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Otology & Neurotology > Anatomy & Physiology & Embryology - look at all pictures > Flashcards

Anatomy & Physiology & Embryology - look at all pictures Flashcards

1
Q

√Name the 5 embryological parts of the temporal bone

A
  1. Squamous
  2. Petrous
  3. Tympanic
  4. Mastoid
  5. Styloid

https://scontent.fxds1-1.fna.fbcdn.net/v/t1.6435-9/43754159_1034149063433256_7539316296396046336_n.png?_nc_cat=107&ccb=1-7&_nc_sid=730e14&_nc_ohc=UF6kA96to10AX9VT2XQ&_nc_ht=scontent.fxds1-1.fna&oh=00_AfCZE0jYHaKVhiXjrdkA264dCqGL8V8F9nBTO80CvRVmKg&oe=6517624B

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2
Q

What is McEwan’s Triangle and what are its boundaries?

A

aka. Suprameatal Triangle
Definition: Landmark to identify the location of the mastoid antrum (usually around 1-2cm deep to this triangle)

Superior: Inferior temporal line from the posterior root of zygomatic arch of the squamous temporal bone

Anterioinferior: Tangent extending up from the posterosuperior border of the EAC, including the suprameatal spine of henle

Posterior: Tangential line connecting the two

https://specialist-ent.com/wp-content/uploads/2020/11/MACEWENS-TRIANGLE.png

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3
Q

What does the temporal line serve as a landmark for?

A

Dura of the middle cranial fossa. Temporal line is ~5mm below the level of the dura.

https://entokey.com/wp-content/uploads/2016/06/B9780323052832001282_gr1.jpg

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4
Q

√Define the elements of a cross-section of the internal auditory canal (IAC). What do these nerves innervate?

A

Anterior-Superior: Facial Nerve & Nervus Intermedius
Anterior-inferior: Cochlear nerve
Postero-superior: Superior vestibular nerve
Postero-inferior: Inferior vestibular nerve

SVN innervates Superior SCC, horizontal SCC, and utricle
IVN innervates posterior SCC and saccule

Bill’s Bar separates AS to PS
Falciform crest separates superior from inferior

https://prod-images-static.radiopaedia.org/images/4183/1cbfb49d3ebc2068c28f5713a6d0a3_gallery.jpeg

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5
Q

√Describe the embryology of the auricle/external ear

A

Auricle begins development around 3-5 weeks GA

Arises from the 6 Hillocks of His, from the first and 2nd branchial arches
Reach adult form (but not size) by 18th week

  • First branchial Arch (Hillocks 1-3)
    Hillock 1: Tragus
    Hillock 2: Helical crus
    Hillock 3: Ascending helix, concha cyma
    (2+3 = Helix)
  • Second branchial Arch (Hillocks 4-6)
    Hillock 4: Horizontal/descending helix, scapha
    Hillock 5: Anti helix, scapha (antihelix?)
    (4+5 = Antihelix)
    Hillock 6: Anti tragus

https://entokey.com/wp-content/uploads/2016/06/B9780323052832001932_gr1.jpg

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6
Q

√Label all the parts of the external ear
Triangular fossa
Anterior crus
Helical crus
Posterior crus
Helical root
Meatus
Tragus
Antitragus
Incisura (space between tragus and antitragus)
Intertragal notch
Lobe
Darwin’s tubercle
Scaphoid fossa
Helix
Antihelix
Concha Cymba
Concha
Concha Cavum

A

See Kevan’s Otology questions #6

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7
Q

√What is the EAC anatomy composed of?

A

1/3 outer is cartilage
2/3 medial is bony
Isthmus = bone cartilaginous junction, the narrowest part of the EAC

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8
Q

√What embryological structure does the EAC derive from? How does the EAC form embryologically?

A

First Branchial cleft/arch

4th week GA - 1st arch invaginates over next 4 weeks, ectoderm forms a **core of tissue **that comes into apposition with endoderm of 1st pouch (which becomes middle ear mucosa).

28th week GA - Epithelial core canalizes from medial to lateral to form the EAC. Failure of recanalization results in aural atresia

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9
Q

√List 3 paths for tumoral/infection spread from the EAC

A
  1. Bone-cartilaginous junction
  2. Fissures of Santorini - lateral, cartilaginous defects in the EAC (fissures for cartilage)
  3. Foramen of Huschke - Medial, bony defect in the EAC (foramen for bone)

https://www.otoscape.com/assets/eponyms/fissures-of-santorini/foramen-huschke-fissures-santorini.png

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10
Q

√What are the normal dimensions of the adult ear? What are some landmarks you can use?

A

Height = 5.5-6.5cm (~6)
Width = 55% height
Protrusion = 1.5-2cm (15-30 degree angle from head)
Inclination = 20 degree posterior tilt

Landmarks: Superior helix should be at the level of the lateral brow, root of helix should be level of lateral canthus

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11
Q

√What is Hitselberger’s sign?

A

Numbness of the area of the EAC (postero-superior choncha) innervated by the posterior auricular branch of CNVII, suggests a space occupying lesion in the IAC

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12
Q

√What are the motor and sensory nervous innervation of the external ear?

A

Motor: Temporal branch of CNVII

Sensory:
a. Great auricular nerve (from cervical plexus, C2-C3).
b. Auriculotemporal nerve (from V3)
c. Posterior auricular nerve (from VII)
d. Arnold’s nerve - auricular branch of vagus (from X)
e. Lesser occipital nerve (cervical plexus C2-C3

Page 4 of Kevan’s Otology notes

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13
Q

√Describe the vascular supply to the outer ear

A

Arterial: (“TOP”)
1. Superficial Temporal artery
2. Occipital artery
3. Posterior auricular artery

Venous: (“TEP”)
1. Superficial temporal vein
2. External jugular vein
3. Posterior auricular vein

https://imgv2-1-f.scribdassets.com/img/document/363470526/original/a398181808/1692003182?v=1

https://juniperpublishers.com/gjo/images/GJO.MS.ID.555630.G006.png

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14
Q

√What is Arnold’s Reflex?

A

Stimulation of the concha/EAC elicits a cough due to stimulation of the area innervated by Arnold’s nerve (branch of CNX)

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15
Q

√What is Jacobsen’s nerve? What role does it play in referred otalgia?

A

Branch of the glossopharyngeal nerve that travels over the promontory in the middle ear.

Also known as the tympanic plexus.

Referred otalgia is caused by pharyngeal pathology that activates CNIX sensors that cross signal with Jacobsen’s branch

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16
Q

√Name the extrinsic muscles of the ear

A

ASP:
1. Anterior auricular (origin: lateral edge of the epicranial aponeurosis, inserts: front of helix)
2. Superior auricular (origin: epicranial aponeurosis, inserts: upper part of medial surface of the auricle)
3. Posterior auricular (origin: mastoid part of temporal bone, inserts: lower part of the cranial surface of the auricle of the outer ear)

https://media.springernature.com/lw685/springer-static/image/chp%3A10.1007%2F978-3-030-16387-7_1/MediaObjects/435423_1_En_1_Fig2_HTML.png

https://upload.wikimedia.org/wikipedia/commons/6/62/Sobo_1909260-_Auricularis_anterior.png

https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Sobo_1909260-_Superior_auricular_muscle.png/500px-Sobo_1909260-_Superior_auricular_muscle.png

https://upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Auricularis_posterior.png/250px-Auricularis_posterior.png

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17
Q

√Describe the intrinsic muscles of the ear

A

2 Helicis, 2 Tragus, 2 directional

Helicis major
Helicis minor
Tragicus
Antitragicus
Transverse auricular
Oblique auricular

Page 5 Kevan’s notes

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18
Q

√Label all parts of a TM. How can you tell which ear is which?

A

Ear orientation: lateral process of malleus points anterior. Once ossicles are removed, pyramidal eminence and stapes tendon lie at the posterior superior wall.

  1. Long process of the incus
  2. Posterior malleolar fold
  3. Pars flaccida
  4. Lateral process of malleus
  5. Anterior malleolar fold
  6. Manubrium (handle) of malleus
  7. Cone of light (on pars tensa)
  8. Annulus
  9. Umbo
  10. Promontory
  11. Chorda tympani

See Page 5 Kevan’s notes

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19
Q

√Label the parts of the ossicles

A

See image from Otology half day Kevan’s lecture

1_Anatomy and Physiology of the Ear

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20
Q

√Describe the layers of the tympanic membrane and their embryological origin.

A
  1. Outer epithelial layer
    Ectodermal origin
    Stratified squamous epithelium
    Arises from 1st branchial cleft
  2. Middle fibrous layer
    Mesoderm origin
    Outer radial and inner circular fibrous connective tissue (radiate out, circle in) - counts as two layers
  3. Inner mucosal layer
    Endodermal origin
    1st branchial pouch
    Squamous epithelial mucosa

See image Vancouver notes page 217

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21
Q

√What is the blood supply to the tympanic membrane?

A

Arteries of the lateral surface:
1. Deep auricular artery: branch off the IMAX, forms the peripheral vascular ring around the TM
2. Manubrial artery: branch of deep auricular artery, travels along the manubrium.

Arteries of the medial surface:
1. Anterior tympanic artery: branch off the IMAX
2. Stylomastoid branch: off posterior auricular artery

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22
Q

√Label the middle ear structures after the ossicles have been removed

A

see Kevan notes page 6

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23
Q

√What are the borders of the sinus tympani?

A

Lateral: Pyramidal eminence/facial nerve
Medial: Medial wall of the middle ear, posterior SCC
Superior: Ponticulus (bridge of bone from pyramidal eminence to promontory)
Inferior: Subiculum (bony ridge formed by posterior extension of promontory, separates oval and round windows)

Kevan Page 7

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24
Q

√Describe the classical interpretation of the embryology of the ossicles

A

First pharyngeal arch = malleus and incus
Second pharyngeal arch = stapes

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25
Q

√Describe the detailed embryology of the stapes

A

6th week GA: Develops just between malleus & incus formation. Stapes structure and middle ear portion forms from the mesoderm of the second pharyngeal arch (Reichert’s cartilage) and supplied by the stapedial artery (runs through). Otic portion of the footplate and annular ligament derived from the otic capsule.

