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

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

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

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