Inner ear

Inner ear
The cochlea and vestibule, viewed from above.
Posterior Canal Superior Canal Utricle Horizontal Canal Vestibule Cochlea Saccule
Latin	auris interna
Gray's	subject #232 1047
Artery	labyrinthine artery
MeSH	Inner+ear

Inner ear

The inner ear is the bony labyrinth, a system of passages comprising two main functional parts:

• The cochlea is the hearing part of the inner ear.
• The semicircular canals , the utricle and the saccule are the balance (ability) part of the inner ear. This consists of three semicircular canals and the vestibule.

Inner ears are found in all vertebrates, with substantial variations in the form and function of their sensory organs. Each animal has two inner ears, one on each side of its head.

Ear overview, in context

In mammals, the outer ear focuses and directs sound waves into the middle ear. In the middle ear, the energy of these pressure waves is translated into mechanical vibrations of the middle ear’s bone structure. The cochlea of the inner ear 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 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.

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 bony labyrinth is lined with the membranous labyrinth. There is a layer of perilymph between them. The three parts of the bony labyrinth are the vestibule of the ear, the semicircular canals, and the cochlea.

Vestibular vs. cochlear

The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea (the hearing organ). 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 that control our balance.

Pathology

Interference with or infection of the labyrinth can result in a syndrome of ailments called Labyrinthitis. The symptoms of Labyrinthitis include temporary nausea, disorientation, vertigo, and dizziness. Labyrinthitis can be caused by viral infections, bacterial infections, physical blockage of the inner ear, or due to decompression sickness.^[1][2]

Anatomical details

Top image is antero-lateral and bottom image is postero-medial.

1. Lateral semicircular canal; 1’, its ampulla;
2. Posterior canal; 2’, its ampulla.
3. Superior canal; 3’, its ampulla.
4. Conjoined limb of superior and posterior canals (sinus utriculi superior).
5. Utricle. 5’. Recessus utriculi. 5”. Sinus utriculi posterior.
6. Ductus endolymphaticus.
7. Canalis utriculosaccularis.
8. Nerve to ampulla of superior canal.
9. Nerve to ampulla of lateral canal.
10. Nerve to recessus utriculi (in top image, the three branches appear conjoined). 10’. Ending of nerve in recessus utriculi.
11. Facial nerve.
12. Lagena cochleæ.
13. Nerve of cochlea within spiral lamina.
14. Basilar membrane.
15. Nerve fibers to macula of saccule.
16. Nerve to ampulla of posterior canal.
17. Saccule.
18. Secondary membrane of tympanum.
19. Canalis reuniens.
20. Vestibular end of ductus cochlearis.
21. Section of the facial and acoustic nerves within internal acoustic meatus (the separation between them is not apparent in the section).

Non-humans

Birds have an auditory system similar to that of mammals, including an outer ear, middle ear, and cochlea, though their middle ear has only one bone whereas the evolution of mammalian auditory ossicles resulted in three bones. Reptiles, amphibians, and fish do not have cochleas but hear with simpler auditory organs or vestibular organs, which generally detect lower-frequency sounds than the cochlea.

See also

• Labyrinth (inner ear)
• Vestibular system
• Cochlea

Additional images

Ear labyrinth

Inner ear

Temporal bone

Internal ear

References

External links

Wikimedia Commons has media related to: Inner ear

• SUNY Labs 30:05-0101

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