Ear.txt

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emm64
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116952
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Ear.txt
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2011-11-15 03:01:36
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Ear HN
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Ear HN
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  1. External Ear
    • auricle
    • external acoustic (or auditory) meatus
    • lateral wall of the tympanic membrane
    • V3 (auriculotemporal n.)
    • cervical plexus (great auricular n.)
    • area of the concha may receive sensory innervation (SA) from CN VII and X
  2. auricle:
    • 1. helix
    • 2. antihelix
    • 3. tragus
    • 4. antitragus
    • 5. scaphoid fossa
    • 6. concha
    • 7. lobule
  3. External Acoustic Meatus
    opening leading from the auricle to the tympanic membrane
  4. Tympanic Cavity Diagram
  5. Tympanic Membrane
    “the ear drum” is an oval disc (0.1 mm thick) which separates the external acoustic meatus from the tympanic (middle ear) cavity.
  6. Tympanic (Middle Ear) Cavity
    • irregularly shaped air-filled space located medial to the tympanic membrane
    • lies between the external and internal ear
    • mucosa of the middle ear cavity is innervated by sensory fibers (VA) of CN IX
  7. malleus
    • bony ossicle attached to the medial surface of the tympanic membrane.
    • Note that the tensor tympani muscle attaches to the handle of the malleus and the cartilage of the auditory tube and helps to dampen excessive vibration.
  8. tensor tympani muscle
    • attaches to the handle of the malleus and the cartilage of the auditory tube and helps to dampen excessive vibration.
    • innervated by a branch of the trigeminal nerve V3 division.
  9. stapes
    footplate or base of the stapes lies in the “oval window” (on the medial wall of the tympanic cavity) where it contacts directly the perilymphatic fluid of the inner ear.
  10. Bony Ossicles
    • malleus, incus, and stapes
    • Sound waves cause the tympanic membrane to vibrate.
    • The vibration of the tympanic membrane causes the 3 auditory ossicles to move.
    • As the footplate or base of the stapes moves, it causes waves or current changes in the perilymphatic fluid of the inner ear.
    • These fluid movements are detected by “hair cells” of the inner ear which convert this energy into neural impulses which are sent to the brain via cranial nerve VIII – the vestibulocochlear nerve.
  11. lateral wall
    • tympanic cavity (membranous wall)
    • formed by the tympanic membrane.
    • It is crossed by the chorda tympani nerve (a branch of cranial nerve VII – the facial nerve) which carries taste fibers to the anterior 2/3rds of the tongue and VE-para/pre fibers to the submandibular ganglion (via the lingual nerve – a branch of V3).
  12. chorda tympani nerve
    (a branch of cranial nerve VII – the facial nerve) which carries taste fibers to the anterior 2/3rds of the tongue and VE-para/pre fibers to the submandibular ganglion (via the lingual nerve – a branch of V3).
  13. medial wall tympanic cavity
    • (labyrinthine wall) separates the middle ear cavity from the internal ear. On this wall there is a bony elevation called the promontory.
    • There are also 2 “windows” – the oval (vestibular) window and the round (cochlear) window.
    • The footplate or base of the stapes occupied the oval window. The round window is covered by a membrane.
  14. Tympanic Plexus
    • On this promontory is a nerve plexus called “the tympanic plexus”.
    • This plexus is formed by the tympanic branch of CN IX (the glossopharyngeal nerve) and sympathetic fibers.
    • The VE-para/pre fibers from CN IX in the plexus reform as the “lesser petrosal nerve” which leaves the middle ear cavity and petrous bone to travel on the floor of the middle cranial fossa where it dives inferiorly through the foramen ovale to join the otic ganglion.
    • The lesser petrosal nerve is thus bringing VE-para/pre fibers from CN IX to the otic ganglion.
    • From the otic ganglion, Ve-para/post fibers will be sent, via the auriculotemporal nerve (a branch of V3), to the parotid gland.
