anatomy and physiology of middle ear spaces

this ppt is about anatomy and physiology in brief mainly taken from standard test books and their is a mention of middle ear spaces in this ppt

1. ANATOMY AND PHYSIOLOGY OF MIDDLE EAR

2. EMBRYOLOGY OF MIDDLE EAR PHARYNGEAL POUCH:- PROXIMAL NARROW PART=EUSTACHIAN TUBE DISTAL DILATED PART=              1.TYMPANIC CAVITY              2.ANTRUM              3. ATTIC              4.MASTOID AIR CELLS OSSICLES=    1st ARCH CARTILAGE=1.HEAD OF MALLEUS                                              2.BODY OF INCUS     2nd ARCH CARTILAGE=1.HANDLE OF MALLEUS                                                2.LONG PROCESS OF INCUS                                                3.CRURA OF STAPES    OTIC CAPSULE=FOOT PLATE OF STAPES

3. Middle ear spaces Mucous membrane lines the bony walls of tympanic cavity and it extends to cover the ossicles and supporting ligaments Mucosal folds separate middle ear space in to compartments

4. Major mucosal folds Superior malleolar Lateral malleolar Lateral incudal Medial incudal Superior incudal Inter ossicular

5. COMPARTMENTS AND FOLDS OF TYMPANIC CAVITY: attic compartment: anterior compartment posterior compartment                        a)  superior incudal space                         b) medial incudal space   compartment of mesotympanum      1.anterior malleolar fold       2.posterior malleolar fold                                        

6. ISTHMUS TYMPANI ANTICUS : It lies between tensor tympani fold and crura of stapes. ISTMUS TYMPANI POSTICUS: Located near tip of short process of incus between posterior incudal ligament ,medial incudal fold , pyramid and stapedius muscle

7. Anterior pouch of vontroltsch : Between anterior malleolar fold and tympanic membrane anterior to handle of malleus Posterior pouch of vontroltsch : b/w post malleolar fold and T.M posterior to handle of malleus

8. Spread of cholesteatoma Posterior epitympanic cholesteatoma : Orginates at prussack’s space – lateral to ossicles – superior incudal space – aditus and antrum Posterior mesotympanic cholesteatoma : Orginate at post-sup quadrant of pars tensa – lies medial to ossicles – spread to involve facial recess and sinus tympani –reaches mastoid via posterior tympanic isthmus

9. Anterior epitympanic cholesteatoma : Orginate from epitympanic retraction anterior to head of malleus – reaches mesotympanum via anterior pouch of von troltsch – involve supra tubal recess – geniculate ganglion at risk

10. TYMPANIC CAVITY(MIDDLE EAR): DIVIDED IN TO 3 PARTS: EPITYMPANUM (ATTIC) MESOTYMPANUM HYPOTYMPANUM

11. LATERAL WALL OF MIDDLE EAR: FORMED BY    1.BONY LATERAL WALL OF EPITYMPANUM   2.TYMPANIC MEMBRANE    3.BONY LATERAL WALL OF HYPOTYMPANUM PETROTYMPANIC FISSURE:         RECIEVES:  ANTERIOR MALLEOLAR LIGAMENT  ANTERIOR TYMPANIC BRANCH OF MAXILLARY ARTEY CANAL OF HUGIER : MEDIAL WALL OF PETROTYMPANIC FISSURE THROUGH WHICH CHORDA TYMPANI RUNS OUT COURSE OF CHORSA TYMPANI

12. ROOF OF THE MIDDLE EAR: TEGMEN TYMPANI:  FORMED BY PETROUS AND SQUAMOUS PORTION OF TEMPORAL BONE PETOSQUAMOUS SUTURE:ROUTE OF INFECTION IN TO EXTRA DURAL SPACE IN CHILDREN   

13. ANTERIOR WALL OF MIDDLE EAR lower 1/3rd:- plate of bone covering carotid artery middle 1/3rd:-  1.eustachian tube  2.canal for tensor  tympani  upper 1/3rd:-has anterior epitympanic sinus anterior to ossicle heads&can hide cholesteatoma in canal wall up surgeries                                

14. POSTERIOR WALL:- aditus processus pyramidalis vertical portion of facial nerve facial  recess ( suprapyramidal recess) sinus tympani (infra pyramidal recess)

15. FLOOR OF MIDDLE EAR: formed by :- pneumatised bone separates from jugular bulb tympanic branch of glossopharyngeal nerve enters at junction between floor and medial wall

16. MEDIAL WALL OF THE MIDDLE EAR: three depressions: oval window  round window sinus tympani facial nerve canal dome of the lateral scc :-posterior and lateral to facial canal

17. MUCOSA OF TYMPANIC CAVITY:- mucous secreting resporatory ciliated epithelium ventilation route from mesotympanum and epitympanum is via two small openings anterior isthmus tympani posterior isthmus tympani prussak's space:- site for cholesteatoma       laterally=pars flaccida       medially  = neck of malleus       inferiorly=lateral process of malleus       superiorly=lateral malleolar fold

18. COMPONENTS OF TYMPANIC CAVITY: EAR OSSICLES : malleus = head,neck , anterior process, lateral process ,handle incus =body, short process, long process, lenticular process stapes= head,neck , anterior crura , posterior crura,foot plate long axis of stapes is always horizontal

