The inner ear is located inside the auditory capsule or shrutikotar of the crown. Its main part is the membranous labyrinth. It is covered by bony labyrinth. The membranous labyrinth is filled with endolymph and the bony labyrinth with perilymph. The inner ear consists of two chambers. The human balance organ is called the vestibular apparatus. It is composed of utriculus and sacculus.
1. Utriculus: The spherical chamber at the top of the inner ear is called utriculus. It consists of 3 semicircular canals. 2 vertical ducts and 1 horizontal duct. The ducts are located at right angles to each other. One end of each duct swells to form an ampulla.
The ampulla contains the sensory cells or macula. Sensory cells give rise to sensory hair cells. Sensory hair cells are embedded in otolith grains (stones). Otolith granules are covered by cupula. Utriculus maintains body balance.
2. Sacculus: The lower chamber of the inner ear is called sacculus. It forms a patchy tube like a snail shell. It is called cochlea. Cochlea has 3 chambers. scala vestibuli, scala media and scala tympani. The scala vestibuli is superior and filled with perilymph, the scala media is medial and filled with endolymph, and the scala tympani is inferior and filled with perilymph. The scala media consists of Ressner’s membrane above and Basil’s membrane below. Some epithelial cells above the basilar membrane transform to form the organ of Corti. Organ of Corti is a sensory organ. Organ of Corti contains 5000 sensory neurons. The place where the scala vestibula and scala tympani meet is called the helicotrima.