2014 Sensory Physiology

Olfactory pathways & pattern coding

  • individual primary afferent neurons express a single type of receptor

  • each neuron that expresses a particular receptor type projects to a specific glomerulus within the main olfactory bulb (MOB), establishing an organizational map at the level of the second order neurons
    • i.e., dark and light green ORNs are scattered randomly throughout the main olfactory epithelium, but their axons segregate into different glomeruli

  • this indicates that olfactory information processing has some characteristics of labelled line theory
Projections of olfactory epithelium
Olfactory receptor codes
  • this segregation sets up a mechanism whereby odourants can be coded by the pattern of activity in the olfactory bulb

  • odourants can be coded based on the combination of receptors that respond (14 are shown here)

  • Richard Axel and Linda Buck won the 2004 Nobel prize in Medicine for unraveling the coding scheme for odourants

Odourtopic maps

  • systematic mapping of the responses to >300 odourants (reviewed in Johnson and Leon, 2007) confirms the spatial organization of the olfactory bulb: an odourtopic map that has a similar organization to the stimulus-specific maps found in other sensory systems

  • these studies have also shown that lateral inhibition narrows the range of chemicals that indivdual olfactory bulb neurons respond to


Email: Dr. Janet Fitzakerley | ©2014 University of Minnesota Medical School Duluth | Last modified: 4-feb-14 8:26 PM