Internal ear

an intricate set of interconnected spaces the bony labyrinth, houses a set of continuous fluid-filled, epithelium-lined tubes chambers that make up the smaller membranous labyrinth

The bony labyrinth has an irregular central cavity, the vestibule, where the saccule and the utricle are located. Behind this, three osseous semicircular canals enclose the semicircular ducts. On the other side of the vestibule, the cochlea (L. cochlea, snail, screw) contains the cochlear duct

Major divisions of the membranous labyrinth 1. the vestibular labyrinth, which mediates the sense of equilibrium Consists of two connected sacs (the utricle and the saccule) three semicircular ducts arising from the utricle, and

2. the cochlear labyrinth, which provides for hearing and contains the cochlear duct connected to the saccule.

In each of these structures large areas of columnar sensory mechanoreceptors called hair cells are present in specialized regions 2 maculae in utricle and saccule 3 cristae ampullaries in ampullae of semicircular canals The long spiral organ of Corti in cochlear duct

The bony labyrinth has an irregular central cavity, the vestibule, where the saccule and the utricle are located. Behind this, three osseous semicircular canals enclose the semicircular ducts. On the other side of the vestibule, the cochlea (L. cochlea, snail, screw) contains the cochlear duct

The cochlea is about 35 mm in length and makes two-and-one-half turns around a bony core called the modiolus. The modiolus contains blood vessels and surrounds the cell bodies and processes of the acoustic branch of the eighth cranial nerve in the large spiral or cochlear ganglion.

All regions of the bony labyrinth are filled with perilymph, which is similar in ionic composition to cerebrospinal fluid and the extracellular fluid of other tissues, but contains little protein. Perilymph emerges from the microvasculature of the periosteum and is drained by a perilymphatic duct into the adjoining subarachnoid space.

This fluid suspends and supports the closed membranous labyrinth, protecting it from the hard wall of the bony labyrinth. The membranous labyrinth is filled with endolymph, which also contains few proteins and is further characterized by a high potassium (150 mM) and low sodium (16 mM) content, similar to that of intracellular fluid.

Endolymph is generated largely by capillaries in the stria vascularis in the wall of the cochlear duct and is drained from the vestibule into venous sinuses of the dura mater by the small endolymphatic duct

Details of cochlea

Structure of organ of Corti

Details of saccule,utricle

Otoliths

Cristae ampullaris