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”
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
5.
6.
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
9.
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
12.
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)
14.
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
