The labyrinth lies in the otic capsule in the petrous temporal bone. The otic capsule consists of three chambers:
The cochlea anteriorly. This is constituted by a spiral of two and a half turns. The posterior vestibular apparatus, consisting of saccule, utricle and semicircular canals or ducts. These vestibular end organs respond to hair cell movement.
The posterior vestibular chamber. The semicircular canals communicate with this chamber through five round openings. These chambers of the membranous labyrinth are surrounded by perilymph and are suspended by fine connective tissue strands from the bony labyrinth. Perilymph is continuous with cerebrospinal fluid in the subarachnoid space. The membranous labyrinth contains endolymph. This is formed by the secretory cells of the stria vascularis of the cochlea. It has a high potassium content (145 mmol/l) and a low sodium content (5 mmol/l).
The perilymph has a composition similar to the extracellular fluid and the cerebrospinal fluid. The endolymph resembles intracellular fluid. The two labyrinthine fluids do not mix.
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