2014 Sensory Physiology

Olfactory epithelia

  • the primary olfactory epithelium is located at the top of the nasal cavity
  • odourants are dissolved in the mucus layer and are bound to olfactory binding proteins that chaperone the passage of the odourants to the cilia-like projections of the olfactory receptor neurons (ORNs)

  • unlike other special sense receptors, the olfactory receptor membrane is found on the primary afferent neurons (i.e., receptor=primary afferent)

  • olfactory receptor cells are the only neurons that are regularly replaced throughout life (via differentiation of supporting basal cells)

  • ORN axons enter the CNS through the cribriform plate to synapse in the olfactory bulb
    • there are many olfactory "nerves" consisting of collections of ORN axons

  • the olfactory pathway is the only sensory pathway that does not relay in the thalamus
    • axons from mitral cells in the olfactory bulb form the olfactory tract
    • these axons synapse in various cortical regions (anterior olfactory nucleus, piriform cortex, the medial amygdala and entorhinal cortex)
    • these direct connections to the limbic system explain why odours are usually the most powerful sensory stimuli for evoking memories
Nasal cavity
Olfactory receptor cells
Email: Dr. Janet Fitzakerley | ©2014 University of Minnesota Medical School Duluth | Last modified: 4-feb-14 8:26 PM