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CSD 3103 anatomy of speech and hearing mechanisms Hearing mechanisms Fall 2008 The Middle Ear.

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Presentation on theme: "CSD 3103 anatomy of speech and hearing mechanisms Hearing mechanisms Fall 2008 The Middle Ear."— Presentation transcript:

1 CSD 3103 anatomy of speech and hearing mechanisms Hearing mechanisms Fall 2008 The Middle Ear

2 The middle ear Important Structures: — Epitympanic recess — Tympanic cavity — Aditus ad antrum — Mastoid air cells — Ossicles

3 The middle ear Schematic view of the middle ear boundaries and landmarks

4 The superior face u Tegmen Tympani

5 The inferior face  Tympanic plate  Jugular fossa

6 The medial face  Oval window  Footplate of the stapes  Round window  Promontory

7 The lateral face  Eardrum

8 The posterior face Mastoid wall Tympanic aditus Pyramidal eminence Chorda tympani nerve

9 The anterior face Carotid wall Eustachian tube

10 General structures of the middle ear  Eardrum  Ossicular chain  Eustachian tube  Middle ear muscles

11 The ossicles  Malleus (hammer)  Incus (anvil)  Stapes (stirrup)

12 The malleus  Manubrium  Neck  Head  Lateral process

13 The malleus

14 The incus  Short process  Long process  Lenticular process  Incudostapedial joint

15 The incus

16 The stapes  Head  Neck  Anterior crus  Posterior crus  Footplate

17 The stapes

18 Articulated ossicular chain

19 Ossicles on a dime

20 Ligaments of the ossicular chain  Superior malleal ligament  Anterior malleal ligament  Lateral malleal ligament  Posterior incudal ligament

21 The ossicular chain in place

22 Purpose of the ossicuar chain  Impedance matching  Protection

23 Ossicular motion

24 Vibratory motion of The stapes

25 Impedance matching of the middle ear  a sound wave traveling in a medium of certain physical properties, namely density and elasticity, will not pass readily into a medium with different properties  the more different the characteristics of the two media are, the more sound energy will be reflected at the boundary

26 Impedance matching of the middle ear  Acoustic resistance of air: 41.5 ohms  Acoustic resistance of cochlear fluid: 161,000 ohms  This represents a ratio of 3880:1  Without the impedance matching capabilities of the middle ear, only 1/10 of 1% of the energy of an incoming sound wave would make it into the cochlea--99.9% of the energy would be reflected at the boundary

27 Area advantage  The area of the tympanic membrane is 17x the oval window  As the area decreases, the pressure increases

28 Impedance matching of the middle ear  Area advantage  Curved membrane buckling

29 Curved membrane buckling Notice how the eardrum curves from its rim at both ends to its attachment with the malleus in the middle. This point of the eardrum (V 1 ) doesn’t move as far. This causes an increase in force.

30 Impedance matching of the middle ear  Area advantage  Curved membrane buckling  Lever action

31 Lever action advantage  The advantage is increased in (B) when the fulcrum is moved closer to the mass to be lifted.

32 Purpose of the ossicuar chain  Impedance matching  Protection

33 Purpose of the ossicuar chain The acoustic reflex Tensor tympani muscle Stapedius muscle

34 The tensor tympani  Larger of the two tympanic muscles  Tendon leaves the bony wall via the cochleariform process

35 The stapedius  The smaller of the two tympanic muscles  Tendon leaves the bony wall via the apex of the pyramidal eminence

36 The acoustic reflex  It is a reflex  Bilateral  Occurs in response to sound intensities delivered to either ear at dB above threshold

37 The eustachian tube  mm long  Oriented downward, forward, medialward  Osseous portion  Cartilaginous portion  Isthmus  Tensor palatini muscle

38


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