Dr.P.KARTHIKEYAN, D.L.O.,DNB(ENT),PROFESSOR AND HEAD OF ENT,

MGMCRI, PONDICHERRY.

PARTS OF EXTERNAL EAR MIDDLE EAR CLEFT PARTS OF TYMPANIC MEMBRANE CONTENTS OF MIDDLE EAR TYMPANIC PLEXUS TYPES OF MASTOID AND MACEWEN’S

TRIANGLE. PARTS OF INNER EAR PATHWAY OF HEARING

Parts of the Ear• Ear can be divided into 3 parts:Ear can be divided into 3 parts:

• External earExternal ear• Middle earMiddle ear• Inner earInner ear

Layers of TM: outer epithelial layer middle fibrous layer inner mucosal layer Nerve supply: Branches of auriculotemporal nerve. Auricular branch of vagus. Tympanic branch of glossopharyngeal

nerve.

Irregular air filled space within temporal bone between TM laterally and osseous labyrinth medially.

Contains- 3 ossicles 2 muscles chorda tympani tympanic plexus 3 compartments: epitympanum mesotympanum hypotympanum

CHORDA TYMPANI: Enters the tympanic cavity from the

posterior canaliculus at the junction of the posterior and lateral wall.

Runs across the medial surface of the TM.

Pass medial to the upper border of handle of malleus above the tendon of tensor tympani continues forward and leaves by way of anterior canaliculus.

TYMPANIC PLEXUS: Tympanic branch of glossopharyngeal

nerve & carotico tympanic nerves form a plexus on the promontory.

They provide branches to mucous membrane lining tympanic cavity, ET, mastoid antrum and air cells.

Anterio inferiorly – Ciliated columnar epithelium with lot of goblet cells and mucous glands.

Postero superiorly – Cuboidal epithelium with less glands.

Epitympanum – Pavement or flat epithelium.

Functions of mastoid air cells:- air reservoir for middle ear.- insulating chambers, protecting

labyrinth from temperature variation.- Resonance to sound.

Perilymph – similar to extracellular fluid. It contains more Na+ and less K+. It derived from CSF.

Endolymph – similar to intracellular fluid. It contains more K+ and less Na+. It derived from dark cells of stria vascularis.

Cortilymph – similar to perilymph.