8th week GA: Incudostapedial joint forms. The 2 diarthrodial ossicular joints form.

10th week GA: Stapedial artery degenerates. Stapes starts forming its adult shape

16-25th week: Ossification of the stapes occurs from medial to lateral

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26
Q

√Describe the Dual-Arch Interpretation of the Embryology of the ossicles

A

First pharyngeal arch = Meckel’s Cartilage
- Forms the epitympanic ossicles, including the head of malleus, body of the incus, and incus short process

Second pharyngeal arch = Reichert’s cartilage
- Forms the mesotympanic ossicles, including manubrium of malleus, long process and lenticular process of incus, and stapes superstructure.

Stapes footplate arises from the otic capsule

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27
Q

√What types of joints are present in the ossicular chain?

A
  1. Incudomallear articulation: Synovial joint, diarthrodial (fully mobile), interarticular disc
  2. Incudostapedial articulation: Synovial joint, diarthrodial, no interarticular disc
  3. Stapediovestibular articulation (between the stapes and oval window): Amphiarthrodial (slightly mobile), syndesmosis (fibrous joint held with ligaments)
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28
Q

√What are the structural and functional classifications of joints?

A

Functional classification:
1. Synarthrosis - immovable
2. Amphiarthrosis - slightly movable
3. Diarthrosis - freely movable

Structural classification:
1. Fibrous joint - connected by fibrous tissue (includes syndesmosis)
2. Cartilaginous joint - connected by cartilage
3. Synovial joint - connected by a joint capsule filled with lubricating fluid

All synovial joints are free movable.
Fibrous or cartilaginous joints may be immovable or slightly movable.

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29
Q

√What are the boundaires of the middle ear/tympanic cavity?

A

Superior: Tegmen
Inferior: Jugular bulb, internal carotid artery, styloid prominence
Lateral: Tympanic membrane, scutum
Medial: Medial wall, Promontory and Labyrinth, Tympanic FN segment
Anterior: Carotid, Eustachian Tube, tensor tympani, Cochleariform process
Posterior: Sinus tympani, pyramidal eminence, Stapedial tendon and stapedius muscle, Facial recess, Mastoid

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30
Q

√Describe the blood supply to the middle ear

A
  1. Internal maxillary artery
    - Deep auricular artery - supplies lateral TM and inferior portion of the medial surface of the middle ear
    - Manubrial artery (branch off deep auricular) supplies manubrium
    - Anterior tympanic artery - has 3 branches, supplies lateral wall of epitympanum, ossicles
  2. Middle meningeal artery
    - Superior tympanic artery - supplies epitympanum, tensor tympani, stapes
    - Superficial petrosal artery - supplies dura, geniculate ganglion of the facial nerve
  3. Ascending pharyngeal artery
    - Inferior tympanic artery - supplies floor of middle ear, promontory
  4. Posterior auricular artery
    - branches to Stylomastoid artery –> bone and mucosa of the mastoid, floor and inferoposterior wall of middle ear, facial nerve, stapedius muscle
    - Posterior tympanic artery (branches from the stylomastoid artery) –> chorda tympani
  5. Accessory meningeal artery
    - Branches to Tubal artery - supplies ET
  6. Caroticotympanic arteries
    - From the petrous portion of the internal carotid artery –> supplies anterior wall of the middle ear
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31
Q

√What are the 3 arch structures?

A

1.Cleft/groove (ectoderm) –> skin and epithelium
2.Arch (mesoderm) –> nerves, bone, muscles, etc.
3.Pouch (endoderm) –> mucosa, glands

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32
Q

√What are the two theories of preauricular sinus and the theory of tag formation?

A
  1. Defective or incomplete hillock fusion during auricular development
  2. Localized folding of ectoderm during auricular development is the cause of preauricular sinus formation
  3. The first 3 hillocks are most often linked to supernumerary hillocks, leading to preauricular tag formation
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33
Q

√What is the embryology of the tympanic membrane?

A

The tympanic membrane is a trilaminar structure comprising of 1st arch ectoderm (lateral epidermis), mesoderm (fibrous layer), and endoderm (medial mucosa)

Tympanic ring starts ossification in 3rd gestational month

Horizontal position initially, assumes vertical position by 3 years

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34
Q

√Describe the Embryology of the middle ear

A

4th week: A “tubotympanic recess” is formed by laterally migrating 1st arch and pouch. The terminal end of the tubotympanic recess buds into four sacci: the saccus anticus, the saccus medius, the saccus superior, and the saccus posticus. These sacci expand progressively to replace middle ear mesenchyme and mastoid mesenchyme.
5th-6th week - Mesoderm between branchial cleft and otic capsule condense to form ossicles

