Osseous and Membranous Cochlea

Bony labyrinth is filled with what fluid

perilymph

Membranous labyrinth is filled with what fluid

endolymph

Parts of the bony labyrinth

Vestibule, cochlea, SSC

This houses the membranous labyrinth

Bony labyrinth

Cone shaped spiral with around 2.5-2.75 turns

cochlea

Is cochlea wider at base or the apex

wider at base, narrower at apex

Length of cochlea

35mm long

The bony core of the cochlea

Modiolus

Contains the auditory nerve and blood vessels that supply the cochlea

Modiolus

Bony shelf like structure that winds around the modiolus

Osseous spiral lamina 

Basilar membrane is attached to this

Osseous spiral lamina 

scala media

area between scala vestibuli and scala tympani

filled with endolymph 

Three ducts/chambers within the cochlea

Scala vestibuli

Scala media

Scala tympani

Where the scala vestibuli and scala tympani communicate

Helicotrema

Reissner’s membrane (vestib membrane)

Attaches to the spiral limbus and spital ligament

Spiral ligament

composed of connected tissue cells

Stria vascularis

Manufactures endolymph

source of endolymphatic resting potential 

Cochlear fluids

Perilymph

Endolymph

Cortilymph

Perilymph

Low K+, high Na+

Same chemical composition as CSF

Near 0 mV

found in scala vestibuli and scala tympani

Endolymph

High K+, low Na+

Positive ionic voltage (+80mV)

Found in scala media

Cortilymph

Similar to perilymph; low K+, high Na+

Found in the organ of Corti