuscles detect?
________________________________________________________________________
Pacinian Corpuscles – Sensory receptors at the deep dermis.
1. Observe the Pacinian corpuscle slide already set up in the microscope. Sketch a
Representative diagram of a Pacinian Corpuscle in the following space.
Pacinian Corpuscle
Pacinian Corpuscle (_____X)
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2. Answer the following questions about Pacinian corpuscles.
a) List body parts where Pacinian corpuscles are found.
________________________________________________________________________
________________________________________________________________________
b) What type of sensation do Pacinian corpuscles detect?
________________________________________________________________________
PART 2
1. In this activity, you will explore the distribution pattern of touch receptors in your
laboratory partner’s skin. Do the following steps:
a) Using a washable marker, draw a 2.5 cm (1 inch) square on the skin of your lab
partner’s inner wrist, near the palm. Divide the square into smaller squares with 0.5 cm
on a side, producing a small grid.
b) Have your partner rest the marked writs on the tabletop and to close his or her eyes
throughout the experiment.
c) Touch the tip of the bristle in some part of the grid just hard enough to bend it slightly.
d) Ask your partner to report whenever the touch of the bristle was felt. Mark the
position on the matching grid below. Record “0” if your partner does not feel the touch;
record “+” if your partner does feel the touch. Repeat this test in 25 different locations on
the grid.
Move randomly through the grid to prevent anticipation of the next stimulation area!
e) Repeat this test in the same manner on two other different areas of exposed skin.
Record your results below and compare the density of touch receptors in these areas.
Skin of wrist
Area tested ____________
Area tested ____________
2. Answer the following questions:
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a) Are the touch receptors evenly distributed over the skin’s surface?
Yes
No
b) Describe how concentration of touch receptors seems to vary from region to region.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
PART 3
Two-Point Discrimination Test
The Two-Point Discrimination test is done to test the ability to recognize the difference
between one and two points of the skin being stimulated simultaneously.
1. Follow these steps to do the two-point discrimination test:
a) Ask your lab partner to place his or her hand with the palm upward on the lab table and
to close his or her eyes during the experiment.
b) Hold the tips of a forceps tightly together and GENTLY place the tips of the forceps on
the skin of your partner’s index finger.
c) Ask your lab partner to report if it feels like one or two points are touching the finger.
d) Move the forceps points apart by about 1 mm and touch the skin of the index finger
again. Ask your lab partner to report as before.
e) Repeat this sequence, each time increasing the distance between the forceps tips
slightly until your partner tells you that two distinct points are felt. The minimum
distance between the tips of the forceps when both can be felt is called the two-point
threshold. When the two-point threshold is felt, two separate touch receptors are being
stimulated simultaneously instead of only one receptor.
f) Record the distance between the tips of the forceps when the two-point threshold was
detected.
e) Repeat the test and determine the two-point threshold of the palm, back of the hand,
back of the neck, and leg.
g) Record the results for the two-point threshold in millimeters for the skin in the
following areas:
Index finger ________________
Palm ______________________
Back of hand _______________
Back of neck________________
Leg _______________________
2. Answer the following questions by observing the results from your experiment.
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a) What area of the skin tested had the greatest ability to discriminate two points?
b) What area of the skin was the least sensitive to discriminate two points?
c) What conclusions can you arrive to about the significance of the results in questions a)
and b)?
Procedure
Special Senses
INTRODUCTION
The sense of taste (gustation) depends on chemoreceptors called taste buds located
mainly on the surface of the tongue. Chemicals that stimulate taste buds must be
dissolved in liquids.
Taste Buds
Fig. 1 Taste Buds: Taste
receptors on the tongue.
The sense of vision depends on photoreceptors for vision (rods and cones), located on the
inner wall of the eye. Other parts of the eye protect the eye, make it possible to move the
eye, or focus the light entering the eye. Nerve impulses produced when the
photoreceptors (rods and cones) are stimulated travel along the optic nerve to the
occipital lobe of the brain, which interprets the impulses and produces the sensation of
sight.
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Sense of Taste (Gustation)
PART A: Taste Buds are the Taste Receptors for Gustation
1. Obtain a Taste Buds slide and view it under the microscope. Start at the 10X lens and
focus the image. Once the image is in focus, view the taste buds at the 40X lens.
Study Fig. 1 in this lab handout. Then draw and label taste buds:
Draw
taste buds
?
