oto Overview

Question 1

Describe the sensory innervation of the pinna and

external auditory canal (EAC).

Answer 1

Sensation of the auricle is provided by the greater auricular
and lesser occipital nerve (from the cervical plexus), as well
as small sensory branches of the facial nerve and
auriculotemporal nerve. The EAC is supplied by overlapping
contributions from cranial nerves (CN) V, VII, IX, and X.

Question 2

What is the foramen of Huschke?

Answer 2

The foramen of Huschke is a developmental defect resulting
from incomplete fusion of the greater and lesser tympanic
spines. When present, it creates a connection between the
EAC and the parotid gland, glenoid fossa or infratemporal
fossa.

Question 3

What are the fissures of Santorini?

Answer 3

The fissures of Santorini are anatomical communications
that allow lymphatic movement between the anterior
cartilaginous EAC and the parotid gland and glenoid fossa.

Question 4

What is the notch of Rivinus?

Answer 4

The notch of Rivinus is the deficient portion of the tympanic
annulus where the pars flaccida attaches to the squamous
portion of the temporal bone.

Question 5

How are the pars flaccida and pars tensa of the

tympanic membrane structurally different?

Answer 5

The pars flaccida is, as its name implies, more compliant
than the pars tensa. The pars tensa is slightly thicker and
contains a middle fibrous layer in addition to an outer skin
layer and inner mucosal layer.

Question 6

The tympanic membrane is formed by what
embryonic layer(s)?

Answer 6

The outer epidermal layer from the first branchial cleft
(ectodermal origin); middle fibrous layer from neural crest
mesenchyme (mesodermal origin); inner mucosal layer
from the first pharyngeal pouch (endodermal origin)

Question 7

Where does the carotid artery lie in relation to the

eustachian tube?

Answer 7

The carotid artery courses just medial to the more anterior

cartilaginous portion of the eustachian tube.

Question 8

In patients with cleft palate, dysfunction of which
muscle is most strongly implicated in causing
recurrent otitis media?

Answer 8

Tensor veli palatini

Question 9

What is the most common intratemporal location

of facial nerve dehiscence?

Answer 9

It occurs most commonly near the oval window, second

most commonly at the second genu.

Question 10

Describe the origin, insertion, and action of the

tensor tympani muscle.

Answer 10

The tensor tympani originates from the greater wing of the
sphenoid, cartilage of the eustachian tube, and the walls of
the semicanal of the tensor tympani. Its tendon then wraps
around the cochleariform process to insert onto the medial
aspect of the neck and manubrium of the malleus. It
functions to medialize the tympanic membrane and
increase the impedance of the ossicular chain.

Question 11

What landmarks may be used to help identify the

facial nerve during middle ear surgery?

Answer 11

The Jacobson nerve, located on the cochlear promontory,
can be followed superiorly to the cochleariform process.
The facial nerve is immediately medial and superior to the
cochleariform process and tensor tympani. The facial nerve
can also be identified immediately superior to the oval
window.

Question 12

Aside from the muscles of facial expression, what

muscles does the facial nerve innervate?

Answer 12

In addition to the muscles of facial expression, the facial
nerve innervates all the other muscles of the second
branchial arch, specifically, the stapedius muscle, the
stylohyoid, and the posterior belly of the digastric.

Question 13

What is the cog?

Answer 13

The cog is a coronally oriented bony septum located just
anterior to the head of the malleus that seperates the
anterior epitympanic recess (supratubal recess) from the
attic.

Question 14

When looking at the external surface of the
mastoid cortex, what landmark can be used to
approximate the level of the middle cranial fossa?

Answer 14

The temporal line, which represents the inferior insertion

point of the temporalis muscle, can be used as a landmark.

Question 15

Describe the boundaries of the Macewen triangle

suprameatal

Answer 15

The suprameatal crest, posterior margin of the external
auditory canal, and the tangential line from the posterior
ear canal bisecting the suprameatal crest are the bounda-
ries of the Macewen triangle, which approximates the
antrum.

