Histologic Section of the Apex
of the Guinea Pig Cochlea
When seen in conventional histologic sections, it is difficult to gain
an appreciation of the 3D structure of the helicotrema. We have
therefore performed 3D reconstructions of the cochlear fluid spaces
that allow us to see the anatomy in correct 3D detail.
Ears were imaged using a tehnique called OPFOS (Orthogonal-Plane
Fluorescence Optical Sectioning). This consists of chemically making
the intact ear transparent, and then photographing individual sections
(about 8 microns wide, as seen in the left image above) by illuminating
them with a laser.
This allows highly accurate 3D images that would not be possible if you
sectioned the ear histologically. Each fluid space bounday is then
traced in all 3 dimensions, allowing the entire 3D structure to be
reconstructed as shown at the right.
This image is made from a 3D reconstruction by cutting away the outer
wall of the cochlea at the apex.
It gives a good view of what is "inside", but it can still be difficult
to make out 3D structures from 2D pictures.
To understand the 3D relationships better, movies are much better, as
shown below.
The colors in this image are as follows: Dark Blue indicates the
endolymphatic space. As we are looking into the cochlea through the
scala vestibuli (with the outer wall cut away) the blue structure you
see represents Reissner's membrane. Cyan represents the organ of Corti,
the sensory structures of the ear. Gray represents bone. Yellow
represents the spiral ligament.
MP4/OLV Video of Helicotrema Reconstruction
In the video, you can see that we are looking into a chamber, which
is the apical part of scala vestibuli.
The tube entering this apical chamber at the middle, is the scala
tympani, which is turned almost 90 degrees, compared with its
orientation further down the cochlea. The bony "floor" of scala tympani
makes a thin bony septum (gray) while the sensory structures (cyan) and
Reissner's membrane (blue) run almost vertically.
There is no "narrowing" of the scala at the helicotrema, as some text
books suggest. Instead, scala tympani just opens into the apical
chamber.
If you are running Internet Explorer then you can
download the video file by clicking here
