Special Senses: Olfaction, Taste and Vision
Exercise 26, 25, 24 in the lab book
Types of Sensory Receptors
I. Chemoreceptors – detect chemical cues
Ex: taste and smell
II. Mechanoreceptors – detect stimuli via a
mechanical distortion of a cell membrane
Ex: hearing and touch
III. Photoreceptors – detect light
Ex: vision
Smell (Olfaction)
Chemoreceptors in the olfactory epithelium
respond to chemicals
Olfactory Nerve
The tongue’s surface is covered
by small projections called papillae
Papillae contain the taste buds
There are 10,000 taste buds on the human tongue
Each taste bud has ~100 taste cells
Taste Pore
Chemicals in food are detected by taste cells
located in the taste buds
Taste Cells
Taste Bud
Taste Activities
Locate the papillae on your tongue – Pg. 399
Do Activity 3: Stimulating the taste buds
Can you taste the sugar?
The Distribution of Taste
Sweet, Sour, Salty, and Bitter
There is now 5th “taste”
Umami is the distinctive taste
found in meat and cheese
Led to the creation of MSG
as a seasoning/preservative
Plotting Taste Bud Distribution
Does YOUR tongue match this pattern?
Hi, I am Kikunae Ikeda. I
discovered Umami in 1907.
You can blame MSG on me.
Taste Activities
Do Activity 4:
Effect of smell on taste
Fill out the table on Pg. 401
Do Activity 5:
Importance of taste and olfaction
on odor identification
Fill out the table on Pg. 402
Outer Ear
Middle Ear Inner Ear
Middle Ear Bones:
Malleus, Incus, and Stapes
External Acoustic
Auditory Tube
(Eustacean Tube)
Hearing involves mechanoreceptors in the ear
Sound waves vibrate the tympanum (eardrum)
Ear Infection (Otitis Media)
Inflammation of the mucosal membrane in the
middle ear
Commonly caused by bacteria from a sore throat
middle ear & throat are
connected by the auditory
Sensory Adaptation
• All senses “adapt” to stimuli
• Test with sound
The pupil will change size with light condition
The Rods and Cones
These are the photoreceptors of the eye
They occur in the retina of the eye
120 million rods and 6 million cones in each retina
Rods are specialized for low light conditions
Cones are specialized for color vision under high
light intensity
The Blind Spot
Do Activity 5: Demonstrating the Blind Spot
Why do you have a blind spot?
The Causes of Near/Far Sightedness
1. Lens over or under compensates when focusing
2. Eyeball is too long or too short for proper focusing
3. Cornea or lens has improper curvature
Lens is hard and opaque
Causes problems for focusing light on the retina
Aqueous humor is constantly being created and
drains from the eye
Blockage stops drainage, putting pressure on the
retina & optic nerve
Irregular curvature to the cornea or lens causes
focusing problems
Other vision tests:
Do Activity 8:
Binocular Vision
Testing for Astigmatism
Do Activity 10: Testing for Binocular Vision
Color Blindness
Normal Vision
Color Blind
What Causes Color Blindness?
There are 3 Types of Cones in the Human Eye:
Red Cones for red wavelengths of light
Blue Cones for blue wavelengths of light
Green Cones for green wavelengths of light
Color Blindness occurs when one or all of these
cone types are not sensitive to the correct
wavelengths of light
Occurs in 6% of men and 0.5% of women
Testing for Color Blindness
Color Blindness Test
Processing Sensory Information
• Sensory register – memory system that
records information received by receptor
cells (stored as a sensory trace)
– Specific to each sense
• Why need a sensory register?
• Size of the sensory register?
– Change Blindness Test
Dissection of the Cow Eye
Blue Book:
Yellow Book:
Pg. 368-369
Pg. 270-271
Find the structures on your handout
What is the tapetum lucidum?
Do you have a tapetum lucidum?