1. Sense of Smell

2. Olfactory Organs lie in nasal epithelium mucous membrane
total area of olfactory epithelium is less than 1 square inch
located in superior portion of nasal cavity
- superior nasal conchae
- part of nasal septum

3. Olfactory Epithelium Consists of three types of cells:
- olfactory receptors
- supporting cells
- basal cells

4. Olfactory Receptors
million
lifespan about 30 days

5. Olfactory Receptors (cont.)
bipolar neurons with knob-shaped dendrite at distal end
- cilia called olfactory hairs protrude from dendrite
- cilia are sites of olfactory transduction
respond to chemical stimulation of an odorant molecule
single axon projects into olfactory bulb at proximal end

6. Supporting Cells
columnar epithelial cells of mucous membrane lining the nose
surround and support olfactory receptors

7. Basal Cells located around supporting cells
stem cells that produce new olfactory receptors (neurons)

8. Olfactory Glands also called Bowman’s glands
within connective tissue that supports epithelium
produce mucus
- moistens surface of olfactory epithelium
- dissolves odorant gasses
- continued production clears surface area and prevents continued stimulation by same odor

9. Physiology of the Sense of Smell

10. Olfactory Stimulation
Primary scents:
- floral
- pungent
- musky
- minty
- putrid
- camphoraceous
- etheral

11. Olfactory Stimulation (cont.)
irritating odors also stimulate lacrimal and nasal receptors producing tears and sniffles
Example:
- onions

12. Olfaction or Transduction
chemical interaction with receptor sites
- sodium channels open leading to depolarization which causes action potential in axon leading to olfactory bulb
low threshhold - only a few molecules of a substance in the air are necessary to stimulate olfactory receptors

13. Adaptation decreasing sensitivity to odors
occurs rapidly; about 50% in the first second after stimulation and very slowly thereafter
even though adaptation to one odor has occurred, sensitivity to other odors remains unchanged

14. Olfactory Pathway olfactory receptors olfactory nerves olfactory bulbs
olfactory tract
prepyriform cortex and limbic system
frontal lobes