Ear
General
Anatomy, histology & grossing
Author: Nat Pernick, M.D.
Last author update: 1 October 2013
Last staff update: 17 April 2021
Copyright: 2002-2024, PathologyOutlines.com, Inc.
PubMed Search: Ear anatomy [title]
Table of Contents
Definition / general | External ear - anatomy | External ear - histology | Middle ear - anatomy | Middle ear - histology | Inner ear - anatomy | Inner ear - histology | GrossingCite this page: Pernick N. Anatomy, histology & grossing. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/earnormalanatomy.html. Accessed April 20th, 2024.
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
External and middle ear
External, middle and inner ear
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
Inner wall of middle ear
Eustachian tube
Chain of ossicles
Malleus
Incus
Stapes
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
Cochlea and surrounding structures
Cochlea cross section
Floor of cochlea
Spiral organ of Corti
Semicircular canal cross section
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
