I have been reading about innervations of the olfactory bulb, but I don´t understand this concept well. What exactly does centrifugal innervation mean? Is it some kind of special fiber organization in the bulb? Or is it just a common term? Can anyone help me with this?
They are standard, though uncommon, terms. "Centrifugal" means from this location, heading away. "Centripetal" means from elsewhere, coming here. Or if you like, centrifugal means outgoing, and centripetal means incoming.
Sometimes these terms are modified for specific structures, e.g. corticofugal connections are connections made from the cortex to areas outside the cortex.
Centrifugal (from latin center-fleeing) is a general term for axons leaving "higher" brain centers and targeting "lower" or more peripheral brain centers. It is not the most common term for such pathways, and as you point out it is not the clearest term to use. I prefer "top down" or "feedback" projections, although these contain their own assumptions about what regions of the brain are "on top", which could be argued either way.
In the case of the olfactory bulb, centrifugal fibers would be axons from the olfactory cortex, which project back to targeting cells in the bulb. The term is used to distinguish these fibers from the more standard projections from the sensory nerve endings into the bulb, and from the bulb into the olfactory cortex. This 'standard' input path is the bottom up sensory information flowing into the higher association cortices, while the feedback from those higher regions forms the top-down centrifugal pathway.
For reference: http://www.ncbi.nlm.nih.gov/pubmed/19159349
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