Middle ear

MIDDLE EARSOOREJ JAIBOI K

MIDDLE EAR• Narrow air filled cavity• Lined by mucous membrane

• Middle ear extends beyond the limits of tympanic membrane and is divided into

1. Mesotympanum

2. Epitympanum

3. Hypotympanum

• Contain 3 auditory ossicles –transmit sound vibration from tympanic membrane in its lateral wall to the internal ear

Size and shape• Like a cube • Compressed from side to side

MEASUREMENTS • VERTIAL DIA - 15MM• ANTEROPOSTERIOR DIA - 15MM• TRANSVERSE DIA• AT THE ROOF - 6MM• IN THE CENTRE - 2MM• AT THE FLOOR - 4MM

COMMUNICATION • ANTERIORLY -with nasopharynx

• Posteriorly - with mastoid antrum and mastoid air cells

CONTENTS• AIR

• OUTSIDE THE MUCOUS LINNING

3 small bone-malleus ,incus , stapes

2 muscles – tensor tympani ,stapedius

2 nerve - chorda tympani and tympanic plexus

Vessel supplying and draining the middle ear

Ligament of the ear ossicle

BOUNDARIES

1. ROOF• Formed by tegmen tympani

• Separates tympanic cavity from middle cranial fossa

• Extend posteriorly to form roof of aditus and antrum

2. FLOOR• Formed by thin plate of bone

• Separatethe tympanic cavity from jugular bulb

• Tympanic branch of glossopharyngeal nerve pierces the floor b/w jugular fossa and lower opening of carotid canal

ANTERIOR WALL• Thin plate of bone • Separate the cavity from internal carotid artery• Has two opening

1. Upper one for the canal of tensor tmpani muscle

2. Lower one for the Eustachian tube

POSTERIOR WALL• Separate the tympanic cavity from mastoid antrum and mastoid air cells • It has the features like

ADITUS AD ANTRUM

• Opening in upper part thru which tympanic cavity communicate with mastoid antrum

2 .PYRAMID – hollow bony projection containing stapedius muscle

3 .VERTICAL PART OF FACIAL CANAL -run in post. Wall just behind the pyramid and descend upto the stylomastoid foramen

4.Posterior canaliculus for chorda tympani

MEDIAL WALL• Separate the tympanic cavity from internal ear• Medial wall presents

1.Oval window 2. round window 3. sinus tympani 4. promontory 5. prominence of oblique part facial canal 6. prominence of lateral semicircular canal of the internal ear

LATERAL WALL• Formed by tympanic membrane • Separate the tympanic cavity from the external auditory meatus

EAR OSSICLE MALLEUS • resemble hammer• Has head ,neck , handle ,lateral process and anterior process• Develped from first pharyngeal arch cartilage • Muscle attached –tensor tympani

INCUS• Anvil • Developed – first pharyngeal arch cartilage

STAPES• Stirrup• Developed – first pharyngeal arch cartilage

•

ARTERIAL SUPPLY1. ANTERIOR TYMPANIC BRANCH OF MAXILLARY ARTERY2. STYLOMASTOID BRANCH OF POST. AURICULAR ARTERY3. PETROSAL BRANCH OF MIDDLE MENINGEAL ARTERY4. SUPERIOR TYMPANIC BRANCH OF MIDDLE MENINGEAL ARTERY5. ARTERY OF PTERYGOID CANAL 6. TYMPANIC BRANCH OF INTERNAL CAROTID ARTERY

VENOUS DRAINAGE1. Pterygoid venous plexus

2. Superior petrosal sinus

LYMPHATIC DRAINAGE

1. Retropharyngeal lymph node

2. Parotid lymph node

3. Upper deep cervical lymph node

NERVE SUPPLY 1. Tymphanic branch of glossopharyngeal nerve 2. Sup and inf. Caroticotymphanic nerve3. Facial nerve4. Mandibular nerve

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