Question 16

What is the Körner septum?

Answer 16

The Körner septum is a bony plate dividing the mastoid air
cells superficial to the antrum. Embryologically, it is the
junction between the petrous and squamous portions of
the temporal bone and creates a “false bottom” during
mastoidectomy.

Question 17

Which cells are primarily responsible for trans-

ducing acoustic energy into neural signals?

Answer 17

Inner hair cells are the primary cells onto which afferent
auditory neurons (spiral ganglion cells) synapse. The outer
hair cells also contribute to transformation of acoustic
energy into neural signal; however, they primarily play a role
in “tuning” the cochlea to improve frequency selectivity and
sensitivity.

Question 18

What are the boundaries of the scala media?

Answer 18

In the cross-section of the cochlea, the scala media is separated from the scala vestibuli by the Reissner membrane. The basilar membrane and osseous spiral lamina separate the scala media and scala tympani. The boundaries of the outer periphery of the scala media are the stria vascularis and the spiral ligament.

Question 19

What two structures are connected by the peril-

ymphatic (periotic) duct?

Answer 19

The perilymphatic duct, which runs in the bony canal of the
cochlear aqueduct, connects the scala tympani of the
cochlea and the subarachnoid space of the posterior cranial
fossa.

Question 20

Which structures are innervated by the superior

and inferior vestibular nerves, respectively?

Answer 20

Superior vestibular nerve innervates the superior and lateral semicircular canals and the utricle. Inferior vestibular nerve innervates the posterior semicircular canal, and the saccule.

Question 21

Where is the primary auditory cortex located?

Answer 21

Brodmann areas 41 and 42 of the upper temporal lobe

Question 22

Describe the geometric anatomy of the semi-

circular canals and the physiologic significance of this arrangement.

Answer 22

The three semicircular canals are located in three mutually perpendicular planes. This orientation provides the vestibular system with independent resolution of rotational movements in three different axes (pitch, roll, and yaw).

Question 23

Describe the course and functions provided by the

nervus intermedius.

Answer 23

The taste, secretory, and sensory fibers of the facial nerve are carried by the nervus intermedius. It exists as a distinct nerve in the cerebellopontine angle (CPA) and internal auditory canal (IAC), but on entering the meatal foramen, these fibers exist within the body of the facial nerve.

Question 24

What cell bodies are located in the geniculate

ganglion?

Answer 24

Cell bodies of the special sensory taste neurons carried by the chorda tympani nerve

Question 25

What nerve fibers are carried by the greater superficial petrosal nerve?

Answer 25

Preganglionic parasympathetic fibers that synapse in the
pterygopalatine ganglion, as well as afferent special sensory
taste fibers that supply the soft palate

Question 26

What percentage of temporal bone specimens demonstrate dehiscence of the geniculate ganglion on the floor of the middle fossa?

Answer 26

16%

Question 27

What is the prevalence of internal carotid artery

dehiscence at the floor of the middle cranial fossa?

Answer 27

Approximately 20%

Question 28

Describe the boundaries of the Glasscock triangle

posterolateral

Answer 28

Greater superficial petrosal nerve, V3, line connecting

foramen spinosum and arcuate eminence

Question 29

Describe the boundaries of Kawase triangle

posteromedial

Answer 29

V3, greater superficial petrosal nerve, arcuate eminence, superior petrosal sinus. It marks the boundaries of anterior
petrosectomy for gaining access to the posterior fossa.

Question 30

What extratemporal branches of the facial nerve

arborize proximal to the pes anserinus?

Answer 30

The postauricular nerve, nerve to the stylohyoid, and nerve to the posterior belly of the digastric muscle

Question 31

The external ear is formed by what mesodermal

structures?

