Question

Write a short note on the cochlea.

Answer 1

Hint: The cochlea is a portion of the inner ear that looks like a snail shell.
It is a spiral-shaped cavity in the bony labyrinth. In humans, it makes 2.75 turns around its axis, the modiolus.

Complete answer: The cochlea is the part of the inner ear involved in hearing.
A core component of the cochlea is the Organ of Corti, the sensory organ of hearing.
The organ of Corti is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.
The cochlea is a spiraled, hollow, conical chamber of bone, in which waves propagate from the base (near the middle ear and the oval window) to the apex (the top or center of the spiral).

The cochlear structures include:
1. Three scalae or chambers: Also called vestibular duct or scala vestibule (containing perilymph), the tympanic duct, or scala tympani (containing perilymph), the cochlear duct or scala media (containing endolymph). The helicotrema that lies in the location where the tympanic duct and the vestibular duct merge, at the apex of the cochlea.
2. Reissner's membrane, which separates the vestibular duct from the cochlear duct.
3. The basilar membrane, a main structural element that separates the cochlear duct from the tympanic duct and determines the mechanical wave propagation properties of the cochlear partition.
4. The Organ of Corti which is the sensory epithelium, a cellular layer on the basilar membrane, in which sensory hair cells are powered by the potential difference between the perilymph and the endolymph.
Hair cells, sensory cells in the Organ of Corti that are topped with hair-like structures called stereocilia.

Note: The cochlea receives sound in the form of vibrations, which cause the stereocilia to move. The stereocilia then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted.