Olfaction

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Olfaction

  1. 1. 1PHYSIOLOGY OF OLFACTION
  2. 2. 2PHYSIOLOGY OF OLFACTION
  3. 3. 3PHYSIOLOGY OF OLFACTION
  4. 4. 4PHYSIOLOGY OF OLFACTION
  5. 5. 5PHYSIOLOGY OF OLFACTION FOOD GAS LEAKS FIRE
  6. 6. 6PHYSIOLOGY OF OLFACTION
  7. 7. It contains 50 million bipolar olfactory sensory neurons mixed with supporting(sustentacular)cells,basal stem cells It is the place where nervous system is closest to the external world. New sensory neurons are generated by Basal stem cells. Epithelium is covered by mucus secreted by Bowman glands and supporting cells . 7PHYSIOLOGY OF OLFACTION
  8. 8. Each sensory neuron terminates in to a knob which contain CILIA. Cilia are unmyelinated processes that protrude in to mucus. Odorant molecules dissolve in the mucus and bind to receptors. Mucus provides appropriatr molecular and ionic environment for odour detection. 8PHYSIOLOGY OF OLFACTION
  9. 9. The axons pass through cribriform plate and enter the olfactory bulb. Mitral cells , tufted cells ,meet the axons in bulb to form glomeruli. 9PHYSIOLOGY OF OLFACTION
  10. 10. Periglomerular cells-inhibitory neurons which connect glomeruli . Granule cells-no axons ,reciprocal connections with mitral and tufted cells. Mitral and tufted cells secrete glutamate and granule cells secrete GABA. Epithelium also contains the trigeminal pain fibers . 10PHYSIOLOGY OF OLFACTION
  11. 11. OLFACTORY CORTEX The axons of the mitral and tufted cells pass through lateral olfactory stria to terminate on the dentrides of the olfactory cortex . Olfactory cortex contains :- anterior olfactory nucleas ,olfactory tubercle, piriform cortex , amygdala ,entorhinal cortex. 11PHYSIOLOGY OF OLFACTION
  12. 12. From olfactory cortex it goes the orbitofrontal complex which is generally greater on right side thus the representation of olfaction is asymmetric. 12PHYSIOLOGY OF OLFACTION
  13. 13. VOMERONASAL ORGAN PHERMONES REPRODUCTIVE AND INGESTIVE BEHAVIOUR Ex:-pregnancy block in rat 13PHYSIOLOGY OF OLFACTION
  14. 14. There is evidence for existence of phermones in humans and there is a close relationship between smell and sexual function. Sense of smell is more acute in females more at the time of ovulation. 14PHYSIOLOGY OF OLFACTION
  15. 15. HOW IT CAN DISCRIMINATE 10000 DIFFERENT ODOURS? 15PHYSIOLOGY OF OLFACTION
  16. 16. There are approxiamately 500 olfactory genes which constitute 2%of human genome The amino acid sequences of receptors is very diverse ,but all are G- protein coupled receptors. The GPCR contains three sub units α,β,gamma. When a chemical attaches these dissociate and α activates adenylate cyclase to catalyze the production of cAMP . 16PHYSIOLOGY OF OLFACTION
  17. 17. The result is inward directed calcium current which produces graded receptor potential. This opens the calcium activated chloride channels further depolarising the cell due to high intra cellular chloride levels. If the stimulus is sufficient for the receptor potential to exceed its threshold,an action potential is triggered. Each neuron projects to one/two glomeruli. Lateral inhibition – sharpens the olfactory signals 17PHYSIOLOGY OF OLFACTION
  18. 18. ODOR DETECTION THRESHOLD ODORANT BINDING PROTEINS ADAPTATION Long term adaptation:cGMP Short term adaptation:cAMP 18PHYSIOLOGY OF OLFACTION
  19. 19. ANOSMIA HYPEROSMIA DYSOSMIA TREATMENT:-Antibiotics,surgery,steroids. 19PHYSIOLOGY OF OLFACTION
  20. 20. 20PHYSIOLOGY OF OLFACTION

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