Inner ear

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The inner ear is the innermost part of the vertebrate ear. It consists of the bony labyrinth, a system of passages comprising two main functional parts:

The inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eighth cranial nerve in all vertebrates.


Divisions of labyrinth

The labyrinth can be divided by layer or by region.

Bony vs. membranous

The bony labyrinth, or osseous labyrinth, is the network of passages with bony walls lined with periosteum. The membranous labyrinth runs inside of the bony labryinth. There is a layer of perilymph fluid between them. The three parts of the bony labyrinth are the vestibule of the ear, the semicircular canals, and the cochlea.

Vestibular vs. cochlear

In the middle ear, the energy of pressure waves is translated into mechanical vibrations. The cochlea propagates these mechanical signals as waves in fluid and membranes, and finally transduces them to nerve impulses which are transmitted to the brain.

The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea. The vestibular system works with the visual system to keep objects in focus when the head is moving. Joint and muscle receptors also are important in maintaining balance. The brain receives, interprets, and processes the information from these systems to control balance.

The vestibular system of the inner ear is responsible for the sensations of balance and motion. It uses the same kinds of fluids and detection cells (hair cells) as the cochlea uses, and sends information to the brain about the attitude, rotation, and linear motion of the head. The type of motion or attitude detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals (otolith) of the saccule and utricle.

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