Anatomy of the External Ear Dr Supreet Singh

Anatomy of the External Ear Dr. Supreet Singh Nayyar, AFMC MS (ENT) For more presentations, visit www. nayyar. ENT. com

Parts of the Ear • External Ear • Middle Ear (Cleft) • Inner Ear

ANATOMY OF THE EAR • Hearing is a primitive sense and is essential in all animals • Well developed and well protected • It needs a sound source, conducting mechanism, end organ and a central processor Pinna Parts EAC Ø External ear Ø Middle ear Ø Inner ear TM

EXTERNAL EAR

Auricle (Pinna) • Projects from the side of the head (shape size and angle varies) • Shape maintained by a yellow elastic cartilage (one piece of cartilage forming pinna and external part of EAC, except lobule) • Covered with skin • Several elevations and depressions

AURICLE

AURICULAR CARTILAGE

Auricle (Pinna) Blood Supply Ø Cranial surface - Posterior auricular A Ø Lat surface - Anterior auricular A (Sup temp A) Nerve supply Ø Greater auricular (C 2 -3) Ø Lesser occipital (C 2) Ø Auricular branch of Facial (Concha) Ø Auriculotemporal N Lymphatic drainage ØMastoid tip ØPre-auricular ØDeep cervical

PINNA NERVE SUPPLY

PINNA NERVE SUPPLY

EXTERNAL AUDITORY CANAL • From bottom of concha to TM • 24 mm along with post wall • Lateral cartilaginous and medial bony part Cartilage part Ø Outer 1/3 (8 mm), deficient at Incisura terminalis (root of helix and tragus) Ø Skin is thick with hairs and sebaceous and ceruminous glands (Apo-pilo-sebaceous Units) Ø Fissures in ant wall ‘fissures of Santorini’ Bony Part Ø Medial 2/3 (16 mm) Ø Two constrictions (Isthmus 5 mm lateral to TM) Ø Ant recess sump for discharge Ø Skin has no subdermal layer, firmly attached to periosteum

EAC

EXTERNAL AUDITORY CANAL Ø Has ceruminous glands in lateral 1/3 rd Ø Deficient in children Blood Supply Ø Ext Carotid system (Sup temporal, Maxillary, Post auricular) Nerve supply Ø Ant half Auriculotemporal N, post half by Arnold’s N (X) Relations Ø Ø Ant Post Sup Inf - TMJ Mastoid Middle fossa Parotid gland

CERUMINOUS GLANDS • Simple, tubular, coiled structure having myoepithelium • Secretions expressed into root canal • Watery white secretion initially dries up and gets oxidised and becomes sticky and dark in colour • Modified sweat glands and react to same stimuli as other apocrine glands. Ad, fever, stress ↑ secretions

Ceruminous and sebaceous glands

WAX • Mixture of secretions of ceruminous and sebaceous glands • Two types dry and wet • Dry wax – yellowish or grey, dry and white • Wet wax – yellowish brown, wet and sticky • Contains amino acids, fatty acids, lysozymes and immunoglobulins. • Has a bactericidal activity • Migrates outside but may get impacted

Tympanic Membrane • The external ear canal describes an S - like pathway from the entrance to the TM. • The TM separates the external ear canal from the middle-ear cavity and is inserted at an angle of approximately 55°.

Tympanic Membrane • Separates auditory meatus of external ear from tympanic cavity of middle ear. • Composed of four strata arranged in 3 general layers o Outermost (cutaneous - ectoderm) very thin skin o Middle (connective tissue - mesoderm) • Radiate (radiatum) fibroelastic connective tissue • Circular (circulare) fibroelastic connective tissue • In the Pars flaccida the radiate and circular layers are extremely thin and considered absent • Annulus fibrosus o Innermost (mucosa - endoderm) mucous membrane, with low cuboidal epithelium continuous with lining of tympanic cavity.

TYMPANIC MEMBRANE • Landmarks Ø Cone of Light Ø Umbo Ø Handle of Malleus Ø Lat Process of Malleus Ø A & P Malleolar Fold Ø +/- Incus shadow Ø Annulus

TYMPANIC MEMBRANE ON OTOSCOPY

Tympanic Membrane - Quadrants

APPLIED ANATOMY 1. 2. 3. 4. 5. 6. 7. Lat part of EAC runs inwards, downwards and forwards. Ear pulled out, post and laterally Relatively less subcutaneous tissue makes the pinna more sensitive to frost bite Incisura terminalis is used for end-aural incision Referred otalgia Imp donor of cartilage and fat Isthmus holds the FB Vagus stimulation to increase appetite

APPLIED ANATOMY 8. Sagging of deep postero superior wall – Ac mastoiditis 9. Furuncles only in lat part, very painful 10. Persistent cough by impacted wax 11. Cymba conchae direct relation to suprameatal triangle 12. Skin has unique quality of migrating laterally

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