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Gross Anatomy > Ear > Flashcards

Ear Flashcards

1
Q

External Features

A

• Auricle – directs sound to external acoustic meatus
• External Acoustic Meatus – directs sound to tympanic membrane
– Distal 1/3 = cartilage
– Proximal 2/3 = temporal bone
• Tympanic membrane – ear drum between external & middle ear
• Ear lobe

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2
Q

Middle Ear Cavity

A

• Tympanic cavity – air space within temporal bone (~ 10 x 10 x 6 mm)
– 2 continuous regions
• Tympanic cavity proper = medial to
tympanic membrane
• Epitympanic recess = superior to tympanic membrane
• Serves as relay center for sound waves – Between external & internal ear

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3
Q

Orientation in the Middle Ear Cavity

A

• Anteriorly – leads to auditory (Eustachian) tube – continues to nasopharynx
• Posteriorly – leads to aditus ad antrum
• Epitympanic recess = superior to tympanic
membrane
• Serves as relay center for sound waves – Between external & internal ear

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4
Q

Auditory Tube

A

• Anterior 2/3: cartilaginous & Posterior 1/3: bony (osseous)
– ~36 mm long
– Cartilaginous & bony portions meet at narrow isthmus
• Bony portion of tube opens at base of skull
• Only superior & Medial walls cartilaginous
• Inferior & Lateral walls membranous (mucosal)

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5
Q

Tegmen Tympani

A

• Superior border of middle ear cavity
– Separates middle ear from middle cranial
fossa
• Formed by the thin plate of petrous portion of the temporal bone
• Directly covers the epitympanic recess

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6
Q

Jugular wall (Floor)

A
  • Formed by thin plate of tympanic portion of the temporal bone
  • Separates the middle ear cavity from the jugular fossa
  • Fossa contains the superior jugular bulb of the IJV
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7
Q

Tympanic Membrane (lateral border of Middle Ear)

A

• Lower 5/6 fixed into bony ring called the tympanic sulcus
• Upper 1/6 of bony ring incomplete resulting in notch of
Rivinus
• Anterior & posterior malleolar folds secure the membrane in this region
• Superior to malleolar folds, membrane = parsflaccida
• Inferior to malleolar folds, membrane = parstensa

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8
Q

Inner Ear Labyrinth (medial border of Middle Ear)

A
  • Promontory = protuberance facing tympanic membrane
  • Fenstra vestibuli = oval window – receives base of stapes
  • Fenestra Cochlea = round window – membrane covered, inferior to oval
  • Facial canal prominence – contains facial n.
  • Lateral semicircular canal prominence
  • Tendon of the tensor tympani m.
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9
Q

Carotid Wall (anterior border of Middle Ear)

A

• Formed by thin plate of tympanic portion of the temporal bone
• Separates the middle ear cavity from the carotid canal
• 2 openings present in the superior aspect
– Auditory tube
– Semicanal for tensor tympani m.

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10
Q

Mastoid Wall (posterior border of Middle Ear)

A

• Pyramidal Eminence=hollow projection of bone
– Serves as origin of stapedius m.
• Aditus ad antrum=entrance to tympanic antrum
– Leads to post./infr. into mastoid air cells

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11
Q

Ossicles

A

• 3 auditory ossicles (bones)
– Malleus (hammer), incus (anvil), stapes (stirrup)
• Connect the tympanic membrane with the inner ear
• United by synovial joints & ‘suspended’ in cavity
– Via attachments to tympanic membrane, oval window & wall

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12
Q

Ossicle attachments

A

• Handle of Malleus (manubrium) – Attaches to inside of tympanic membrane
• Head of Malleus
– Within the epitympanic recess
• Incus
– Intervenes between the malleus & stapes
• Base of Stapes
– Attaches to the oval window

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13
Q

Muscles of Middle Ear

A

• Tensor tympani m.
• Stapedius m.
- Act to reduce oscillations of ossicles
- Protects inner ear from injury during loud noises

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14
Q

Tensor Tympani m.

A
  • Contained in bony semicanal – Superior to auditory tube
  • Runs posterior thru canal & then bends laterally
  • Inserts onto handle of malleus
  • Tenses tympanic membrane by drawing it medially
  • Innervated by CN V3
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15
Q

Stapedius m.

A
  • Smallest striated m. in body – ~ 1 mm
  • Arises from cavity inside pyramidal eminence
  • Inserts into neck of stapes
  • Pulls head of stapes posteriorly
  • Innervated by CN VII
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16
Q

Vessels of Middle Ear

A

• Arterial supply via tympanic branches of carotid branches
– All tympanic brs. are too tiny to dissect
– Anterior tympanic, inferior tympanic, superior tympanic, stylomastoid, & caroticotympanic aa.
• Venous drainage via accompanying vv. – Drain to superior petrosal sinus or
– Pterygoid plexus of vv.

17
Q

Innervation of Middle Ear

A

Facial n. (CN VII) & Facial canal
• CN VII enters facial canal & runs posteriorly
• Travels in medial wall of middle ear
• Canal passes over oval window & turns
inferiorly
• Then passes behind the round window
• Continues inferiorly to exit at the stylomastoid foramen

18
Q

Chorda Tympani

A

• CN VII sends of chorda tympani n. br. in facial canal
• It turns sharply upward to return to the middle ear cavity
• Enters the cavity thru posterior iter chordae
– Covered with mucosa

19
Q

Path of Chorda Tympani (Middle Ear -> Oral Cavity)

A
  • Ascends anteriorly thru middle ear cavity
  • Crosses medial surface of tympanic membrane
  • Passes between handle of malleus & incus
  • Exits cavity thru anterior iter chordae to petrotympanic fissure
  • Ultimately descends with Lingual n. into oral cavity
20
Q

Tympanic Plexus of nn.

A
  • Covers promontory in middle ear cavity
  • Runs under mucosal lining of cavity and supplies it
  • Supplies mastoid air cells and auditory tube
  • Formed by tympanic br. of CN IX (p-symp.)
  • Formed by cartoticotympanic nn. (symp.)
21
Q

Glosspharyngeal n. (CN IX)

A
  • Sends tympanic br. into middle ear cavity
  • Referred to as tympanic n. (of Jacobson)
  • Provides p-symp. & sensory
22
Q

Caroticotympanic n.

A
  • Derived from internal carotid plexus of nn.
  • Provides symp.to middle ear
  • Joins tympanic n. of CN IX to form tympanic plexus
23
Q

Greater Petrosal n.

A

• Br. off geniculate ganglion of CN VII
• Carries p-symp. fibers to pterygopalatine ganglion
• Joins deep petrosal n. (symp.) to form n. of pterygoid canal (vidian)
• Runs from hiatus of greater petrosal n. to pterygoid canal
– From petrous temporal toward foramen lacerum

24
Q

Lesser Petrosal n.

A

• Br. of tympanic plexus from CN IX
• Continuation from tympanic br. of CN IX
• Carries p-symp. fibers to otic ganglion (supplies parotid gl.)
• Runs from hiatus of lesser petrosal n. to foramen ovale
– Otic ganglion located below foramen ovale (medially)

25
Q

Features of Internal Ear

A

• Fluid-filled chamber for hearing & equilibrium
• Semicircular canals – controls balance & position
• Cochlea – controls hearing
• Oval window – beginning of cochlea (receives
stapes)
• Round window – end of cochlea (closed by membrane)
– Vibrates opposite oval window to perceive sound

Gross Anatomy (6 decks)

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