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Structure

Ear

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The ear is the organ of hearing and balance, divided into external, middle and inner parts. The external and middle ear conduct and amplify sound; the inner ear contains the cochlea for hearing and the vestibular apparatus for balance.

Terminologia Anatomica (Latin): Auris · Open in the 3D atlas

Location

The auricle and external acoustic meatus lie on the side of the head; the middle ear (tympanic cavity) and the inner ear are within the petrous part of the temporal bone, the middle ear communicating with the nasopharynx through the auditory tube and with the mastoid air cells.

Structure

External ear: auricle, meatus and tympanic membrane. Middle ear: tympanic cavity with the malleus, incus and stapes (footplate in the oval window), the tensor tympani and stapedius muscles, and the auditory tube. Inner ear: bony labyrinth (cochlea, vestibule, three semicircular canals) containing the membranous labyrinth with endolymph, the organ of Corti, the maculae of utricle and saccule, and the cristae of the ampullae.

Blood supply

External ear: posterior auricular and superficial temporal arteries. Middle ear: branches of the maxillary (anterior tympanic, middle meningeal) and stylomastoid arteries. Inner ear: the labyrinthine (internal auditory) artery, usually a branch of the anterior inferior cerebellar artery (sometimes of the basilar), an end-artery with little collateral supply.

Innervation

Hearing and balance are carried by the vestibulocochlear nerve (VIII), with cochlear and vestibular divisions. The tympanic plexus (glossopharyngeal) supplies the middle-ear mucosa; the auricle is supplied by the great auricular, lesser occipital, auriculotemporal and auricular branch of the vagus; tensor tympani by V3 and stapedius by the facial nerve.

Function

Sound is collected by the auricle, transmitted by the tympanic membrane and ossicular chain with impedance matching to the cochlear fluids, and transduced by hair cells of the organ of Corti with tonotopic organisation. The utricle and saccule sense linear acceleration and gravity; the semicircular canals sense angular acceleration.

Clinical correlations

Conductive hearing loss (wax, otitis media with effusion, perforation, otosclerosis) differs from sensorineural loss (presbycusis, noise, ototoxic drugs, vestibular schwannoma); Rinne and Weber tests help distinguish them. Acute otitis media may spread to the mastoid or intracranially. Vertigo may be due to BPPV, vestibular neuritis, or Ménière disease; facial palsy may complicate middle-ear disease.

Common exam points

  • Ossicles: malleus, incus, stapes; the stapes footplate sits in the oval window.
  • Tensor tympani is supplied by V3 and stapedius by the facial nerve (hyperacusis in facial palsy).
  • Labyrinthine artery arises usually from AICA; it is an end-artery, so ischaemia causes sudden hearing loss and vertigo.
  • Rinne and Weber tests separate conductive from sensorineural hearing loss.
  • Vestibular schwannoma arises on CN VIII at the cerebellopontine angle.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Kandel ER, Koester JD, Mack SH, Siegelbaum SA. Principles of Neural Science. McGraw-Hill, 6th edition (2021) — Tier 3 (textbook)

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