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Middle ear. Middle ear structures Middle ear cavity/tympanum Middle ear cavity/tympanum Tympanic membrane Tympanic membrane Ossicles/Middle ear bones

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Text of Middle ear. Middle ear structures Middle ear cavity/tympanum Middle ear cavity/tympanum Tympanic...

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  • Middle ear
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  • Middle ear structures Middle ear cavity/tympanum Middle ear cavity/tympanum Tympanic membrane Tympanic membrane Ossicles/Middle ear bones Ossicles/Middle ear bones
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  • Middle ear cavity 2-4 mm horizontal, 13 mm vertical, approximately 2 cm 3 in volume 2-4 mm horizontal, 13 mm vertical, approximately 2 cm 3 in volume Comprised of Comprised of Tympanic cavity between outer and inner ear Tympanic cavity between outer and inner ear Epitympanic recess above the TM Epitympanic recess above the TM Mastoid recess contained in the mastoid region of the temporal bone Mastoid recess contained in the mastoid region of the temporal bone
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  • Tympanic cavity Similar to a box with six surfaces 1. Lateral wall or membraneous wall: Formed by TM and squamous portion of TB. 2. Medial wall or labyrinthine wall: Promontory (outer wall of inner ear) (oval and round windows, prominence of facial nerve) 3. Anterior wall or carotid wall (opening of ET and tendon of tensor tympani) 4. Posterior wall or mastoid wall (tympanic aditus, fossa incudis, pyramidal prominence, facial nerve through tympanic sulcus) 5. Inferior wall or jugular wall (tympanic plate of TB) 6. Superior wall or tegmental wall (tegmen tympani, continuing posteriorly to tympanic atrium)
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  • Tympanic membrane Oval shaped lateral surface Oval shaped lateral surface Thick periphery called annulus with the notch of Rivinus Thick periphery called annulus with the notch of Rivinus Located in a bony groove called tympanic sulcus Located in a bony groove called tympanic sulcus 8-9 horizontal, 9-10 mm vertical axis, 0.1 mm thick. 8-9 horizontal, 9-10 mm vertical axis, 0.1 mm thick. Held in place by fibers and cartilage Held in place by fibers and cartilage Cone shaped, translucent Cone shaped, translucent 55 to 90 mm 2 in area 55 to 90 mm 2 in area http://www.ghorayeb.com/AuricleEACAnatomy2.html
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  • Three layers Outer: Epidermis of EAM Inner: Mucosal lining of middle ear space Middle: Collagen fibers, support for TM. Middle layer composed of two sets of fibers: 1. Radiates outward from center 2. Concentric rings of fibers Two regions in tympanic membrane: Two regions in tympanic membrane: Superior region: Pars flaccida (defined by anterior and posterior malleolar folds and malleolar prominence) Superior region: Pars flaccida (defined by anterior and posterior malleolar folds and malleolar prominence) Inferior region: Pars tensa Inferior region: Pars tensa
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  • Tympanic membrane, contd. Umbo: Region of maximum concavity Umbo: Region of maximum concavity Position changes as EAM lengthens after birth Position changes as EAM lengthens after birth Important landmarks visible Important landmarks visible Tympanic membrane attached to ossicles. Tympanic membrane attached to ossicles. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html
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  • Ossicles 1. Malleus: Hammer 2. Incus: Anvil 3. Stapes: Stirrup http://www.ghorayeb.com/StapesPics.html http://www.ghorayeb.com/StapesPics.html Head of malleus and body of incus located in the epitympanic recess Head of malleus and body of incus located in the epitympanic recess http://oto.wustl.edu/bbears/ossicle.htm http://oto.wustl.edu/bbears/ossicle.htm http://oto.wustl.edu/bbears/ossicle.htm http://audilab.bmed.mcgill.ca/~daren/3Dear/mid1.html
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  • Malleus 9 mm long, 23-37 mg weight 9 mm long, 23-37 mg weight Head with articular facet Head with articular facet Neck Neck Anterior and lateral processes Anterior and lateral processes Handle or Manubrium Handle or Manubrium
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  • Incus About 23-32 mg weight About 23-32 mg weight Body Body Short crus/process in epitympanic recess, around 5 mm Short crus/process in epitympanic recess, around 5 mm Long crus/process with lenticular process, around 7 mm Long crus/process with lenticular process, around 7 mm (Plural of crus: Crura)
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  • Stapes 2-5 to 3.8 mm tall, 2.1 to 4.3 mg weight. Footplate area around 3.2 mm 2 2-5 to 3.8 mm tall, 2.1 to 4.3 mg weight. Footplate area around 3.2 mm 2 Head, with spine for attachment of stapedial tendon Head, with spine for attachment of stapedial tendon Neck Neck Two bony crura, anterior and posterior Two bony crura, anterior and posterior Flat oval bone called footplate Flat oval bone called footplate Medial surface of footplate fastened to wall of oval window by annular ligament. Medial surface of footplate fastened to wall of oval window by annular ligament. Unique connection allows for rocking, rather than piston- like, movement of stapes. Unique connection allows for rocking, rather than piston- like, movement of stapes.
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  • Ossicular connections Malleus: Manubrium of malleus connects to umbo of TM. Malleus: Manubrium of malleus connects to umbo of TM. Incus: Head of malleus connects to body of incus (incudo-mallear joint) Incus: Head of malleus connects to body of incus (incudo-mallear joint) Stapes: Inferior process of incus connects to form lenticular process, which connects to the stapes (incudo-stapedial joint) Stapes: Inferior process of incus connects to form lenticular process, which connects to the stapes (incudo-stapedial joint) Footplate of the stapes connects to the oval window Footplate of the stapes connects to the oval window
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  • Ossicular connections, contd. Suspended in the middle ear cavity by axial ligaments and muscle tendons Suspended in the middle ear cavity by axial ligaments and muscle tendons Middle ear muscles Middle ear muscles Tensor tympani and stapedius Tensor tympani and stapedius
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  • Tensor tympani Enters middle ear through anterior wall of tympanum. Enters middle ear through anterior wall of tympanum. Connected to manubrium/neck of the malleus Connected to manubrium/neck of the malleus Activated by the trigeminal nerve Activated by the trigeminal nerve Muscle runs parallel and superior to osseous foundation of the ET, separated by septum canalis musculotubarii) Muscle runs parallel and superior to osseous foundation of the ET, separated by septum canalis musculotubarii) Pulls malleus in anterior and posterior direction Pulls malleus in anterior and posterior direction
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  • Stapedius muscle Tendon enters the middle ear space through opening in the posterior wall of the tympanum (pyramidal eminence)Tendon enters the middle ear space through opening in the posterior wall of the tympanum (pyramidal eminence) Attached to the head of the stapesAttached to the head of the stapes Activated by the facial nerveActivated by the facial nerve Pulls stapes in the posterior directionPulls stapes in the posterior direction