Answer 31

The six hillocks of His:
● First Arch
1: Tragus
2: Helical crus
3: Helix
● Second Arch
4: Antihelix
5: Antitragus
6: Lobule

Question 32

Incomplete fusion or supernumerary development

of the hillocks of His may lead to what conditions?

Answer 32

Preauricular cysts, pits, or tags

Question 33

Describe the embryologic basis of a persistent

stapedial artery.

Answer 33

The stapedial artery is derived from the second branchial
arch. This is normally a transient structure, but in rare
instances, it can persist into adulthood.

Question 34

What skull base abnormality is classically seen with a persistent stapedial artery?

Answer 34

Lack of an ipsilateral foramen spinosum

Question 35

Describe the embryologic origin(s) of the ossicles.

Answer 35

The head and neck of the malleus, as well as the incus body
and short process, are derived from the first branchial arch
(Meckel cartilage). The manubrium of the malleus, long
process and lenticular process of the incus, and the stapes
superstructure are derived from the second branchial arch
(Reichert cartilage). The vestibular half of the stapes
footplate and annular ligmanent are thought by many
authorities to be derived from the otic capsule.

Question 36

From which germ cell layers and branchial arch(es)

does the otocyst arise?

Answer 36

First seen at the end of the 3rd week of development, the
otic placode is a thickening of the ecdodermal surface of the first branchial groove. This invaginates into the under-
lying mesoderm, which it eventually becomes surrounded by to form the otocyst. This structure goes on to develop
into the otic labyrinth.

Question 37

List the primary acoustic functions of the external

ear.

Answer 37

● Filter to reduce low-frequency background noise
● Resonator to amplify mid frequency sounds (up to 20 dB)
● Direction-dependent filter to augment spatial perception
at high frequencies

Question 38

Compared with adults, what anatomical charac-
teristics of the eustachian tube in young children
predisposes toward development of acute otitis
media?

Answer 38

The eustachian tube is narrower, shorter, and oriented
more in a horizontal plane in children, putting the middle
ear at a higher risk for exposure to nasopharyngeal
secretions and poor aeration.

Question 39

Describe the acoustic transformer mechanism of

the middle ear.

Answer 39

The three “levers” provide an average gain of 20 to 30 dB:
● Catenary lever: Elastic properties of stretched tympanic
membrane fibers directing sound to the centralized
malleus
● Ossicular lever: The length of the manubrium of the
malleus divided by the length of the long process of the
incus (1:3 ratio)
● Hydraulic lever: A 22:1 ratio of the tympanic membrane to
the oval window

Question 40

Describe the electrolyte composition of the

cochlear fluids.

Answer 40

Perilymph located in scala vestibul and scala tympani is
similar to serum and cerebrospinal fluid (CSF) in electrolyte
composition (high Na and low K concentration). Endolymph
is located within the scala media and is similar to
intracellular fluid in electrolyte composition (low Na and
high K concentration).

Question 41

How are movements of the oval window (stapes
footplate) and the round window membrane
related?

Answer 41

They are out of phase by 180 degrees. In other words,
motion at the oval window into the vestibule leads to an
outward movement of the round window membrane into
the middle ear. If pressure is exerted on both the round
window and oval window simultaneously and equally, phase
cancellation occurs resulting in significant hearing loss.

Question 42

Describe the tonotopic organization of the coch-

lea.

Answer 42

The cochlea (specifically the basilar membrane) is tono-
topically “tuned,” such that the high frequency sounds are most effectively transduced at the basal cochlea, whereas
low-frequency sounds are best transduced in the apical
segments.

Question 43

What effects do ampullopedal and ampullofugal
displacement of the semicircular canal kinocilia
have on the firing rates of the vestibular nerves?

Answer 43

Ampullopetal (toward the vestibule) displacement of the
kinocilia of the horizontal canal and ampullofugal (away
from the vestibule) displacement of the kinocilia of the
superior and posterior canals increase vestibular nerve firing
rates.