Question

Explain the structure of middle and internal ear with the help of diagram.

Answer 1

The middle ear contains three ossicles called the malleus, incus and stapes which are attached to one another in a chainlike fashion. The malleus is attached to the tympanic membrane and the stapes are attached to the oval window of the cochlea. The ear ossicles increase the efficiency of the transmission of sound waves to the inner ear. A Eustachian tube connects the middle ear cavity with the pharynx. The Eustachian tube helps in equalising the pressures on either side of the eardrum.

                          Diagrammatic view of the ear

• The fluid-filled inner ear called a labyrinth consists of two parts, the bony and the membranous labyrinths. The bony labyrinth is a series of channels. Inside these channels lies the membranous labyrinth, which is surrounded by a fluid called perilymph. The membranous labyrinth is filled with a fluid called endolymph. The coiled portion of the labyrinth is called the cochlea. The membranes constituting cochlea, the Reissner’s and basilar, divide the surrounding perilymph-filled bony labyrinth into an upper scala vestibuli and a lower scala tympani. The space within the cochlea called scala media is filled with endolymph. At the base of the cochlea, the scala vestibule ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear. The organ of Corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The hair cells are present in rows on the internal side of the organ of Corti. The basal end of the hair cell is in close contact with the afferent nerve fibres. A large number of processes called stereocilia are projected from the apical part of each hair cell. Above the rows of the hair cells is a thin elastic membrane called a tectorial membrane.
• The inner ear also contains a complex system called vestibular apparatus, located above the cochlea. The vestibular apparatus is composed of three semi-circular canals and the otolith (the macula is the sensory part of the saccule and utricle). Each semi-circular canal lies in a different plane at right angles to each other. The membranous canals are suspended in the perilymph of the bony canals. The base of the canals is swollen and is called the ampulla, which contains a projecting ridge called crista ampullar which has hair cells. The saccule and utricle contain a projecting ridge called a macula. The crista and macula are the specific receptors of the vestibular apparatus responsible for the maintenance of balance of the body and posture.

 

     

                    Diagrammatic representation of the sectional view of cochlea