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Anatomy of middle ear

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Anatomy of middle ear

  1. 1. Presenter -Dr.Razal M Sherif Moderator -Dr.Jyothi Swarup R
  2. 2. THE MIDDLE EAR CLEFT • Eustachian Tube anteriorly • Middle ear Cavity/Tympanic Cavity • Aditus • Mastoid Antrum • Mastoid Air Cells posteriorly
  3. 3. Middle Ear Cavity • The tympanic cavity o irregular, air-filled space within the temporal bone o between the tympanic membrane laterally and the osseous labyrinth of inner ear medially. • Six sided Cavity o Roof o Floor o Anterior Wall o Posterior Wall o Medial Wall o Lateral Wall • Contains auditory ossicles ,Intratympanic Muscles
  4. 4. ROOF  Is a thin bony plate  separates the middle ear from the middle cranial fossa  called as Tegmen tympani  formed by both the petrous and squamous portions of the temporal bone .  Petrosquamous suture line,  does not close until adult life,  can provide a route of access for infection into the middle cranial fossa from middle ear in children.
  5. 5. FLOOR • Thin bone separates the cavity from the dome of the Jugular bulb. • In some cases the floor may be deficient and the jugular bulb is then covered only by fibrous tissue and a mucous membrane.
  6. 6. LATERAL WALL • Main part is formed By the Tympanic membrane. • Superiorly an area of Bone called SCUTUM (outer attic wall.)
  7. 7. ANTERIOR WALL • The lower-third of the anterior wall o consists of a thin plate of bone covering the internal carotid artery • The middle-third comprises o the tympanic orifice of the Eustachian tube, which is oval and 5 x 2mm in size.
  8. 8. MEDIAL WALL separates the Middle ear from the Inner ear. • Promontory- o bulging part of on the medial wall which overlies the basal turn of the cochlea o has small grooves on its surface containing the nerves which form the tympanic plexus. • Tympanic plexus
  9. 9. • Oval Window o Behind and above the promontory is the oval window o that connects the tympanic cavity with the vestibule, closed by the footplate of the stapes o it is 3.25 mm long and 1.75 mm wide. • Round window o RW membrane is usually out of sight, obscured by the overhanging edge of the promontory
  10. 10. Ponticulus & Subiculum • Two small bony projections are present on the medial wall, posterior to promontory. • Ponticulus o Is the upper projection posterosuperior to promontory. o Above the ponticulus is the Oval Window • Subiculum o Lower projection posteroinferior to promontory o Below the subiculum is the round window
  11. 11. • Facial Nerve canal (or Fallopian canal) o runs above the promontory and oval window in an anteroposterior direction. • Processus cochelariformis o a curved projection of bone on which the tendon of the tensor tympani muscle takes a hook and turns laterally to get attached to neck of malleus. o This forms the landmark for 1st genu of facial nerve – Posterosuperior to processus cochelariformis
  12. 12. POSTERIOR WALL • The posterior wall is wider above than below. • Aditus - A large irregular opening in its upper part • Fossa incudis – A small depression below the aditus, it houses the short process of the incus and its suspensory ligament. • Pyramid - a small hollow conical projection with its apex pointing anteriorly. o This houses the stapedius muscle and tendon, which inserts into the posterior aspect of the neck of stapes. o Nerve to stapedius runs through the hollow canal with in the pyramid.
  13. 13. Facial Recess & Sinus tymapni Facial recess - A 3D space situated between the • tympanic annulus and chorda tymapni laterally • Pyramid and vertical portion of facial nerve medially Sinus tympani – A 3D space situated between • Pyramid and vertical portion of facial nerve laterally • Ponticulus medially • Also extends deep to promontory • the most inaccessible site in the middle ear • Cholesteatoma which has extended to the sinus tympani is extremely difficult to eradicate
  14. 14. Division Of Middle Ear Cavity • EPITYMPANUM/ATTI C • MESOTYPANUM • HYPOTYMPANUM
  15. 15. EPITYMPANUM/ATTIC • Middle ear cavity above the level of anterior and posterior Malleolar folds • Contains o Head of Malleus, Body of incus, ossicular ligaments and Mucosal folds. Prussack Space • Space between Pars flacida laterally and Neck of Malleus medially. • It is the primary site of acquired Cholesteatoma
  16. 16. MESOTYPANUM • Part lying Medial to pars Tensa o and its air filled space o Conatins • handle of MALEUS • long process of Incus, • Stapes
  17. 17. HYPOTYMPANUM • Part lying below the lower margin of Tympanic membrane • Contains o Bulge produced by the jugular Bulb • If the floor is deficient thus jugular bulb may project into tympanic cavity.
  18. 18. Contents Of Middle Ear • Ossicles o Malleus o Incus o Stapes • Muscles of Tympanic Cavity o Tensor Tympani o Stapedius Muscle
