Sound waves from the external environment are received by the pinna. The received sound waves pass through the auditory meatus and strike the tympanic membrane. It vibrates the tympanic membrane. These vibrations reach the fenestra ovalis through the malleus, incus and stapes. From the fenestra ovalis passes into the perilymph. In the perilymph, the power of sound waves is increased about 20 times. It stimulates the sensory fibers of the organ of corti and generates nerve impulses. These nerve impulses reach the hearing center of the brain through the auditory nerve and the person hears sound.
At the root of the semicircular duct of the inner ear is the ampulla. Inside the ampulla are endolymph and sensory hair cells. A jelly-like cupula is attached to the follicles. The endolymph and cupula are positioned in the direction in which the human head turns or bends. Sensory cells send this message to the brain. Again, utriculus and saccule have organ called saculae. The saccule carries sensory rhombic cells. When the head tilts to one side, the otolith grains exert pressure on the hair follicles. The hair cells are stimulated and the sensation reaches the brain through the nerves. Then man can understand his relative position. Muscle contraction returns the head to its normal position. Immediately the balance of the body is maintained.

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.

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.

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.

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.

There are two openings in the middle ear. Fenestra ovalis (oval window) at the top and fenestra rotanda (round window) at the bottom. Sound enters the cochlea through the fenestra ovalis and exits through the fenestra rotanda.

Stepis looks triangular or like the stirrup of a horse saddle. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.

It looks like anvil. One end is attached to the malleus and the other end to the stapes

It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus

There are 3 small bones in the middle ear. These are-
(i) Malleus: It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus
(ii) Incus : It looks like anvil. One end is attached to the malleus and the other end to the stapes
(iii) Stepis: Stepis looks triangular or like the stirrup of a horse saddle. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.