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What embryological structures is the auricle developed from?
The hillocks of His
How many hillocks are there and which branchial arches do they arise from?
- 1-3 arise from the first branchial arch
- 4-6 arise from the second branchial arch
What does each hillock of His become?
- 1 - tragus
- 2 - helical crus
- 3 - helix
- 4 - antihelix
- 5 - antitragus
- 6 - lobule and lower helix
How does a preauricular sinus tract form?
From improper fusion of the 1st and 2nd branchial arches
When does development of the external auditory canal (EAC) begin?
The canal begins to develop at 28 weeks gestation.
At what month(s) gestation does the ear canal open?
At what age does the EAS reach adult size?
What is the significance of a congenitally malformed auricle?
The auricle develops early, making malformations of the middle ear, mastoid, and VII more likely.
What is the significance of a normal auricle with canal atresia?
The EAC begins formation late (28th week), so the middle ear and ossicles are more likely to be normal.
Which ossicles develop from the first branchial arch (Meckel's cartilage)?
- Head and neck of the malleus
- Body and short process of the incus
Which ossicles develop from the second branchial arch (Reichert's cartilage)?
- Manubrium of the malleus
- Long process of the incus
- Stapes (except footplate)
What does the stapes footplate develop from?
Which ossicular component develops from membranous bone?
Anterior process of the malleus
Which ossicular components never completely ossify?
- Part of the manubrium
- The vestibular portion of the stapes footplate
When do the ossicles reach adult size and shape?
- Adult size - at the 16th week gestation
- Adult shaped - by birth
Why is the development of the bony otic capsule unique?
- It is formed from 14 centers of ossification that fuse and leave no suture lines
- The centers are formed from cartilage, but retain no areas of chondral growth
- The bone retains its fetal character, with Haversian canals
When does the otic capsule begin formation?
- The precursors of the otic capsule are present at 8 weeks
- The ossification centers are present at 15 weeks
When does the otic capsule finish developing?
Reaches adult size by 21-24 weeks
What is the last part of the otic capsule to ossify?
Fissula ante fenestrum
When does the fallopian canal begin developing?
- 5th week gestation
- Development is not complete until several years after birth
What is the last structure of the inner ear to develop?
What does the eustachian tube (ET) develop from?
From the 1st pouch (between the 2nd arch and the pharynx)
Which branchial arch does the tensor tympani muscle arise from?
First branchial arch
True/False: The tympanic membrane is derived from ectoderm.
False; it is derived from ectoderm, mesoderm, and endoderm
At what age is the mastoid process completely pneumatized?
What is the sensory innervation of the auricle?
- Greater auricular nerve (C3)
- Auriculotemporal nerve (V3)
- Lesser occipital nerve (C2,3)
- Auricular branch of the vagus (Arnold's nerve)
- Sensory branches of VII and IX
What is Arnold's nerve?
Auricular branch of the vagus that innervates skin of the external auditory canal and auricle
What is the foramen of Huschke?
An embryologic remnant that normally obliterates in the anteroinferior portion of the medial bony EAC
What is the clinical significance of the foramen of Huschke?
Serves as a potential route for spread of tumor from the parotid gland to the temporal bone.
Which wall of the EAC is shorter - the anteroinferior or posterosuperior?
Posteriosuperior - ~25mm (vs anteroinferior - ~31mm)
How much of the EAC is cartilaginous?
How much of the ET is cartilaginous?
Where is the tympanic notch of Rivinus?
Superior portion of the tympanic ring (squamous portion of the temporal bone)
How does the composition of gas in the middle ear differ from that of room air?
Lower oxygen level and higher carbon dioxide & nitrogen levels.
What are the layers of the tympanic membrane?
- Squamous epithelium
- Radiating fibrous layer
- Circumferential fibrous layer
Which has greater sensory innervation - pars tensa or pars flaccida?
What are the three nerves of the tympanic plexus?
Which part of the ossicular chain has the most tenuous blood supply and is most prone to necrosis?
Long process of the incus
Which part of the malleus articulates with the incus?
Where in the ossicular chain does the tensor tympani muscle insert?
Manubrium of the malleus
Which part of the malleus does the anterior ligament attach to?
The neck, near the anterior process
What ligament supports the stapes?
Where does most of the movement of the stapes occur?
Anterior-superior portion of the footplate
Where in the ossicular chain does the stapedius muscle insert?
Posterior neck of the stapes
What is the scutum?
Lateral wall of the epitympanum
What are the boundaries of the epitympanum?
- Superiorly - the tegmen
- Inferiorly - the fossa incudis
- Anteriorly - the zygomatic arch
- Posteriorly - the aditus
- Medially - the lateral semicircular canal & VII
- Laterally - the scutum
Which ossicles can be found in the epitympanic recess?