Endodermal pouch continues growing by surrounding the ossicles and supporting structures. The walls of the expanding sacci envelop the ossicular chain and line the walls of middle ear cavity; the interface between two sacci gives rise to several mesentery-like mucosal folds, transmitting blood vessels and ligaments to middle ear contents. It remains slit-like into the 5th month, and expands into an open space by the 8th month

Mastoid pneumatization starts in late fetal life, and the antrum present at birth

Meckel’s cartilage –> superior mesotympanum
Reichert’s cartilage –> inferior mesotympanum

90% of people with middle ear abnormalities will have external deformities

https://entokey.com/middle-ear-compartments/

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35
Q

√Describe the embryologic derivations of the malleus

A

Head, Neck, Anterior mallear ligament - Meckel’s cartilage (1st arch)

Manubrium, long process - Reinchert’s cartilage (2nd arch)

Anterior process - Process of folius - mesenchyme derivative

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36
Q

√Describe the embryologic derivatives of the incus

A

Short process and body - Meckel’s cartilage 1st arch

Long process/lenticular process - Reichert’s cartilage 2nd arch

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37
Q

√What is the embryologic development timeline of the malleus and incus?

A

6th week - single mass
8th week - Separated mass with malleo-incudal joint formed
16th week - ossification in long process of incus
17th week - ossification in medial neck of the malleus
Birth - Ossicles adult size and shape

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38
Q

√What is the most common abnormality in middle ear atresia?

A

Incudomalleolar fusion (Fusion of malleus to a bony atretic plate)

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39
Q

√Identify the structures formed from the four embryologic sacs of the middle ear

A

Main mucosal sacs of the middle ear, develop between 12th & 28th gestational weeks

Saccus Anticus - Anterior pouch of von troltsch (part of the anterior attic compartment)
Saccus Medius - Epitympanum & petrous area
Saccus Posterior/Posticus - Sinus tympani, OW & RW niches
Saccus Superior - Posterior pouch of Von Troltsch (pneumatizes squamous part of mastoid, inferior incudal space), part of the mastoid, inferior incudal space

https://entokey.com/middle-ear-compartments/

https://otosurgeryatlas.stanford.edu/otologic-surgery-atlas/cholesteatoma/growth-patterns-of-cholesteatoma/

https://otosurgeryatlas.stanford.edu/wp-content/uploads/2020/06/8a-11.jpg

https://image.slidesharecdn.com/spacesofmiddleearandtheirsurgicalimportance-161104112539/85/spaces-of-middle-ear-and-their-surgical-importance-12-320.jpg?cb=1665686024

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40
Q

√What should you do if there is a persistent stapedial artery encountered in surgery?

A

Do NOT cut it! Often repalces the middle meningeal artery

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41
Q

√Describe the embryology of the semicircular canals

A

Order of formation:
1. Superior
2. Posterior
3. Lateral

Lateral canal affected most often in congenital conditions because its last to develop

Sensory epithelium derived from ectoderm

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42
Q

Label an image of semicircular canal anatomy

A

See page 216 vancouver notes

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43
Q

√What is the dividing line between the pars flaccida and tensa?

A

Anterior and posterior mallear folds

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44
Q

√What is the dividing line between the mesotympanum and epitympanum?

A

Anterior and posterior mallear folds

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45
Q

√Describe the average size of the tympanic membrane

A

Width ~8-9mm
Height 9-10 mm
Surface area 70-80mm^2
Vibrating surface area ~55mm^2

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46
Q

√What is the tympanic sulcus?

A

The sulcus in which the annulus sits in. It is deficient superiorly thereby creating the pars flaccida

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47
Q

√What is the notch of Rivinus?

A

The superior annular defect between the anterior and posterior malleal fold - the area where fibrous annulus is missing. More likely to get a retraction pocket here.

48
Q

What is the spine of henle?

A

Suprameatal spine located immediately below the posterior root of zygomatic process, which is the projection for attachment of the auricular cartilage.

Landmark for lateral wall of the mastoid antrum.

49
Q

What are the borders of Trautmann’s triangle and what is its significance?

A

Borders:
Anterior - Bony labyrinth
Posterior: Sigmoid sinus
Superior: Superior petrosal sinus or dura

Significance:
- Weak spot for infections to enter the posterior cranial fossa
- Landmark for potential approach to posterior cranial fossa (for PCF lesions)

Dissected in the cnotext of posterior transpetrosal approaches:
- Retrolabyrinthine
- Translabyrinthine
- Transcochlear

Figure 175.6 Cummings; Page 217 Vancouver notes

50
Q

What is Donaldson’s Line?

A

DONALDSON’S LINE:
- Line used to landmark the location of the endolymphatic sac
- Defined by a line drawn parallel to the horizontal SCC and bisecting the posterior SCC

Significance:
- Divides Trautmann’s triangle into superioir and inferior compartments
- The endolymphatic sac is inferior to Donaldson’s line

Kevan Otology 72

51
Q

What is Hyrtl’s fissure?

