Ear

General

Anatomy, histology & grossing



Topic Completed: 1 October 2013

Minor changes: 17 April 2021

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Ear anatomy [title]


Nat Pernick, M.D.
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Cite this page: Pernick N. Anatomy, histology & grossing. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/earnormalanatomy.html. Accessed December 8th, 2021.
Definition / general
  • Sense organ for hearing and balance
  • Divided into external ear, middle ear and temporal bone and inner ear
  • External ear conducts sound vibrations to tympanic membrane; middle ear conducts sound to auditory portion of inner ear
External ear - anatomy
  • Consists of pinna (auricle) leading into external auditory canal which ends at tympanic membrane
  • Pinna: develops from fusion of auricular hillocks, themselves from first and second branchial areas; helix is prominent rim; antihelix is prominence that is parallel with and in front of helix
  • External auditory canal: S shaped passage, 2.5 cm long, develops from remnant of first branchial groove; has outer cartilaginous portion and inner osseous portion
  • Tympanic membrane: develops from first and second branchial pouches and first branchial groove


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Lateral surface of pinna

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External and middle ear

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External, middle and inner ear

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Tympanic membrane

External ear - histology
  • Pinna: resembles skin elsewhere with keratinized, stratified squamous epithelium, dermal adnexal structures, subcutaneous fibroconnective tissue, fat and elastic fibrocartilage which provides support
  • External auditory canal: lined by thin keratinized stratified squamous epithelium covering scant fibrous stroma along entire canal and covering external tympanic membrane
    • Outer third contains ceruminous glands (modified apocrine glands) deep within dermis that produce cerumen; glands are in clusters of cuboidal cells with intensely eosinophilic cytoplasm with apical snouts and containing golden yellow, granular pigment and secretory droplets along luminal border; glands are surrounded by myoepithelial cells; outer canal contains cartilage not bone
    • Inner two thirds has very thin epidermis which lacks rete pegs, no / reduced number of ceruminous glands and dermal adnexa; contains bone not cartilage
  • Cerumen: watery fluid devoid of lipids; drains from glands into ducts which open into hair sacs of ear canal hairs; fluid mixes with sebaceous gland secretions to produce cerumen (wax)
  • Tympanic cavity: thin fibrous structure lined by attenuated keratinizing squamous epithelium on external canal side
Middle ear - anatomy
  • Also called tympanic cavity
  • Filled with air (via eustachian tube); contains chain of movable bones which convey vibrations communicated to tympanic membrane across the middle ear cavity to the internal ear
  • Lateral aspect is tympanic membrane and squamous portion of temporal bone
  • Medial aspect is petrous portion of temporal bone
  • Superior aspect is tegmen tympani, a thin plate of bone separating middle ear space from cranial cavity
  • Inferior aspect is thin plate of bone separating tympanic cavity from superior bulb of internal jugular vein
  • Anterior aspect is thin plate of bone separating tympanic cavity from carotid canal containing internal carotid artery
  • Posterior aspect is petrous portion of temporal bone containing mastoid air cells and mastoid antrum
  • Develops from invagination of first branchial pouch (pharyngotympanic tube) from primitive pharynx
  • Contains auditory ossicles (malleus, incus, stapes), eustachian tube, tympanic cavity, epitympanic recess, mastoid cavity, chorda tympani of facial nerve (cranial nerve VII)
  • Malleus and incus develop from mesoderm of first branchial arch (Meckel cartilage), stapes develops from mesoderm of second branchial arch (Reichert cartilage)
  • Connects to pharynx through Eustachian tube
  • Connects with mastoid cavity through contiguous pneumatic spaces


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Tympanic membrane

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Inner wall of middle ear

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Eustachian tube

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Chain of ossicles


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Malleus

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Incus

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Stapes

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Temporal bone

Middle ear - histology
  • Eustachian tube: respiratory epithelium that becomes pseudostratified as it approaches nasopharynx; lymphoid component, prominent in children, is called Gerlach tubal tonsil; no glands
  • Tympanic membrane: thin fibrous structure lined by flat, single layer of cuboidal epithelium on middle ear side
  • Mastoid: flat, single, cuboidal epithelium
  • Ossicles: typical synovial joints
Inner ear - anatomy
  • Located in medial (petrous) portion of temporal bone
  • Contains cochlea (sense organ for hearing) and vestibular labyrinth (sense organ for balance with membranous and osseous portions) and internal auditory canal (contains vestibulocochlear nerve, CN VIII)
  • Vestibular labyrinth contains semicircular canals, includes blind endolymphatic sac, located in petrous bone
  • Endolymphatic sac is connected to utricle and saccule by endolymphatic duct which passes along petrous bone
  • Develops before middle and external ear at end of first month of gestation
  • References: Wikipedia: Cochlea [Accessed 4 January 2019]


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Labyrinth

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Cochlea and surrounding structures

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Cochlea cross section

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Floor of cochlea


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Spiral organ of Corti

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Semicircular canal cross section

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Endolymphatic sac (ES) and duct (ED)

Inner ear - histology
  • Vestibular labyrinth is lined by flat to low columnar epithelium overlying vascular stroma
Grossing
  • Orientation is essential; may need to consult with surgeon, particularly if middle ear or inner ear tissue is present
  • Must determine surgical resection margins
  • Extensive decalcification may be needed
  • Stapes: orient for embedding after decalcification to reveal outline of entire ossicle
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