INTERNAL EAR -

• It is called membranous labyrinth protected by bonny labyrinth of periotic bone (Frontal, Temporal and Parietal).
• Between internal ear and bonny labyrinth perilymph is present.
• Internal ear consists of vestibule (utriculus and sacculus), semi circular canals and cochlear duct.

• Utriculus is oblong sac, sacculas is globular sac.
• Both one connected by sacculo-utricular duct from which endolymphatic duct is originated, form endolymphatic sac.
• In utriculus 3 semi circular canals open, placed at 90o to each other, these are superior posterior and lateral.
• Superior and posterior are vertical joined by cruss commune. Lateral is horizontal both ends of each duct are enlarged to form ampulla
• Ampullae of superior and lateral ducts lie closely. Each ampullae has sensory spot cristae for equilibrium.
• In utriculus and sacculus 2 acaustic spot macula present.

                      T.S. OF CRISTAE OF RABBIT                                                     T.S. OF CRISTAE OF MAN

• A macula/ criste consists of sensory cells and supporting cells. Supporting cells are columner.
• Sensory cells bear small stereocillia and one large kinocillium.
• Tips of cillia project into a thick gelatinous, glycoprotein sheet i.e. otolithic membrane.
• It conists of otolith or otokonia or statolith, made up of protein & calcium.
• Cristae resembles a maculae in structure except that it lies on an elevation i.e. acoustic ridge, sensory cells have longer hair and its gelitinous mass is dom shaped lacks otoliths and is called capula.
• From sacculus chochlear duct or lagena is originated surrounded by chochlear and bonny labyrinth.
• It is 35 mm long, spirally coiled, having coiling in whale , in rabbit  around central spongy bone mass

i.e. modiolus

T.S. OF CHOCHLEA

• Cochlear duct is lined by cuboidal epithelium.
• Between sacculus and chochlear duct, ductus reunience present that analyse the pitch of sound.
• Lumen of chochlea is devided into scala vestibuli, scala media, & scala tymbani by reisner's membrane and basilaris membrane.
• Scala vestibuli is connected to fenestra ovalis. Scala tympani is connected to fenestra rotundus.
• Scala vestibuli & scala tympani at distal end are connected to each other by helicotrema.
• In scala vestibuli & scala tympani perilymph is present. (Sodium rich and potassium poor).
• Is scala media endolymph (Sodium poor, Potassium rich) present.
• Endolymph is secreated by straita vescularis of scala media.
• By the out growth of basilaris membrane organ of corti are formed having 24,000 receptor cells.

Organ of corti

• Organ of corti is protected by tectorial membrane. In organ of corti pillar cells, henson's cells and dietor cells are present.From its lower part auditory nerve is originated. At free end of henson's cells stereocillia are present.