A

A congenital abnormality - tympanomeningeal fissure - normally closes off at 24-26GA but in some patients may not close off.

A direct connection between the subarachnoid space (near the glossopharyngeal ganglion and the posterior cranial fossa behind the ganglion) and middle ear (hypotympanum inferior and anterior to the round window) that has been a reported source of CSF leak.

Reports of cochlear implants inadvertently placed here

Vancouver 217

52
Q

√Describe the blood supply to the incus and incudostapedial joint

A
  1. Vessel to the incus long process
    - Incudal artery –> from Anterior tympanic artery (From IMAX)
    - Within the mucosa and bone
  2. Vessel along the stapedius tendon
    - Fallopian canal branch of the superficial petrosal artery (Middle Meningeal/IMAX)
  3. Vessels ascending the staples crura
    - Anterior Crura: Superior tympanic artery & inferior tympanic artery
    - Posterior crura: Superficial petrosal artery branch within the fallopian canal
  4. Vessels passing via the mucosal folds, ligaments, and adhesions

Above vessels combine into a plexus surrounding the IS joint

53
Q

√What happens to the blood supply of the incus when the stapes superstructure is removed? What are the implications for stapedectomy?

A

When stapes superstructure is removed, 3/4 blood supply to the incus are removed (inferior tympani, superior tympanic, and superficial petrosal)

Need to be careful to preserve the branches of the anterior tympanic artery supplying the incus long process in order to avoid necrosis

See image page 218 Vancouver notes

54
Q

√What is the blood supply to the stapedius tendon?

A

Terminal branches of anastomosis of superficial petrosal artery (br. of Middle meningeal) and stylomastoid artery (br. of posterior auricular) supply facial nerve

Located posterior inferior from the pyramidal eminence

55
Q

√What is the blood supply to the posterior crus of the stapes?

A

Posterior crural artery (terminal branch of superficial petrosal artery)

Page 219 Vancouver

56
Q

√What is the blood supply to the anterior crus of the stapes?

A

Anterior crural artery - from anastomosis of the superior and inferior tympanic arteries

Page 219 Vancouver

57
Q

√What are the ligaments of the malleus?

A

Superior
Anterior (main)
Lateral
Tensor Tympani (V3)

SALT

58
Q

√What are the ligaments of the incus?

A

Superior
Lateral (infold)
Posterior (main)

SLP

59
Q

√What ligaments are involved in the main rotation of the ossicles?

A

Mainly around the anterior malleolar and posterior incudal ligaments.

The others maintain the meso and epitympanic folds

A + P

60
Q

√Why is the incus long process most susceptible to necrosis?

A

Single arterial blood supply (incudal artery, from anterior tympanic artery)

61
Q

√How many turns is the cochlea?

A

2.5 (2.25 cummings)

62
Q

√Define modiolus

A

The porous bony centre of the cochlea which contains acoustic nerve fibres

63
Q

√Define spiral lamina

A

Spiral bony shelf that extends from the modiolus, partially separates the upper and lower chambers into scala vestibuli and scala tympani, and serves as an attachment point for the tectorial and basilar membranes.

64
Q

√Define Reissner’s membrane

A

Separates the scala media from scala vestibuli

65
Q

√What are the 3 sections of the cochlea and what are their membranous separations?

A

Scala Vestibuli (upper)
– Reissner’s membrane separates here –
Scala Media
– Basillar membrane separates here –
Scala Tympani (lower)

66
Q

√What is the origin, cells that produce it, duct that it travels through, associated bony canal, and ionic composition including protein and glucose content of perilymph vs. endolymph?

A

Perilymph:
- Origin: CSF (positive for beta-2-transferrin)
- Produced by: choroid plexus (absorbed by arachnoid granulations)
- Duct: Perilymphatic duct
- Bony canal: Cochlear aqueduct
- Ionic composition: High Na, Low K (paucity of potassium in perilymph) - Na = 139, K = 4, Cl = 0, Protein = 200-400, GLucose = serum concentration

Endolymph:
- Origin: Endolymphatic sac
- Produced by: Stria vascularis (cochlear), dark cells of macular and crista (utricle, saccule of SCCs)
- Duct: Endolymphatic duct
- Bony canal: Vestibular aqueduct
- Ionic composition: High K, Low Na - Na 13, K 144, Cl 120, Protein 126, Glucose low

67
Q

√What is the difference between the bony osseous vs. membranous labyrinth?

A

Bony labyrinth - within the petrous portion of the temporal bone, the hardest bone in the body, which encases the inner ear.

