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Physiology Lecture 42b: OLFACTION

Physiology Lecture 42b: OLFACTION. Tanveer Raza MD MS MBBS razajju2@yahoo.com. Anatomy. Olfactory mucous membrane Yellowish pigmented specialized olfactory mucous membrane is located in In humans, 5cm 2 in the roof of the nasal cavity near the septum

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Physiology Lecture 42b: OLFACTION

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  1. Physiology Lecture 42b:OLFACTION Tanveer Raza MD MS MBBS razajju2@yahoo.com

  2. Anatomy • Olfactory mucous membrane • Yellowish pigmented specialized olfactory mucous membrane is located in In humans, 5cm2 in the roof of the nasal cavity near the septum • In animals with higher smell sense (dogs) area is larger Tanveer Raza MD MS MBBS razajju2@yahoo.com

  3. Anatomy • Olfactory mucous membrane • Contains • Supporting cells • Progenitor cells • Receptor cells Tanveer Raza MD MS MBBS razajju2@yahoo.com

  4. Anatomy • Olfactory mucous membrane • Contains • Supporting cells • Progenitor cells • Receptor cells • Neurons • Short thick dendrite with expanded end (olfactory rod) Cilia project from here to the surface of mucosa • Axons pierce the cribriform plate of ethmoid bone and enter olfactory bulb • CNS is closest to the external world • Constantly being replaced Tanveer Raza MD MS MBBS razajju2@yahoo.com

  5. Anatomy • Olfactory Bulb • Olfactory glomeruli • Mitral cells • Tufted Cells • Periglomerular cells • Granule cells Tanveer Raza MD MS MBBS razajju2@yahoo.com

  6. Anatomy • Olfactory Bulb • Olfactory glomeruli • Mitral cells • Tufted Cells Axons of olfactory receptor neurons synapse with mitral and tufted cells forming the olfactory glomeruli Mitral and tufted cells send axons to olfactory cortex • Periglomerular cells • Granule cells Tanveer Raza MD MS MBBS razajju2@yahoo.com

  7. Anatomy • Olfactory cortex • Olfactory tract divides to 2 pathways, going into 2 areas • Medial Olfactory Area • Very old Olfactory system • Medial to brain stem • Lateral Olfactory Area • Less Old Olfactory System • Newer System Tanveer Raza MD MS MBBS razajju2@yahoo.com

  8. Smell • Smell pathway has no relay in the thalamus • Poorly developed in humans Tanveer Raza MD MS MBBS razajju2@yahoo.com

  9. Smell Olfactory receptor neurons olfactory mucous membrane Axons pass cribriform plate of ethmoid bone to olfactory bulb Axons synapse with mitral & tufted cells forming olfactory glomeruli Axons of mitral & tufted cells pass through olfactory stria Terminate on apical dendrites of pyramidal cells in olfactory cortex Tanveer Raza MD MS MBBS razajju2@yahoo.com

  10. Olfactory threshold • Remarkable threshold to some substances • Can detect at very low concentration • Methylmercaptan can be smelled when only one 25 trillionth of a gram is present in 1 ml or air • Mixed with natural gas to detect small leaks • Remarkable discrimination • Can recognize over 10,000 different odors Tanveer Raza MD MS MBBS razajju2@yahoo.com

  11. Olfactory discrimination • Poor determination in intensity differentiation • Concentration must be changed 30% [visual is 1% in light intensity] • Smell is more concerned with detecting presence rather that quantitative detection Tanveer Raza MD MS MBBS razajju2@yahoo.com

  12. Odor producing molecules Dissolves in mucus covering olfactory epithelium Comes in contact with olfactory epithelium Produces response Tanveer Raza MD MS MBBS razajju2@yahoo.com

  13. 10,000 different odors, how? • 1000 different odor receptors • Neural organization of olfactory pathway Tanveer Raza MD MS MBBS razajju2@yahoo.com

  14. Odorant Binding Protein (OBP) • OBP concentrates odorants and tranfers them to receptors • Lipophilic odor producing molecules must traverse hydrophilic mucus in nose to reach receptors Tanveer Raza MD MS MBBS razajju2@yahoo.com

  15. Vomeronasal organ • Not well developed in humans • In nasal septum in a pit on anterior third of septum • Perception of odors that act as pheromones • Receptors project to accessory olfactory bulb then to areas in amygdala and hypothalamus concerned with reproduction and ingestive behavior (rodents and other mammals) Tanveer Raza MD MS MBBS razajju2@yahoo.com

  16. Smell and sexual? • Perfume • More acute in Women • More during ovulation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  17. Smell and Food • More important than taste in food selection • Previous bad experience may elicit nausea by the smell of that food Tanveer Raza MD MS MBBS razajju2@yahoo.com

  18. Sniffing • Olfactory area poorly ventilated • Sniffing increase ventilation • Semi-reflex response. New odor attracts attention Tanveer Raza MD MS MBBS razajju2@yahoo.com

  19. Pain fibers in Nose • Trigeminal pain fibers in olfactory mucus membrane • Stimulated by irritating substance • Peppermint • Menthol • Chlorine • Initiates • Sneezing • Lacrimation • Respiratory inhibition • And other reflexes Tanveer Raza MD MS MBBS razajju2@yahoo.com

  20. Adaptation • Rapid • Odor perception decreases and eventually ceases • Due to • Receptor adaptation • Psychological adaptation Tanveer Raza MD MS MBBS razajju2@yahoo.com

  21. Abnormalities • Anosmia • Absence of sense of smell • Hyposmia • Diminished sensitivity • Dysosmia • Distorted Tanveer Raza MD MS MBBS razajju2@yahoo.com

  22. Kallmann’s Syndrome • Hyposmia or Anosmia + Hypogonadism • Low level of circulating gonadotropin • Embryologically, GnRH neurons develop in the nose and migrate up the olfactory nerves and then through the brain to the hypothalamus Tanveer Raza MD MS MBBS razajju2@yahoo.com

  23. Kallmann’s Syndrome “Little” Jimmy Scott Tanveer Raza MD MS MBBS razajju2@yahoo.com

  24. Thank You

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