  15. tensor tympani muscle.
    • This muscle attaches to the handle of the malleus and acts to dampen the vibration.
    • The tensor tympani muscle is innervated by a branch of V3 (mandibular division of the trigeminal nerve).
  16. anterior wall tympanic cavity
    • (carotid wall) is bounded by a thin layer of bone that separates the tympanic cavity from the internal carotid artery.
    • There is also a canal for the tensor tympani muscle.
    • This muscle attaches to the handle of the malleus and acts to dampen the vibration.
    • The tensor tympani muscle is innervated by a branch of V3 (mandibular division of the trigeminal nerve).
    • The auditory (Eustachian) tube also opens onto the anterior wall and connects the middle ear cavity with the pharynx.
    • The tube functions to equalize pressure in the middle ear with the atmospheric pressure in order to allow the free movement of the tympanic membrane.
  17. auditory (Eustachian) tube
    • opens onto the anterior wall and connects the middle ear cavity with the pharynx.
    • The tube functions to equalize pressure in the middle ear with the atmospheric pressure in order to allow the free movement of the tympanic membrane.
  18. aditus
    "doorway or entrance to tymapnic or mastoid antrum
  19. mastoid antrum
    chamber lined with mastoid air cells
  20. pyramidal eminence
    attachement site for stapedius muscle which attaches to the stapes and dampens vibration
  21. stapedius muscle
    • attaches to stapes and pyramidal eminence to dampen vibration
    • innervated by CN VII- facial nerve branchial motor fibers
  22. facial canal
    transmits facial nerve as it courses inferiorly to the stylomastoid foramen to form the 5 motor brances to muscles of facial expression
  23. chorda tympani nerve
    • course along lateral wall of tympanic cavity
    • exits middle ear cavity by pasisng through petrotympanic fissure which opens into the infratemporal fossa.
  24. posterior wall tympanic cavity
    (mastoid wall) contains a “doorway” or entrance (aditus) to the tympanic or mastoid antrum which is a chamber that is lined with mastoid air cells. There is also a bony pyramid called the “pyramidal eminence” which serves as an attachment site for the stapedius muscle which attaches to the stapes and acts to dampen vibration. This muscle is innervated by CN VII – the facial nerve (branchial motor fibers). Inside the posterior wall is the facial canal which transmits the facial nerve as it courses inferiorly to the stylomastoid foramen to form the 5 motor branches to muscles of fascial expression. As it passes through this vertical canal, it will give off the chorda tympani nerve which courses along the lateral wall of the tympanic cavity. The chorda tympani will exit the middle ear cavity by passing through the petrotympanic fissure which opens into the infratemporal fossa.
  25. roof tympanic cavity
    (the tegmental wall) is a thin plate of bone that separates the tympanic cavity from the middle cranial fossa.
  26. floor tympanic cavity
    (the jugular wall) is a narrow convex plate of bone that lies between the tympanic cavity and the bulb of the internal jugular vein.
  27. Internal Ear
    contains the cochlear and vestibular labyrinths which are concerned with the reception of sound and the maintenance of balance, respectively. These labyrinths have a bony and membranous component.
  28. Bony Labyrinth
    series of cavities composed of 3 parts: cochlea, vestibule, and semicircular canals.
  29. Membranous Labyrinth
    • consists of a series of communicating sacs and ducts that are suspended in the bony labyrinth.
    • It contains endolymph, a watery fluid that differs from the perilymph that fills the remainder of the bony labyrinth. There are 3 parts of the membranous labyrinth:
    • 1. utricle and saccule – 2 small communicating sacs in the vestibule of the bony labyrinth
    • 2. 3 semicircular ducts in the semicircular canals – there are sensors in the semicircular duct & ampulla system for recording the movements of the endolymph resulting from movement of the head (this system is the organ for balance)
    • 3. cochlear duct in the cochlea – the spiral organ of Corti (hearning organ) is situated on the floor of the duct.

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