The document summarizes the senses of taste and smell. It discusses how smell (olfaction) is detected by receptors in the nasal cavity that can detect up to 50 sensations. It also discusses how taste (gustation) is detected by taste buds on the tongue and palate that can detect five primary tastes: sweet, sour, bitter, salty, and umami. Both senses rely on receptors interacting with chemicals in fluids and sending signals to the brain for interpretation.

1. Taste and Smell
The Chemical Senses

2. The Chemical Senses
• Specialized to detect chemicals dissolved in a
fluid
• The fluid may be saliva, mucous, or blood
plasma
• Rely on receptors that interact with specific
molecules to generate an action potential
• Receptors are integrated with two or more
tissue types making them fit the definition of
“organ”

3. Example: G protein-coupled
receptor

4. Smell (Olfaction)
• Detected by thousands of chemoreceptors
located in the upper wall of the nasal cavities
• Receptors located in a small space about ½
square inch and are associated with other
cells to form the olfactory organs
• These receptors are capable of gathering up to
50 individual sensations which are combined
in the brain to an almost infinite number of
smells

7. Smell
• The number of individual sensations
decreases with age and varies with individuals
• The receptor cells are neurons embedded
within the mucous membrane of the nasal
epithelium
• The dendrites of these cells are known as
olfactory hairs, which physically interact with
odorants, and the axons extend into the
olfactory bulb of the brain (Animation)

8. Olfactory Pathway
• Inhaling causes gas molecules to move into
the nasal cavity where they dissolve into
mucous
• Begins with olfactory hairs of receptor cells
interacting with molecules; if an action
potential is generated, it will move up to the
olfactory bulb, located beneath the origin of
the olfactory nerves

10. Olfactory Pathway
• From the olfactory bulb the impulse continues
along to the frontal lobes of the cerebral
cortex for interpretation
• This makes smells linked very powerfully to
memories
• Video: How Many Smells Can We Smell?

11. Taste
• The sense of taste is also known as gustation
• Often works with smell to gain a complete
analysis of the sensation
• Special organs of taste are known as “taste
buds” and approximately 10,000 are located
on the surface of the tongue within small
elevations known as papillae
• Other taste buds may be found on the roof of
the mouth and walls of the pharynx

13. Taste
• Each taste bud has several taste receptors,
known as gustatory cells
• The free ends of gustatory cells have
microvilli, called taste hairs that project
through an opening in the taste bud known as
a taste pore
• At the base of the gustatory cells is a network
of sensory nerve fiber endings (Animation)

15. Taste
• There are five
primary tastes:
sweet, sour, bitter,
salty, and savory (or
umami)
• Combinations of
these sensations
produce distinct
flavors along with
the sense of smell

16. Gustatory Pathway
• If an action potential is produced by a
gustatory cell, the nerve impulse travels up
the cranial nerve to the medulla oblongata
before being directed to the gustatory center
in the cerebral cortex