Membranous labyrinth - membraneous portion housing endolymph within the bony labyrinth

68
Q

√Define helicotrema

A

Apex of the cochlea where fluid-filled scala chambers connect and communicate, contained within the bony labyrinth

69
Q

√Label all the parts of the Organ of Corti

A

See Nadia and Kevan’s notes

70
Q

√Define crista and macula

A

Crista: sensory neuroepithelium within the ampulla (bullous base of each SCC) of the SCCs

Macula: Sensory neuroepithelium of the otolithic organs (saccule - closer to cochlea; and utricle - closer to SCC)

71
Q

√Define Impedence

A

Resistance to movement

Ratio between the sound pressure applied and the change in velocity of a volume - amount of sound pressure needed to produce a unit change in a volume’s velocity

E.g. water has a higher impedance than air

72
Q

√Define Impedence matching

A

How the middle ear amplifies acoustic energy to help overcome the impedance mistach between the air (external ear) and fluid (inner ear)

ie. increasing the sound pressure applied ratio to move the same velocity through the different volume

73
Q

√What are the resonant frequencies of the following external and middle ear

Pinna
EAC
TM
Ossicular chain
Middle ear

A

Pinna 5000 Hz
EAC 2500 Hz (3000)
TM 1200 Hz (800-1600)
Ossicular chain 600 (500-2000)
Middle ear 800 Hz

74
Q

√Describe how sound amplification occurs across the TM for impedence matching

A

Area Ratio:
- Ratio between surface area of the TM and surface area of footplate is ~20. Sound is amplified by 20log (20) = ~26dB

Lever ratio:
- Manubrium of the malleus is longer than the long process of the incus by about 1.3 times. Sound is amplified 20log(1.3) = 2.3dB

Total amplification is therefore around 28-30dB which helps overcome the impedence mismatch transitiong from air to fluid

75
Q

√What is the equation used to calculate the sound amplification?

A

dB = 20log (1) J/Jr
J= sound intensity
Jr = intensity of reference sound

Sound pressure measured in pasclas is proportional to the square root of sound intensity

dB = 10log10 P^2/Pr^2 = 10log10 (P/Pr)^2 = 20log10 P/Pr

76
Q

√Describe the 3 lever principles of impedance matching by the middle ear to accomplish the required pressure transformation (Hermann von Helmholtz definition). What is the overal SPL gain?

A

Hydraulic lever: Surface area differences between TM (55mmsquared) and footplate at oval window (3.2mmsquared) 20.8:1 (Area ratio)

Ossicular lever: Difference in relative lengths between manubrium and long process of incus 1.3:1 (lever ratio)

Caternary lever: Due to the concave curved shaped of the TM and radial fibers, when stretched it amplifies towards the attachment/umbo, leading to 2x amplification of sound towards umbo

Overall SPL gain ~25-30dB at 1kHz

77
Q

√What are three factors that impact acoustic impedence?

A
  1. Stiffness
  2. Resistance (damping)
  3. Mass

Acoustic impedence increases in proportion to these factors

78
Q

√Define Acoustic coupling

A

When a sound stimulus strikes the cochlear windows directly, most of the acoustic energy is deflected. The pathway of direct transmission is called acoustic coupling (vs. ossicular coupling via ossicles)

This is the primary method of sound transmission to the cochlear in the event of ossicular discontinuity with maximal CHL.

79
Q

What is the difference in sound level between ossicular coupling and acoustic coupling? Ie. what hearing loss amount would be expected in patients with complete ossicular discontinuity?

A

60dB

80
Q

√List 4 methods that binaural hearing improves auditory perception

A
  1. Sound Localization (superior olive and inferior colliculus)
  2. Overcomes head shadow effect (region of reduced amplitude of a sound because it is obstructed by the head)
  3. Binaural summation (louder - sounds heard equally in both ears are centrally amplified)
  4. Binaural squelch (sounds heard only in 1 ear are centrally diminished. This together with binaural summation allow for hearing within noise)
81
Q

√Define Resonance

A

Resonance occurs where the stiffness and impedence components of acoustic impedence cancel each other out (ie. at the minima)

Stiffness varies inversely with frequency (dominant at low frequencies)

Impedence of a mass increases with higher frequency (dominant at high frequency; ie. impedence is high with high frequency and low with low frequency)

82
Q

Define admittance

A

Describes the volume of velocity required to produce a unit of sound pressure (inverse of impedence)

83
Q

√Define acoustic immittance

A

Term that groups both impedence and its inverse, admittance

84
Q

√What is the blood supply to the inner ear?

A
  1. Labyrinthine artery
    - Branches off of AICA (80%), Superior cerebellar artery (24%) or Basilar artery (16%)
    - Splits into anterior vestibular and common cochlear arterys

Anterior vestibular artery
- Supplies utricle & part of saccule, horizontal and anterior SCC

Common cochlear artery
- Splits into
- 1) Proper cochlear artery/spiral modiolar artery –> supples cochlea except basal turn
- 2) Vestibulocochlear artery –> Further splits into
- a) Cochlear ramus artery (supplies basal turn of cochlea)
- b) posterior vestibular artery (supplies posterior SCC, saccule)

85
Q

Describe briefly the path of a soundwave from the external ear to the acoustic nerve

A

1) EAC –> TM –> Ossicular lever –> stapes footplate –> oval window
2) Fluid wave propagates through the cochlea and across the scala vestibuli–>media–>tympani out through the round window
3) Lower frequency sounds travel further through fluid (impedence of a mass decreases with lower frequencies) and go further up the cochlear towards the helicotrema
4) Deflections of the tectorial membrane with respect to the basilar membrane (that Organ of Corti sits on) causes hair cell depolarization
5) Hair cell depolarization –> spiral ganglion in modiolus –> cochlear nerve

86
Q

√What separates the oval window and round window

A

Cochlear duct aka. Scala media

87
Q

√Which scala corresponds to which cochlear window?