19. MUSCLES OF MIDDLE EAR: tensor tympani stapedius :-supplied by a branch of mandibular nerve nerves: chorda tympani tympanic plexus

20. BLOOD SUPPLY OF MIDDLE EAR:- from branches of : middle meningeal artery maxillary artery ascending pharyngeal artery stylomastoid branch of posterior auricular artery nerve supply:- sensory:- ixth cranial nerve through tympanic plexus motor:- tensor tympani= mandibular division of vth nerve stapedius =facial nerve

21. intensity Defined as the power transmitted by sound wave through a unit area Intensity is dependent on pressure and velocity Intensity= peak pressure x peak velocity/2 Displacement produced by sound wave vary with frequency if intensity is constant Low frequency vibration produces greater displacement

22. Sound is alternate compression and rarefraction of air 2 properties of sound: intensity and frequency

23. IMPEDANCE Impedance is defined as resistance offered by a medium for transmission of sound

24. DECIBEL Measurement of sound level It is logarithmic unit of measurement that express the magnitude of physical quantity of sound ,relative to reference level A difference of 1 db is the minimum perceptive change in volume of sound

25. FUNCTIONS OF MIDDLE EAR 25

26. MIDDLE EAR FUNCTIONS Couples sound energy to cochlea Provide physical protection for cochlea It serves as an acoustic transformer to match the impedance of air to the much higher impedance of the cochlear fluids It couple sound preferably to only one window of the cochlea , thus producing differential pressure between windows ,required for the movement of cochlear fluids

27. MODE OF VIBRATING MIDDLE EAR STRUCTURES TYMPANIC MEMBRANE: It moved to and fro, it is buckled in the regions between manubrium of malleus and the , anterior and posterior edges. Inferior edges T.M – vibration greatest

28. in high frequencies above 6kHz, the pattern becomes much more complex, vibration breaks up in to many small zones with the reduction in efficiency of transfer of vibration.

29. The axis of rotation of the ossicles and the axis of suspension by their ligaments coincide with their centre of rotational inertia , so bones vibrate with very little loss through suspending ligaments

30. Movement of stapes up to 1 kHz – stapes foot plate moves primarily like a piston Higher frequencies : vibration become more complex , with rotatory motion along both the long and short axis of the foot plate

31. IMPEDANCE TRANSFORMER middle ear acts as impedance transformer It transfers the incoming vibrations from large low impedance T.M to much smaller, higher impedance ,oval window.

32. Impedence transformer will change the low pressure , high displacement vibration of air into high pressure , low displacement vibrations suitable for driving the cochlear fluids

33. Impedence mismatch IF THERE WAS NO MIDDLE EAR SYSTEM ,99% OF SOUND WAVES WOULD HAVE REFLECTED BACK FROM OVAL WINDOW MIDDLE EAR BY ITS IMPEDENCE MATCHING PROPERTY ALLOWS 60% OF SOUND ENERGY TO DISSIPATE IN INNER EAR 33

34. (a) HYDRAULIC ACTION OFTYMPANIC MEMBRANE Total effective area of tympanic membrane 45mm2 Area of stapes footplate is 3.2mm2 Effective areal ratio is 14:1 Thus by focusing sound pressure from large area of tympanic membrane to small area of oval window the effectiveness of energy transfer between air to fluid of cochlea is increased 34

35. (b) Lever action of ossicles Handle of malleus is 1.3 times longer than long process of incus Overall this produces a lever action that converts low pressure with along lever action at malleus handle to high pressure with a short lever action at tip of long process of incus 35

36. (c) Action of tympanic membrane Eustachian tube equilibrates the air pressure in middle ear with that of atmospheric pressure, thus permitting tympanic membrane to stay in its most neutral position . A buckling motion of tympanic membrane result in an increased force and decreased velocity to produce a fourfold increase in effectiveness of energy transfer 36

37. PHASE DIFFERENTIAL EFFECT Sound waves striking the tympanic membrane do not reach the oval and round window simultaneously. There is preferential pathway to oval window due to ossicular chain. This acoustic separation of windows is achieved by intact tympanic membrane and a cushion of air around round window This contributes 4dB when tympanic membrane is intact 37

38. INFLUENCE OF MIDDLE EAR MUSCLES 2 muscles in the middle ear Tensor tympani muscle Stapedius muscle Tensor tympani muscle : Insertion : It inserts on to the top of manubrium of malleus medially Action : it pulls malleus medially and anteriorly , nearly at right angles to the normal direction of vibration

39. STAPEDIUS MUSCLE: Insertion : inserts on the posterior aspect of stapes Action : pulls stapes posteriorly Muscles affect the transmission of sound in 2 ways By increasing the stiffness of ossicular chain By changing the direction of vibration of ossicles so that movement is less effectively coupled to cochlea

40. middle ear muscles contract in response to sounds In humans only stapedius can be driven acoustically , unless the sound is loud enough to give a startle reflex To start a reflex, the stimuli be 80 db above subject’s absolute threshold in the frequency range from 250 kHz to 4 kHz

41. FUNCTION OF MIDDLE EAR MUSCLE Middle ear muscle reflex protects from noise damage ,but the reflex is too slow to protect the ear from sudden impulsive noise ,but have effect on longer lasting noise Reflex causes selective attenuation of low frequency components in high intensity speech thereby improving intelligibility of speech Reflex reduces the influence of resonances in the middle ear

42. Thank you