EXTERNAL EAR
EXTERNAL EAR
- External ear consists of following structures:
– Pinna/ Auricle
– External auditory canal (or external auditory meatus)
– Tympanic membrane (or eardrum)
EMBRYOLOGY:
- First branchial cleft is the precursor of external auditory canal.
- Around the sixth week of embryonic life, a series of six tubercles appear around the first branchial cleft.
- They progressively coalesce to form the auricle.
- Branchial clefts are ectodermal in origin.
- Pinna is formed at birth.
ANATOMY:
Skin
- Thin with no dermal palillae.
- Closely adherent to underlying cartilage & bony wall.
- Cartilagenous part has subcutaneous tissue -secretes wax.
- Active – collumnar & Quiescent – cuboidal
- Ceruminous glands and hair follicles are limited to cartilagenous parts only.
- Skin over pinna is fixed, Loosely on medial side.
Pinna/Auricle
- Irregularly concave, faces forwards with many eminences and depressions
- Helix
- Crus of helix
- Auricular tubercle (Darwin’s tubercle)
- Antihelix & its 2 cruras
- Triangular fossa
- Scaphoid fossa
- Concha & Cympa concha
- Tragus
- Antitragus
- Intertragic notch
- Lobule of pinna
Cartilagenous framework of auricle
- Single thin plate of elastic fibrocartilage (yellow)
- Continous with the cartilage of external auditory canal (EAC).
- No cartilage in lobule and between tragus and crus of the helix.
- Helix and antihelix are separated by fissura anti-tragohelicinia.
- Medial aspect has Eminentia concha & Eminentia scaphae separated by sulcus anti-helicis transversus
- E. conchae is crossed by a oblique ridge – Ponticulus
Ligaments
- Extrinsic – connects auricle to temporal bone
– Anterior Lig – tragus & spine of helix to root of zygomatic process
– Posterior Lig – post surf. of concha to lat. surf of mastoid process
- Intrinsic – connects individual auricular cartilages
– Strong fibrous band between tragus and helix
– Another band between antihelix and tail of helix
MUSCLES:
| TYPES | MUSCLES | NERVE SUPPLY | BLOOD SUPPLY | ACTION |
|
EXTRINSIC MUSCLES
|
|
|
Post. Auricular artery
|
|
|
INTRINSIC MUSCLES
|
|
|
Post auricular & superficial temporal artery | Minimal change in shape of auricle |
INNERVATION OF AURICLE
- Great Auricular Nr – most of medial surface & post. part of lateral surface (inclu. lobule)
- Lesser Occipital Nr – upper part of medial surface
- Auriculotemporal Nr – tragus, crus of helix & adjacent helix
- Auricular br of Vagus (Arnold’s Nr) & Facial Nr – Concha (lat.) & Eminentia concha (med.), post. auricular skin
- Pinna is supplied by Vagus nerve, Auriculotemporal nerve, Greater auricular nerve
Exam Important
- Pinna is ectodermal in origin
- Pinna is formed at birth
- Pinna is composed of a thin plate of yellow elastic cartilage, covered with integument
- Pinna develops from the cleft of Ist arch
- Sensory nerve supply of pinna is by V3
- Major part of the skin of pinna is supplied by Great auricular nerve
- Pinna is supplied by Vagus nerve, Auriculotemporal nerve, Greater auricular nerve
- Skin over pinna is fixed Loosely on medial side
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