- Head of the malleus
- Body & short process of the incus
What is the inferior boundary of they tympanic cavity?
What structures are anterior to the tympanic cavity?
- Carotid artery
- Canal for the tensor tympani muscle
What structures are posterior to the tympanic cavity?
- Posterior sinus
- Chorda tympani
- Fossa incudis
- Pyramidal prominence
- Stapedial tendon
What is the promontory?
Elevation of the medial wall of the tympanic cavity formed by the basal turn of the cochlea
Which 3 cranial nerves are found beneath the floor of the middle ear cavity?
- IX - glossopharyngeal
- X - vagus
- XI - accessory
Below is a diagram of the right middle ear showing its relationship with the inner ear. Name the structures:
- A - facial nerve
- B - Ponticulus
- C - Subiculum
- D - Geniculate ganglion
What structure is located inferior to the subiculum and posteroinferior to the promontory?
What structure lies between the subiculum and the ponticulus?
What structure lies superior to the ponticulus?
What structure lies between the prominence of SCC and the promontory/oval window?
Prominence of the facial canal
The following diagram is of a right middle ear viewed from below. Name the structures:
- A - facial recess
- B - facial nerve
- C - Sinus tympani
What is the most anterior structure of the medial wall of the tympanic cavity?
Cochleariform process: tensor tympani:: pyramidal process: ?
What structure is situated just medial to the tip of the cochleariform process?
Geniculate ganglion of the facial nerve.
Between which ossicles does the chorda tympani run?
Manubrium of the malleus and the long process of the incus
What is the function of the chorda tympani nerve?
- Parasympathetic innervation to the submandibular and sublingual glands
- Taste to the anterior 2/3 of the tongue
Which planes are the oval and round windows oriented in?
- Oval window is in the sagittal plane
- Round window is in the transverse plane
What structure ends blindly at the round window?
Scala tympani (lower compartment of the cochlea)
What is the name of the central bony core of the cochlea through which nerves and vessels travel?
What is the name of the area of communication between the scala vestibuli and the scala tympani?
What fluid surrounds the membranous labyrinth?
How does perilymph differ from endolymph?
- pH 7.2
- High in sodium
- Low in potassium
- Does not contain chloride
- pH 7.5
- Low in sodium
- High in potassium and chloride
True/False: The membranous labyrinth is a self-contained system.
What are the main structures of the vestibular portion of the membranous labyrinth?
Which of the main structures of the vestibular portion of the membranous labyrinth receives the crura from the three SCCs?
What structures house the crista?
What is the blood supply to the inner ear?
- Labyrinthine artery
- (branch of the anterior inferior cerebellar artery)
What structure produces endolymph?
Where does most of the resorption of endolymph occur?
What does the vestibular aqueduct carry?
- Endolymphatic duct
- Accompanying vein
Where is the primary auditory cortex?
Brodmann's area 41 in the superficial portion of the temporal bone
Which part of the vestibular labyrinth detects angular acceleration?
What do the utricle and saccule detect?
Where are cupula found?
What 3 systems determine balance?
- Vestibulo-ocular (visual)
- Vestibulo-spinal (proprioceptive)
Which part of the cochlea represents high-frequency sounds?
The basal end
What range of frequencies can the human ear detect?
- 20 - 20,000 Hz
- (the greatest sensitivity is from 500 - 3000 Hz)
What noise level begins to cause pain?
How many times louder is 60 dB than 0 dB?
What are normal ear volumes in children and adults?
- Children: 0.5 - 1.0 cm3
- Adults: 0.6 - 2.0 cm3
Which cells omit otoacoustic emissions (OAEs)?
Outer hair cells
What percentage of normal ears emit spontaneous OAEs?
35 - 60%
What are the 4 parts of the temporal bone?
What are the 4 openings into the temporal bone?
- Internal Auditory Canal (IAC)
- Vestibular aqueduct
- Cochlear aqueduct
- Subarcuate fossa
What is Hyrtl's fissure?
Connection between the subarachnoid space near the IX ganglion and the hypotympanum that allows middle ear infections to spread to the brain (normally closes with maturation)
What proportion of the population has a pneumatized petrous pyramid?
What is Trautmann's triangle?
Triangle between the external prominence of the lateral and posterior SCCs and the posterosuperior corner of the mastoid
What is Korner's septum?
- AKA the "false bottom"
- It represents the suture line between the petrous and squamous portions of the temporal bone
What is meant by a "diploic mastoid"?
Occupied by bone marrow instead of air cells
What structure forms the arcuate eminence?
True/False: The position of the cochlear duct is always inferior to the lowest border of the stapes footplate.
Besides muscles of facial expression, what muscles does the facial nerve innervate?
- Posterior belly of the digastric
- Stapedius muscle
What does the facial nerve provide general sensation for?
