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The Sense of Smell
k.Vishnu prasanna
Vishnuprasanna_kudumula@yahoo.com
Olfactory Mucous Membrane
-Olfactory receptor cells
-Area of 5cm2
in roof of nasal
cavity near the septum
-10 to 20 millio...
Composition of Olfactory epithelium
-Each neuron has a thick
dendrite with an expanded
end called olfactory rod
-From rods...
Mucus producing Glands
-Olfactory mucous
membrane is
constantly
covered by mucus
-Mucus is
produced by
Bowman’s glands,
pl...
Olfactory Bulbs
-Axons of receptors
contact the primary
dendrites of mitral cells
and tufted cells.
-Forming complex globu...
Olfactory Bulbs
-Granule cells
have no axons
and make
reciprocal
synapses with
lateral dendrites
of tufted and
mitral cell...
Stimulation of Olfactory cells
Stimulation of Olfactory cells
G-protein is stimulated
-triggers activation of Adenyl
cyclase (enzyme speeds up the
conver...
Stimulation of olfactory cells
Transmission of smell signals to CNS
Olfactory thresholds and discrimination
Substance mg/L of Air
Ethyl ether 5.83
Chloroform 3.30
Pyridine 0.03
Oil of pepper...
Vomeronasal Organ
Organ is not well developed
in humans very well
developed in rodents
This organ is concerned
with percep...
Role of Pain Fibers in the Nose
Many trigeminal
pain fibers are
found in olfactory
membrane
They are
stimulated by
irritat...
Abnormalities
 Anosmia – absence of
sense of smell
 Hyposmia – diminished
olfactory sensitivity
 Dysosmia – distorted
s...
Summary
Bibliography
 Guyton and Hall, Medical physiology,10th
edition
 Elsevier Ltd. Boron & Boulpaep: Medical
Physiology, upda...
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The sense of smell

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Transcript of "The sense of smell"

  1. 1. The Sense of Smell k.Vishnu prasanna Vishnuprasanna_kudumula@yahoo.com
  2. 2. Olfactory Mucous Membrane -Olfactory receptor cells -Area of 5cm2 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
  3. 3. Composition of Olfactory epithelium -Each neuron has a thick dendrite with an expanded end called olfactory rod -From rods cilia project to the mucous surface -Each receptor neuron has 10- 20 cilia -Axons of olfactory receptor neurons pierce cribriform plate of ethmoid bone and enter olfactory bulbs -Olfactory neurons have half- time of few weeks.
  4. 4. 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
  5. 5. Olfactory Bulbs -Axons of receptors contact the primary dendrites of mitral cells and tufted cells. -Forming complex globular synapses called olfactory glomeruli. -Periglomerular cells are inhibitory neurons connecting one glomerulus to another
  6. 6. Olfactory Bulbs -Granule cells have no axons and make reciprocal synapses with lateral dendrites of tufted and mitral cells -Mitral and Tufted – excite granule releasing glutamate and granule cell in turn inhibits both by releasing GABA
  7. 7. Stimulation of Olfactory cells
  8. 8. Stimulation of Olfactory cells G-protein is stimulated -triggers activation of Adenyl cyclase (enzyme speeds up the conversion of ATP to cAMP – cAMP then binds to action channels in membrane of cilia- this causes channels to open and Ca ions to enter cilia – influx of Ca ions activates Cl channels to open and Cl leaves. Membrane becomes depolarized and AP is created. The action potential travels down the axon of olfactory receptor cell eventually meets with the other axons and forms the olfactory nerve (CN I)
  9. 9. Stimulation of olfactory cells
  10. 10. Transmission of smell signals to CNS
  11. 11. Olfactory thresholds and discrimination Substance mg/L of Air Ethyl ether 5.83 Chloroform 3.30 Pyridine 0.03 Oil of peppermint 0.02 Iodoform 0.02 Butyric acid 0.009 Propyl mercaptan 0.006 Artificial musk 0.00004 Methyl mercaptan 0.0000004 Olfactory receptors respond only to substances in contact with olfactory epithelium and need to be dissolved in mucus Methyl marcaptan one of the substances in garlic can be smelled at very low concentration showing the remarkable sensitivity of olfactory receptors Humans can recognize more than 10.000 different odors However determination of intensity of odor is poor
  12. 12. Vomeronasal Organ Organ is not well developed in humans very well developed in rodents This organ is concerned with perception of odors that act as pheromones There is evidence of pheromones in humans and a close relationship between smell and sexual function
  13. 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. 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
  15. 15. Summary
  16. 16. Bibliography  Guyton and Hall, Medical physiology,10th edition  Elsevier Ltd. Boron & Boulpaep: Medical Physiology, updated edition  William F.Ganong, Review of Medical Physiology, 22nd edition  Ward, Clarke & Linden,Physiology at a glance
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