The document discusses the key structures involved in the sense of smell, including the olfactory mucous membrane, olfactory receptor cells, and olfactory bulb. It describes how odorant molecules are transmitted from the air to receptor sites on olfactory receptor cell cilia through mucus and odorant binding proteins. Signals from the olfactory receptor cells are then transmitted to the olfactory bulbs and other areas of the central nervous system to be processed as the sense of smell. Dysfunctions of the olfactory system can result in abnormalities such as anosmia, hyposmia, and dysosmia.

2. The Sense of Smell
Gonçalo Martins

3. Structures
 Olfactory Mucous Membrane
 Olfactory Receptor Cells
 Olfactory bulb

4. Basics: What do you need for
smell?
• Odorous Substance
• Airborne
• Perceptual system that can parse or segregate
the information in airborne odorant molecules

5. Olfactory Mucous Membrane
-Olfactory receptor cells
-Area of 5cm in roof of nasal
cavity near the septum
-10 to 20 million receptor
cells
-Each olfactory receptor is a
neuron
-Olfactory mucous
membrane is the place in
body where NS is closest to
external world

6. Olfactory Receptor Cells

7. Physiology contd.
Olfactory Receptor Cells have cilia
Cilia are bathed in mucous
Mucous contains Odorant binding
proteins (OBP)
OBP transmits the odorant molecules
from the air to receptor sites on the
cilia

8. Mucus producing Glands
-Olfactory mucous
membrane is
constantly
covered by mucus
-Mucus is
produced by
Bowman’s glands,
placed just under
the basal lamina
of the menbrane

9. Olfactory Bulbs

10. Physiology
Nasal Cycle
• Olfactory Epithelium
• Olfactory Receptor Cells
(Complete Neurons)
• Free Nerve Endings
• Olfactory Nerve
(Axons of the ORCs)

11. Olfactory Pathways

12. Transmission of smell signals to CNS

13. Role of Pain Fibers in the Nose
Many trigeminal
pain fibers are
found in olfactory
membrane
They are
stimulated by
irritating
substances
Are responsible
for initiating
sneezing,
lacrimation and
other reflex
responses.

14. Abnormalities
 Anosmia – absence of
sense of smell
 Hyposmia – diminished
olfactory sensitivity
 Dysosmia – distorted
sense of smell
 More than 75% of
humans over the age
of 80 have an impaired
ability to identify smells