1. List three places where taste buds are located. ________________________________
_____________________________________________________________________
PART B: Mapping The Distribution of Taste Modalities On The Tongue
PROCEDURE: A partner is required for this exercise.
*Please read these instructions first before the start of your experiment.
*Remove gum or other food from your mouth and rinse your mouth with water.
1. List the five primary taste modalities:_______________________________________
______________________________________________________________________
2. Taste buds respond to different tastes You will now map the areas on your tongue that
contain concentrations of taste buds for the different 4 main taste modalities (umami will
not be tested).You will need:
Sterile cotton swabs
Dixie cup with sugar water (Sweet)
Dixie cup with salt water (Salty)
Dixie cup with lemon juice (Sour)
Small yellow cup with bitter flavor (Bitter)
3. Map the distribution of the receptors for the primary taste sensations on your partner’s
tongue:
A) Dip a sterile cotton-tipped swab into one of the taste solutions.
B) Touch the swab on the tongue of your partner in the regions outlined on the
taste map. Tell your partner to place a plus (+) sign on the corresponding
area of his/her taste map if he/she can sense the taste. If your partner cannot
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sense the taste, have him/her place a minus (-) sign in the appropriate place on
the map.
C) After the four areas of the tongue have been tasted with one solution, discard
the swab in the Biohazard container and have your partner rinse his/her mouth.
D) Exchange roles with your partner and repeat the test with the same solution.
E) Rinse your mouth with water.
F) Repeat the procedure with each of the other three taste solutions. Be sure to
use a fresh swab for each test substance!
Taste Map – Taste Receptors Distribution.
SWEET
SALTY
BITTER
SOUR
PART C: Answer the Following Questions about Taste:
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1. Describe, using your own words, how each type of taste receptor is distributed on the
surface of your tongue._____________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
2. Describe other locations inside the mouth where any sensations of sweet, salt, sour, or
bitter were located: ________________________________________________________
________________________________________________________________________
3. How do your experimental results compare with the distribution of taste receptors
described in the textbook? Explain your answer using your own words: ______________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. Explain how does the location of the bitter chemoreceptors on the tongue relate to the
fact that some bitter foods taste strongest as they are being swallowed? ______________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
5. Internet Search: using the internet, find out information about “Umami”. When was it
discovered? What does it taste like? What does “Umami” mean? Where is this taste
detected on the tongue? In what country was this taste discovered? What foods contain
this taste? Etc. ___________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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Visual Sense
PART D: Blind Spot Detection
The optic nerve begins at the back of the eyeball. The place where the optic nerve exits
the eye is the “blind spot.” Label the “blind spot” in this figure:
Optic Nerve
Questions:
1. Why the “blind spot” of the eye is called the blind spot?
________________________________________________________________________
________________________________________________________________________
2. Name the 2 photoreceptors: _______________________________________________
PROCEDURE to detect the “blind spot” in your eye:
a) Hold the blind spot determiner (dot on the right of the cross) about 20 inches from
your face in front of your right eye.
b) Close your left eye. You should be able to see both the cross and the dot.
c) With your left eye closed and right eye focused only on the cross, slowly bring the
determiner closer to your face.
d) At a certain distance the circle will disappear from your field of vision.
Why did the circle disappear? _______________________________________
_______________________________________________________________
_______________________________________________________________
e) Try now the left eye doing the same procedure as above but focus now your left
eye on the dot.
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PART E: REVIEW The Main Structures of the Eye
1. Identification
Name this part of the eye:_________________
Function? ____________________________________
____________________________________________
____________________________________________
2. Label the following eye structures in the
figure to the right: sclera, pupil, iris.
3. Label the following eye structures in the
figure: sclera, pupil, iris, cornea.
Optic Nerve
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4. Label the following eye structures in the
figure: sclera, pupil, iris, cornea.
5. Label the following eye structures in the
figure:
cornea, lens, retina, pupil, iris
optic disk (blind spot), optic nerve
PART F: Matching eye structures with their functions.
1. Match the terms in column A with the description in column B.
Column A
a. Cornea
b. Iris
c. Optic disc
d. Retina
e. Sclera
f. Pupil
Column B
________1. White part of the eye; attaches muscles that
move the eye; protects internal eye structures.
________2. Contains visual receptors called rods & cones.
________3. Smooth muscle that controls amount of light
entering the eye.
________4. Transparent; allows images to enter the eye
________5. Passageway for light; center of iris.
________6. Beginning of optic nerve; “Blind Spot”
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