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Cross-section through the spiral organ of Corti at greater magnification, showing position of the hair cells on the basement membrane. The organ of Corti is located in the scala media of the cochlea of the inner ear between the vestibular duct and the tympanic duct and is composed of mechanosensory cells, known as hair cells. [2]
It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. [2] [3] A core component of the cochlea is the organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.
Cross-section through the spiral organ of Corti at greater magnification. Rosenthal's canal or the spiral canal of the cochlea is a section of the bony labyrinth of the inner ear that is approximately 30 mm long and makes 2¾ turns about the modiolus, the central axis of the cochlea that contains the spiral ganglion.
Unlike structures of the inner and middle ear, which develop from pharyngeal pouches, the ear canal originates from the dorsal portion of the first pharyngeal cleft. [18] [20] It is fully expanded by the end of the 18th week of development. [21] The eardrum is made up of three layers (ectoderm, endoderm and connective tissue).
The cochlear duct (a.k.a. the scala media) is an endolymph filled cavity inside the cochlea, located between the tympanic duct and the vestibular duct, separated by the basilar membrane and the vestibular membrane (Reissner's membrane) respectively.
The organ of Corti is located in this duct on the basilar membrane, and transforms mechanical waves to electric signals in neurons. The other two sections are known as the scala tympani and the scala vestibuli. These are located within the bony labyrinth, which is filled with fluid called perilymph, similar in composition to cerebrospinal fluid.
There are two different types of fluid that surround the hair cells of the inner ear. The endolymph is the fluid that surrounds the apical surfaces of hair cells. Potassium is the major cation in the endolymph and is thought to be responsible for carrying the receptor currents in the cochlea .
While the semicircular canals respond to rotations, the otolithic organs sense linear accelerations. Humans have two otolithic organs on each side, one called the utricle, the other called the saccule. The utricle contains a patch of hair cells and supporting cells called a macula. Similarly, the saccule contains a patch of hair cells and a macula.