A

Vestibuli = oval
Tympani = round

Page 219 Vancounver notes photos

88
Q

√Label all the parts of the membranous labyrinth

A

See Vancouver page 219

89
Q

√What are the molecular functions of the inner and outer hair cells

A

Inner hair cell: Opens voltage gated calcium channels and activates the auditory nerve
Outer hair cell: Changes length depending on depolarization or repolarization via protein ‘prestin’, which adds energy to the basilar membrane depending on mechnical feedback - allows for amplification and fine tuning of sound/vibrations within the cochlea

90
Q

√What is a persistent stapedial artery

A

A branch off the ICA that gives the normal stirrup shape of the stapes in utero but regresses at 7th week GA; failure of regression = persistent stapedial artery

See Kevan’s notes page 8 image

91
Q

√Describe the course of a persistent stapedial artery

A

Arises from the internal carotid artery, enters the hypotympanum, goes through the obturator foramen (of stapes), goes parallel along the tympanic segment of the facial nerve past the geniculate ganglion, then enters dura of the middle cranial fossa as the middle meningeal artery

Page 221 Vancouver

92
Q

√Describe 4 radiologic findings of a persistent stapedial artery

A
  1. Absent middle meningeal artery and absent foramen spinosum (where the artery enters in the middle cranial fossa through the greater wing of sphenoid)
  2. Enlarged tympanic facial nerve canal (combination of facial nerve and parallel running persistent stapedial artery)
  3. Enhancing hypotympanic mass
  4. Dehiscent/aberrant ICA
93
Q

√What other vascular “anomaly” is often associated with a persistent stapedial artery?

A
  1. Aberrant ICA
  2. Middle meningeal artery may arise off of the persistent stapedial artery instead of the IMAX (or be absent)
94
Q

List 7 differential of a soft tissue mass overlying the promontory

A

Glomus tumor
Cholesteatoma
Persistent stapedial artery
High riding jugular bulb
Encephalocele
Aberrant carotid artery
Dehiscent facial nerve

“GCS HEAD”

95
Q

√Pathophysiology and Course of an Aberrant Internal Carotid Artery

A
  1. Cervical portion if the ICA fails to develop
  2. Inferior tympanic artery (branch from the ascending pharyngeal) enters the middle ear through inferior tympanic canaliculus, and joins the caroticotympanic artery and forms a horizontal petrous portion of the ICA

Commonly associated with persistent stapedial artery

https://www.neuroangio.org/wp-content/uploads/AP/AP_Aberrant_Carotid_Schema_Radiographics.jpg

96
Q

Imaging of the Temporal Bone:

  1. Vessel below the cochlea
  2. Vessel below the vestibule
  3. Carotid and Jugular bulb - which is anterior vs. posterior on axial scan?
  4. Vessel seen on the same slice as the TMJ
  5. How do you find the subarcuate artery?
  6. What is in the same plane as the ossicles?
  7. How do you find the Cochlear aqueduct?
  8. What are seen at the same level of the oval window?
  9. What can be confused with the tensor tympani?
  10. What needs to always be assessed on a TB scan?
A
  1. Carotid
  2. Vein (jugular bulb)
  3. Carotid is anterior, vein posterior
  4. Carotid
  5. Runs parallel to the IAC, runs under the superior SCC
  6. Horizontal SCC
  7. Parallel and slightly below the IAC
  8. Sinus tympani, pyramidal eminence, facial recess
  9. Facial nerve (muscle is higher)
  10. Degree of aeration, dura, facial nerve, vessels, labyrinth integrity, extent of disease
97
Q

What runs through the petromastoid suture

A

Petromastoid suture (aka. subarcuate canaliculus) - subarcuate artery

98
Q

What runs through the petrotympanic fissure

A

Petrotympanic fissure - exit of chorda tympani

99
Q

What runs through the superior tympanic canaliculis 2

A

Superior tympanic canaliculus - superior tympanic artery, LSPN

100
Q

What runs through the hiatus of facial canal 1

A

Hiatus of facial canal - GSPN from geniculate gangion to exit middle cranial fossa

101
Q

What runs through the singular canal 1

A

Singular canal - IAC to posterior SCC/vestibule junction - singular nerve (posterior ampullary nerve, branch of inferior vestibular nerve)

102
Q

What runs through the vestibular aqueduct

A

Vestibular aqueduct - vestibule to posterior petrous bone (contains endolymphatic duct and connects to endolymphatic sac)

103
Q

What runs through the cochlear aqueduct

A

Cochlear aqueduct - subarachnoid space to basal turn (contains perilymphatic duct)

104
Q

What is the ductus reuniens

A

Ductus Reuniens - saccule to cochlear duct

105
Q

What runs through the inferior tympanic canalicus

A

Inferior tympanic canaliculus - jacobsen’s nerve enters here and exits at hiatus for LSPN

106
Q

What runs through the mastoid canaliculus and tympanomastoid fissure?

