External acoustic meatus

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External acoustic meatus
Anatomy of the human ear.
Latin	meatus acusticus externus
Gray's	subject #229 1036
Artery	anterior auricular branches
Precursor	groove (cleft) of the first branchial arch.[1]
Dorlands/Elsevier	m_06/12518132

The ear canal (external auditory meatus, external acoustic meatus), is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum and is about 26 mm in length and 7 mm in diameter.

Contents 1 Size and shape 2 Disorders 3 Earwax 4 References 5 Additional images 6 External links

[edit] Size and shape

The human ear canal is approximately 26 mm long and 7 mm in diameter. Size and shape of the canal vary among individuals. This is an important factor to consider when fitting hearing protectors.

[edit] Disorders

The ear canal, because of its relative exposure to the outside world, is a common victim of diseases and other disorders. Some disorders include:

• Otitis externa (swimmer's ear), bacteria-caused inflammation of the ear canal
• Contact dermatitis of the ear canal
• Ear fungus
• Ear myiasis, an extremely rare infestation of maggots
• Bone exposure, caused by the wearing away of skin in the canal
• Granuloma, a scar usually caused by tympanostomy tubes
• Stenosis, a gradual closing of the canal
• Foreign body in ear
• Ear mites in animals.

[edit] Earwax

Main article: Earwax

Earwax, also known as cerumen, is a yellowish, waxy substance secreted in the ear canals. It plays an important role in the human ear canal, assisting in cleaning and lubrication, and also provides some protection from bacteria, fungi, and insects. Excess or impacted cerumen can press against the eardrum and/or occlude the external auditory canal and impair hearing.

[edit] References

1. ^ hednk-022 — Embryology at UNC

[edit] Additional images

Base of skull. Inferior surface.

Left infratemporal fossa.

External and middle ear, opened from the front. Right side.

Horizontal section through left ear; upper half of section.

[edit] External links

• Veterans Health Administration web site
• OSHA web site
• Continuing Medical Education Ear Photographs
• Otoscopy Tutorial w/ Images
• Roche Lexicon - illustrated navigator, at Elsevier 34257.000-1

v • d • e Sensory system: Auditory and Vestibular systems Outer ear Pinna (Helix, Antihelix, Tragus, Antitragus, Earlobe) • Ear canal Middle ear Eardrum (Umbo) • Ossicles (Malleus, Incus & Stapes) • muscles (Stapedius, Tensor tympani) • Eustachian tube (Torus tubarius) Inner ear/Labyrinth Bony labyrinth (Vestibule) • Membranous labyrinth Oval window → Scala vestibuli / Reissner's/vestibular membrane, Helicotrema and Scala tympani / Basilar membrane (Perilymph) → Round window Cochlea: Modiolus • Cochlear duct / scala media (Endolymph, Stria vascularis, Spiral ligament, Organ of Corti), Olivocochlear system Organ of Corti: Stereocilia • Sulcus spiralis (externus, internus) • Limbus spiralis to brain (auditory) Tectorial membrane → Hair cells → Spiral ganglion → Cochlear nerve VIII → Cochlear nuclei → Trapezoid body → Superior olivary nuclei → Lateral lemniscus → Inferior colliculi → Medial geniculate nuclei → Auditory radiations → Primary auditory cortex Vestibular system Static/translations: Utricle (Macula) – Saccule (Macula, Endolymphatic sac, Endolymphatic duct) – Kinocilium – Otolith Kinetic/rotations: Semicircular canals (Superior, Posterior, Horizontal) • Cupula • Ampullae (Crista ampullaris) to brain (vestibular) Vestibular nerve VIII → Vestibular nuclei, Flocculonodular lobe Vestibular nuclei → Vestibulospinal tract, Ventral posterolateral nucleus → Vestibular cortex

v • d • e Foramina of the skull (and canals, fissures, meati, and hiati) Anterior cranial fossa to Orbit: ethmoidal foramina (anterior, posterior) to Nasal cavity: olfactory foramina (CN-I) - foramen cecum Middle cranial fossa to Orbit: optic canal (CN-II) - superior orbital fissure (CN-III,IV,V1,VI) to Pterygopalatine fossa: foramen rotundum (CN-V2) - pterygoid canal to Infratemporal fossa: foramen ovale (CN-V3) - foramen spinosum/carotid canal other: foramen lacerum - hiatus for greater petrosal nerve - hiatus for lesser petrosal nerve - sphenoidal emissary foramen Posterior cranial fossa internal auditory meatus/facial canal/stylomastoid foramen (CN-VII,VIII) - jugular foramen (CN-IX,X,XI) - foramen magnum (CN-XI) - hypoglossal canal (CN-XII) - condylar canal - mastoid foramen Orbit to Nasal cavity: nasolacrimal canal to Face: supraorbital (notch, foramen) - infraorbital (foramen, groove) - zygomatic foramen (-facial, -temporal) to Pterygopalatine fossa: inferior orbital fissure Pterygopalatine fossa to Nasal cavity: sphenopalatine foramen to Oral cavity: greater palatine canal/greater palatine foramen - lesser palatine canals/lesser palatine foramina to Infratemporal fossa: pterygomaxillary fissure to Nasopharynx: palatovaginal canal Nasal cavity to Oral cavity: incisive canals - incisive foramen Other external acoustic meatus - mandibular foramen - mental foramen - parietal foramen - petrotympanic fissure - semilunar hiatus