  19. 19. The Malleus • Largest of the three ossicles - 9mm length • It Has Head, Neck, Anterior and Lateral Process, Handle o Suspended by the superior ligament between head and the tegmen tympani. • Head has saddle - shaped facet on its posteromedial surface o to articulate with the body of the incus. • An anterior ligament arises from the anterior process to insert into the petrotympanic fissure.
  20. 20. Head Neck Anterior Process Handle Lateral Process
  21. 21. The Incus • It has a Body, Short Process and a long process and a lenticular process • body of the incus o is suspended by the superior incudal ligament that is attached to the tegmen tympani. • Long process o extends downwards behind the handle of malleus o articulates with the head of the stapes by its lenticular process.
  22. 22. • Short process o Lodges in the fossa incudis • Lenticular process o Sometimes been called the fourth ossicle because of its incomplete fusion with the tip of the long process
  23. 23. Body Short Process Facet Lenticular Process Long Process
  24. 24. The Stapes • Shaped like a stirrup • Consists of a head, neck, the anterior and posterior crura and a footplate. • The Head points laterally and has a small cartilage- covered depression for a synovial articulation with the lenticular process of the incus • The foot plate directs medially and closes the Oval window. • Stapedius tendon inserts into the posterior part of the neck and upper portion of the posterior crus.
  25. 25. Anterior Crus Foot Plate Head Neck Posterior Crus
  26. 26. Tympanic Plexus • It lies over the promontory o Tympanic Branch of Glossopharygeal Nerve (Jacobsons Nerve) o Sympathetic fibers from plexus round internal carotid artery. • It supplies o Tympanic membrane(mucosal Surface) o Tympanic Cavity o Mastoid air cells o Bony estuation tube. o Carries secrtomotor fibers for parotid gland.
  27. 27. Chorda Tympani Nerve • Branch of Facial Nerve • Arises from the vertical segment of facial nerve below the pyramid • Crosses the posterior tympanic annulus • Runs over the posteror malleloar fold and in between the handle of the malleus and long process ,above the attachment of the tensor tympani • Leaves the middle ear through the canal of HUGAIER in the anterior wall • It carries the taste sensation from ant 2/3 of tongue and secretomotor fibers to sub maxillary and sub lingual salivary glands.
  28. 28. Muscles In the Tympanic Cavity • Tensor Tympani o Origin – • cartilaginous part of Eustachian tube • Bony canal over ET • greater wing of sphenoid. o Lies above the Eustachian tube • enters the middle ear via the canal for tensor tympani in the anterior wall above the Eustachian tube opening. o Hooks around the processes cochelariformis on the posterior wall and then changes the direction laterally and get inserted into neck of malleus. o Action • It tenses the tympanic membrane, by pulling the malleus medially and protects from barotrauma.
  29. 29. • Stapedius Muscle o Orgin - From the Pyramid in the posterior wall o Insertion - Neck Of Stapes o Supplied by Facial Nerve (Nerve to Stapideus) o Action - Pulls the Stapes Laterally (Prevents Barotrauma)
  30. 30. Mastoid Process And Air Cells • Mastoid Process o Part of temporal bone and situated behind the ear. o Development by 1 year. o Based on the degree of pneumatisations • Celluar – 80% - Fully pneumatised • Sclerotic – Cells are replaced by dense bones. • Diploeic – Cells are less and small.
  31. 31. o Mastoid antrum • Biggest and most consistent air cell • Connected anteriorly to tympanic cavity via the aditus and posteriorly to other air cells. • Relations o Roof – Tegment antri – seperates from middle cranial fossa. o Floor – Mastoid portion of temporal bone o Medial wall – Petrous portion of temporal bone o Lateral wall –Squamous portion of temporal bone
  32. 32. • Mac Ewans triangle o Landmark for mastoid antrum o Suprameatal crest above o Tangential to posterior meatal wall cutting the supra meatal crest o Posterior margin of EAC • Antrum lies postero superior spine of henle.
  33. 33. EUSTACHIAN TUBE • Connects middle ear cavity to nasopharynx. • From the anterior wall of middle ear it passes downwards, forwards and medially. • Length 36mm o Lateral 1/3rd Bony o Medial 2/3rd is cartilaginous. • The pharyngeal end situates 1cm behind and a little below the end of inferior turbinate.
  34. 34. • Functions of ET o In resting stage collapsed. On chewing and yawning it opens up. Helps to equalize air pressure between middle ear and nasopharynx. o Controls ventilation of middle ear cleft. o Helps drainage from middle ear. • Muscles attached to ET o Tensor tympani o Tensor palati o Levator palati o Salpingopharynx.

Editor's Notes

  • Cholesteatoma which has extended to the sinus tympani from the mesotympanum is extremely difficult to eradicate
  • Cholesteatoma -An abnormal squ epi growth in the middle ear, destroy the surrounding delicate bones of the middle ear,Conginital or acquired ,
  • This forms a chain to conduct the sound from the tympanic membrane to cochlea
  • incus by way of a synovial joint