Re: Efferent feedback to the organ of the Corti

["Keith N. Darrow" <kdarrow@xxxxxxx>]

Dear Everyone,

I am relatively new to this 'set' of e-mails and I send this response under the
assumption that the topics are open to public discussion.

I am somewhat confused as to WHICH olivocochlear efferent system we are
speaking of. I assumed from the the first e-mail by Matt Flax that we were
discussing the LOC and IHC area innervation, whereas the second e-mail from
David Smith appears to be referring to the MOC and OHC innervations patterns.

Guinan et al., (1984) comprehensive work demonstrates the innervation patterns
of the olivocochlear systems in cat. In figure 4 a summary of their work shows
that the LOC system innervates almost unfiormly the ipsilateral IHC region
(with some possible emphasis on the more basal portion). In contrast, the
(assumed) MOC fibers send 2/3 innervation to the contralateral cochlea - in
which there is a definate trend that the MOC fibers are more heavily
concentrated in the basal portion (10 - 30 Khz) of the OHCs, with signifigant
roll off more apicaly and most basaly.

In final, I also think it is wrong to assume that more innervation = more
effect. The neurotransmitters used, their function, and the effectiveness of
their respsective receptors would be most liekly to determeine a fibers
overall "effect".


Keith N. Darrow

Reference: Guinan, Warr, and Norris. (1984) Topographic Organization of the
Olivocochlear Projections from the Lateral and Medial Zones of the Superior
Olivary Complex. Journal of Comparative Neurology.




Quoting Matt Flax <flatmax@IEEE.ORG>:

> David, please forgive me if I am incorrect.
>
> I am referring to [1] Figure 5 where the VR/NP Synapses on VP/NR
> NFs (Presumed Axodendritic Synapses) are depicted to become less numerous
> towards the 3'rd turn.
>
> Again, I am an electrical engineer, so please forgive me if I am
> mistaken, but I am assuming that these are efferent neural connections.
>
> I also refer to this posting to Auditory in 1996 :
> http://www.auditory.org/postings/1996/74.html
> Where it is stated ...
> "There are also efferent fibers near the IHC's. These originate in the
> lateral olivocochlear system, and make axodendritic synapses with the
> afferent fibers [3]".
>
> Matt
>
> [3] Nadol J.B., Jr., Synaptic morphology of inner and outer hair cells of
> the human organ of Corti, Journal of electron microscopy technique, 15,
> 187-196, 1990.
> [1] @article{Thiers:2002,
> author    = {Thiers, F.A. and Burgess, B.J. and Nadol, J.B.},
> title     ={\href{http://www.elsevier.com/locate/issn/03785955}{Axodendritic
> and
> dendrodendritic synapses within outer spiral bundles in a human}},
> journal   = {Hearing Research},
> pages     = {97-104},
> year      = {2002},
> volume    = {164},
> issue     = {1-2}
> }
>
> On Thu, Oct 10, 2002 at 06:48:53AM -0400, David W. Smith, Ph.D. wrote:
> > Matt,
> > I think if you review Sato et al. (The innervation of outer hair cells:
> > 3D reconstruction from TEM  serial sections in the Japanese macaque),
> > Hearing res. 135,  29-38, 1999, you will see this is not precisely true.
> > In  fact, the apex has a very robust, and perhaps qualitativiely
> > different medial efferent supply than do more basal regions.  Your
> > statement "In fact the afferent system is reported to be oversampled by
> > the efferent system at high frequencies, one to one sampled for medium
> > frequencies and under-sampled for low frequencies,"  I believe is
> incorrect.
> > David SMith.
> >
> > Matt Flax wrote:
> >
> > >I would like to point researchers to the article [1] which slivers the
> > >cochlea for electron microscope inspection. Of interest is the finding
> > >that the efferent neural innervation is mostly in contact with the high
> > >frequency portion of the spiral ganglion / organ of the Corti. There is
> > >completely minimal contact for the low frequency portion of the  spiral
> > >ganglion / organ of the Corti. There is medium contact for medium
> > >frequencies.
> > >In fact the afferent system is reported to be oversampled by
> > >the efferent system at high frequencies, one to one sampled for medium
> > >frequencies and under-sampled for low frequencies.
> > >
> > >This suggests that low frequencies are uniquely unaffected by the
> > >efferent system. Medium frequencies are affected by efferent feedback and
> > >high frequencies are seriously under the influence of the efferent
> > >system.
> > >
> > >It is also noted that the efferent system is believed to develop post
> > >birth.
> > >
> > >Matt
> > >
> > >[1]
> > >@article{Thiers:2002,
> > >  author    = {Thiers, F.A. and Burgess, B.J. and Nadol, J.B.},
> > >  title     =
> > >{\href{http://www.elsevier.com/locate/issn/03785955}{Axodendritic and
> > >dendrodendritic synapses within outer spiral bundles in a human}},
> > >  journal   = {Hearing Research},
> > >  pages     = {97-104},
> > >  year      = {2002},
> > >  volume    = {164},
> > >  issue     = {1-2}
> > >}
> > >
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> > >
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> > >
> >
>
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