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 processorParts Pinna External ear EAC Middle ear TM Inner ear
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
Blood Supply Cranial surface - Posterior auricular A Lat surface - Anterior auricular A (Sup temp A)Nerve supply Greater auricular (C2-3) Lesser occipital (C2) Auricular branch of Facial (Concha) Auriculotemporal NLymphatic drainage Mastoid tip Pre-auricular Deep cervical
From bottom of concha to TM 24 mm along with post wall Lateral cartilaginous and medial bony partCartilage part Outer 1/3 (8 mm), deficient at Incisura terminalis (root of helix and tragus) Skin is thick with hairs and sebaceous and ceruminous glands (Apo-pilo-sebaceous Units) Fissures in ant wall ‘fissures of Santorini’Bony Part Medial 2/3 (16 mm) Two constrictions (Isthmus 5 mm lateral to TM) Ant recess sump for discharge Skin has no subdermal layer, firmly attached to periosteum
Has ceruminous glands in lateral 1/3rd Deficient in childrenBlood Supply Ext Carotid system (Sup temporal, Maxillary, Post auricular)Nerve supply Ant half Auriculotemporal N, post half by Arnold’s N (X)Relations Ant - TMJ Post - Mastoid Sup - Middle fossa Inf - Parotid gland
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
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
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°.
Separates auditory meatus of external ear from tympanic cavity of middle ear. Composed of four strata arranged in 3 general layers ◦ Outermost (cutaneous - ectoderm) very thin skin ◦ 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 ◦ Innermost (mucosa - endoderm) mucous membrane, with low cuboidal epithelium continuous with lining of tympanic cavity.
Landmarks Cone of Light Umbo Handle of Malleus Lat Process of Malleus A & P Malleolar Fold +/- Incus shadow Annulus
1. Lat part of EAC runs inwards, downwards and forwards. Ear pulled out, post and laterally2. Relatively less subcutaneous tissue makes the pinna more sensitive to frost bite3. Incisura terminalis is used for end-aural incision4. Referred otalgia5. Imp donor of cartilage and fat6. Isthmus holds the FB7. Vagus stimulation to increase appetite
8. Sagging of deep postero superior wall – Ac mastoiditis9. Furuncles only in lat part, very painful10. Persistent cough by impacted wax11. Cymba conchae direct relation to suprameatal triangle12. Skin has unique quality of migrating laterally