External ear
Auris externa
Also known as: outer ear
The auricle and external acoustic meatus, which collect sound, funnel it to the tympanic membrane, amplify speech frequencies by resonance and protect the eardrum.
Overview
The external ear extends from the auricle to the lateral surface of the tympanic membrane. Together the concha and ear canal act as a resonator: a tube ≈2.5 cm long closed at one end resonates at a quarter-wavelength of ≈3 kHz, boosting sound pressure at the eardrum by ≈10–15 dB in the 2–4 kHz range — exactly the frequencies important for speech consonants.
The folds of the auricle filter incoming sound in a direction-dependent way (head-related transfer function), providing the spectral cues needed for vertical localisation and front–back discrimination; horizontal localisation depends on interaural time and level differences processed in the brainstem.
The canal is self-cleaning: the skin of the tympanic membrane and canal migrates outwards, carrying cerumen (wax) with it. Cerumen is acidic, water-repellent and antimicrobial.
- Location
Side of the head; from the auricle to the tympanic membrane.
Parts & subdivisions
- Elastic-cartilage framework covered by skin.
- S-shaped canal ≈2.5 cm long leading to the tympanic membrane.
Anatomy
- Innervation
Auriculotemporal (V3), great auricular (C2–C3), lesser occipital (C2), auricular branch of vagus (X), sensory twigs of the facial nerve (VII).
- Arterial supply
Posterior auricular, superficial temporal and deep auricular arteries.
- Lymphatic drainage
Preauricular (parotid), mastoid (retroauricular) and superficial cervical nodes.
- Development
First pharyngeal cleft (meatus) and the six auricular hillocks of the first and second arches (auricle).
Function
- Collect and funnel sound waves
- Resonate (≈2–4 kHz), boosting pressure at the eardrum by ≈10–15 dB
- Provide spectral cues for sound localisation
- Protect the tympanic membrane (cerumen, hairs, canal curvature)
Clinical significance
Otitis externa
Inflammation of the canal skin ("swimmer's ear"), commonly Pseudomonas aeruginosa or Staphylococcus aureus: itch, pain on moving the tragus, discharge. Necrotising (malignant) otitis externa — Pseudomonas osteomyelitis of the skull base in elderly diabetics or immunocompromised patients; granulation tissue on the canal floor and cranial nerve palsies (VII first).
Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.