A

Mastoid canaliculus and tympanomastoid fissure - entry and exit point for Arnold’s nerve

107
Q

What runs through the canal of huguier? 3

A

Canal of Huguier to petrotympanic fissure - anterior tympanic artery, anterior tympanic ligament, exit point of chorda tympani

108
Q

Where does Jacobsen’s nerve enter and exit? Where does Arnold’s nerve enter and exit?

A

Jacobsen’s nerve (tympanic branch of glossopharyngeal nerve - radiates pain from oropharyngeal lesions): enters inferior tympanic canaliculus (Jacobsen’s canal) with inferior tympanic artery, and exits at the hiatus for LSPN

Arnold’s nerve (auricular branch of the vagus nerve - makes you cough with ear cleaning): enters mastoid canaliculus and exits tympanomastoid fissure

See Vancouver notes 221

109
Q

Where does the chorda tympani enter and exit in the temporal bone?

A

Enters IAC with facial nerve to chordae posterior, exits the canal of huguier to petrotympanic fissure

110
Q

Endoscopic anatomy of the middle ear - label structures

A

See Vancouver notes 222

Look at as many photos as possible!

111
Q

What are the acoustic properties of the head that assist in sound localization? 3

A
  1. Head Shadow effect: head attenuates sound waves with wavelengths shorter than the width of the head (>2kHz) by 5-15dB
  2. Interaural time difference: Maximum ~0.6msec time difference for sound hitting one ear to reach the other ear
  3. Head-related transfer function (spectral acoustic characteristics of sound): The pinna and head affect the intensities of frequencies. Spectra of intensities of sound is changed by the head and the pinna based on the location of sound. Brain is able to use these spectral cues to infer the location
112
Q

√How many rows of outer hair cells vs. inner hair cells? Which are more important and why?

A

Inner hair cells: 1 row, 3500, flask shaped, few
- 90% of neurons innervating the cochlear synapse on the inner hair cells (Type 1 neurons, bipolar, myelinated), ~20 neurons synapse on each IHC

Outer hair cells: 3 rows, 12000, cylindrical, many
- 10% of neurons innervating the cochlea synapse on the OHC (type 2 neurons, pseudomonopolar, unmyelinated), 1 neuron innervates ~10OHCs

2000 efferent neurons from superior olive synapse on the hair cells (LSO to IHC, MSO to OHC)

There are no kinocilia on hair cells

113
Q

√Difference between ossicular stiffness and mass. How do they affect hearing

A

Resonance frequency of the middle ear ossicles is 500-2000Hz
Changes in ossicular stiffness/mobility affect low frequency sound transmission

Changes in ossicular mass affect high frequency sound transmission (harder to vibrate the system)

In otosclerosis, early lesions decrease the overall mobility (increases stiffness) of the ossicular chain, and subsequently will affect the ossicular mass (hearing loss will spread from low into the higher frequency)

114
Q

√What is Tonotopic organization?

A

Organ of corti is ~35mm long from base to apex. Travelling wave from middle ear causes simultaneous fluid wave in the perilymph (oval window footplate > scala vestibuli > apex helicotrema > scala tympani > round window)
Each place on the basilar membrane responds best to a specific frequency.

Higher F sounds cause maximal displacement of the basilar membrane in the basal region.

Low F soudns cause maximal displacement of the basilar membrane in the apex

Tonotopic organization preserved in high brainstem nuclei

115
Q

√What is the primary auditory cortex?

A
  • Resides in the temporal lobe, close to the sylvian fissure
  • The two major centres for auditory processing here are the primary auditory cortex (area A1) and the auditory association cortex (area A2)

A1 = Brodmann area 41
A2 = Brodmann area 22 and 42

116
Q

√Describe the pathway of acoustic energy input from spinal ganglion to cortex (auditory cortex)? What is the efferent system?

A

ECOLI MC (Afferent system):
1. Eighth nerve (cochlear nerve)
2. Cochlear nucleus
3. Superior olivary complex (first to receive binaural input, plays role in sound localization)
4. Lateral lemniscus
5. Inferior colliculus (first area to integrate information from both auditory and non-auditory sources)
6. Medial geniculate body in thalamus
7. Cortex (Heschl’s gyrus, primary auditory cortex) in temporal lobe

Efferent system out of brain to cochlea:
1. Originates from olivocochlear bundle, which arises from the medial superior olive and lateral superior olive
2. Travels with inferior division of vestibular nerve
3. Pass through saccular ganglion and enter spiral ganglion via vestibulocochlear anastomosis of Oort
4. Provide direct innervation of OHC and indirect modulation of IHC

117
Q

Describe the Embryology of the Inner Ear

A

Kevan’s notes last few pages

Otology & Neurotology (17 decks)

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