Sense of smell


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Sense of smell

  2. 2. Smell
  3. 3. Chemical Senses: Taste and Smell  Both senses use chemoreceptors  Stimulated by chemicals  Taste has four types of receptors  Smell can differentiate a large range of chemicals  Both senses complement each other and respond to many of the same stimuli  Olfaction (smell) and gustation (taste)  Both project to cerebral cortex & limbic system  Evokes strong emotional reactions
  4. 4. Olfactory organs •Contain olfactory receptors and supporting epithelial cells •Cover parts of nasal cavity and a portion of the nasal septum Olfactory receptors •Chemoreceptors •Respond to chemicals dissolved in liquids Olfactory Epithelium •Located on roof of nasal cavity •Contain olfactory receptor cells with columnar supporting cells •Covered by mucous to trap airborne molecules Sense of Smell
  5. 5. Olfactory Epithelium
  6. 6. 6 Cells of the Olfactory Membrane  Olfactory receptors  bipolar neurons with cilia or olfactory hairs  Supporting cells  columnar epithelium  Basal cells = stem cells  replace receptors monthly  Olfactory glands  produce mucus
  7. 7. Sense of Smell  Air entering the nasal cavity must make a hairpin turn to stimulate the olfactory receptors before entering the respiratory passageway below  Sniffing  also brings the air superiorly across the olfactory epithelium  intensifies the smell
  8. 8. Olfactory tract Olfactory bulb (a) Nasal conchae Route of inhaled air Olfactory epithelium
  9. 9. Mitral cell (output cell) Olfactory gland Olfactory tract Olfactory epithelium Filaments of olfactory nerve Cribriform plate of ethmoid bone Lamina propria connective tissue Basal cell Supporting cell Dendrite Olfactory cilia Olfactory bulb Glomeruli Axon Olfactory receptorcell Mucus Route of inhaled air containing odormolecules(b)
  10. 10. Olfactory Cells  Dendrites of each olfactory cell  called olfactory cilia  extend into the nasal cavity  Olfactory axons  project upward through the foramina in the cribriform plate of the ethmoid bone of the skull  synapse on neurons within the olfactory nerve
  11. 11. Physiology of Smell  Series of events  the chemical must be volatile  it must be in the gaseous state as it enters the nasal cavity  the chemical must be water soluble  so that it can dissolve in the fluid containing the olfactory epithelium  the dissolved chemicals stimulate the olfactory receptors by binding to protein receptors in olfactory cilium membranes  the generation of APs in the olfactory cells  an impulse travels through the olfactory cell axons to the olfactory nerve where the smell sensation is transmitted to the brain
  12. 12. OLFACTORY PATHWAY  As air enters the nasal passageway the level of odor- producing chemicals dissolve in the mucus membrane  With in the mucus membrane the olfactory cilia capture the chemicals  After reaching a threshold level it is passed to the olfactory nerves located in the olfactory bulb  The impulse passes through the olfactory tract and into the thalamic and olfactory centers of the brain for interpretation, integration, and memory storage.  The sense of smell can create powerful and long-lasting memories. That often persist from early childhood to death
  13. 13. Olfactory Nerve Pathways  Olfactory receptor fibers synapse with neurons in the olfactory bulbs (cranial nerve I).  Impulses travel along the olfactory tracts  Impulses are interpreted in olfactory cortex.  Olfactory receptor neurons are in direct contact with the environment and can be replaced if damaged.  Olfactory receptors undergo sensory adaptation rapidly  Sense of smell drops by 50% within a second after stimulation
  14. 14. Transmission of smell signals to CNS
  15. 15. 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
  16. 16. Anosmia Absence of the sense of smell  Trauma  Colds or allergies producing excessive mucus  Polyps causing blockage  1/3 are from zinc deficiency