EXERCISE 13

ENDOSCOPIC DISSECTION OF SECOND TURN OF COCHLEA

The length of 2nd turn of cochlea is 8 to 8.5 mm and the diameter is 1.5 mm.
The second turn is situatad infront of the basal turn .
The anterior wall of the basal turn and the posterior wall of the second turn forms bony partition between two spiral cavities.
The second spiral turn is smaller than the first, partially dovitails into first.

STEP A – The second spiral tuns spirals around the modiolus .
The scala vestibuli is bigger than scala tympani (reverse in basal turn).
The width of basilar membrane is medium in this turn, hence it is the resonant site for middle frequencies At +01 the apex of the middle turn the modiolus ends. we can see plenty of nerve endings so many times

STEP B – HABENCULA PERFORATA…. These are plenty of orifices present on the surface of the osseus spiral lamina and carries nerve endings (black spots) .
We can observe the SPIRAL CANAL OF ROSENTHAL at the periphery of the modiolus.
It is 0.1 to 0.2 mm in diameter its origin correseponds to the origin of the osseus spiral lamina.
There is a bony projection where the basilar membrane to the periphery bony capsule that is secondary bony spiral lamina.

STEP C – SCALA TYMPANI AND SCALA VESTIBULI OF SECOND TURN
In second turn scala vestibuli is bigger than scala tympani.
They are clearly visualised with Basilar membrane.

STEP D – SCALA MEDIA OF SECOND TURN
The scala media is seen with Reissners membrane, the basilar membrane and stria.

1 – Modiolus
2 – Rosenthal canal
3 – Hebencula perforata with nerve endings (black spots).
4 / OSL – Osseus spiral lamina
5 / BM – Basilar membrane
6 – Secondary spiral lip
SV – Scala vestibuli
ST – Scala tympani
EMO – End of modiolus
SM – Scala media
BM – Basilar membrane
RM – Reissners membrane
S – Stria vascularis