Cochlear aqueduct

THE INTERNAL EAR The internal ear or the labyrinth is an impoant organ of hearing and balance. It consists of a bony and a membranous labyrinth. The membranous labyrinth is filled with a clear fluid called endolymph while the space between membranous and bony labyrinths is filled with perilymph. BONY LABYRINTH It consists of three pas: the vestibule, the semicircular canals and the cochlea. Cochlea: The bony cochlea is a coiled tube making 2.5 to 2.75 turns round a central pyramid of bone called modiolus. The base of modiolus is directed towards internal acoustic meatus and transmits vessels and nerves to the cochlea. Around the modiolus and winding spirally like the thread of a screw, is a thin plate of bone called osseous spiral lamina. It divides the bony cochlea incompletely and gives attachment to the basilar membrane. The bony bulge in the medial wall of middle ear, the promontory, is due to the basal coil of the cochlea. The bony cochlea contains three compaments: (a) Scala vestibuli, (b) Scala tympani, (c) Scala media or the membranous cochlea. The scala vestibuli and scala tympani are filled with peri- lymph and communicate with each other at the apex of cochlea through an opening called helicotrema. Scala vestibuli is closed by the footplate of stapes which separates it from the air-filled middle ear. The scala tympani is closed by secondary tympanic membrane; it is also connected with the subarachnoid space through the aqueduct of cochlea. Ref:- Dhingra; pg num:-09,10