- Part of the auricular concha
- External auditory canal
- Tympanic membrane
What is the function of the special visceral afferent fibers of the facial nerve?
To provide taste to the anterior 2/3 of the tongue and palate (via the chorda tympani)
Where are the cell bodies for the special visceral afferent fibers of the facial nerve?
What is the function of the nervus intermedius?
- To carry visceral motor fibers to the lacrimal gland, minor salivary glands, and mucosal glands of the palate and nose (via the greater superficial petrosal nerve)
- To carry general sensory fibers from the auricular concha and external auditory canal
What are the six segments of the facial nerve?
- Internal auditory canal
Where in the brainstem is the facial motor nucleus?
Where does the facial nerve leave the brainstem?
Pontomedullary junction, close to the vestibulocochlear nerve
What are the limits of the tympanic segment of VII?
Geniculate ganglion to the 2nd genu (adjacent to the pyramidal process)
What are the limits of the mastoid segment of VII?
Pyramidal process to the stylomastoid foramen
Which segment of VII is the shortest?
Which segment of VII has the narrowest passageway?
What portion of the facial nerve is closest to the cochlea?
What 3 branches of the facial nerve are given off in its course through the temporal bone?
- Greater superficial petrosal nerve
- Nerve to the stapedius muscle
- Chorda tympani
What is the first branch of the facial nerve?
Greater superficial petrosal nerve
Where along the course of the facial nerve does this nerve branch off?
What is the blood supply to the geniculate ganglion?
- Greater superficial petrosal artery
- (branch of the middle meningeal artery)
What is the function of the greater superficial petrosal nerve?
- Salivation from minor salivary glands
- Mucosal secretions from nose and palate
Where do the preganglionic parasympathetic neurons of the greater superficial petrosal nerve synapse?
Branches of which nerve then carry the postganglionic parasympathetic neurons to the mucus-secreting glands in the nose, sinuses, and palate?
Maxillary division of the trigeminal nerve
What is the facial hiatus?
Dehiscence of variable size in the petrous portion of the temporal bone in the floor of the middle cranial fossa, which marks the entrance of the greater superficial petrosal nerve into the middle cranial fossa
How is the facial hiatus clinically significant?
The geniculate ganglion usually lies deep to the hiatus but in 5-10% of patients, it lies under the dura within the hiatus and without a bony covering
Describe the path of the facial nerve in the temporal bone:
Enters the IAC --> travels laterally for a short distance --> just superior to the promontory it makes a sharp turn to run posteriorly (at the external/first genu and the geniculate ganglion) --> continues posteriorly with a slight inferolateral inclination (forming the prominence of the facial canal in the medial wall of tympanic cavity) --> behind the base of the pyramidal eminence the nerve makes a broad turn to descend vertically and somewhat laterally (2nd genu) through the mastoid cavity
What is the average diameter of the IAC?
What is the upper limit of normal diameter of the IAC?
What is the narrowest intratemporal portion of the fallopian canal?
Entrance to the fallopian canal at the lateral aspect of the IAC (fundus)
What structure bisects the IAC in the vertical direction and in the horizontal direction?
Bill's bar; transverse/falciform crest
Below is a cross-sectional diagram of the IAC. Name the structures:
- A - facial nerve
- B - Superior branch of the vestibular nerve
- C - Cochlear nerve
- D - Inferior branch of the vestibular nerve
What does the superior vestibular nerve innervate?
- Superior and lateral SCCs
What does the inferior vestibular nerve innervate?
- Posterior SCC
- Macula of the saccule
Where is the 2nd genu of the facial nerve?
Just distal to the geniculate ganglion at the sinus tympani between the tympanic and mastoid segments
What is the relationship of the 2nd genu of the facial nerve to the lateral SCC and short process of the incus?
The 2nd genu is inferior to the lateral SCC and medial to the short process of the incus
In its tympanic segment, between which structures does the facial nerve travel?
- Superiorly - the lateral SCC
- Inferiorly - the oval window
Where does the facial nerve lie in relation to the cochleariform process?
What is the cog?
A ridge of bone that extends inferiorly from the tegmen epitympanum and partially separates the anterior epitympanic compartment from the mesoepitympanum
What is the relationship of the tympanic portion of VII to the cog?
VII lies anterior to the cog in the floor of the anterior epitympanum
What percentage of people have a dehiscence of the facial nerve in either the tympanic or mastoid segments?
50 - 55%
Where is the most common site of dehiscence?
Tympanic segment superior to the oval window
What is the last branch of the facial nerve before it passes through the stylomastoid foramen?
Where does the chorda tympani arise in relation to the stylomastoid foramen?
Usually 4-7mm superior
What artery accompanies the chorda tympani?
Posterior tympanic artery
What is the name of the opening through which the chorda tympani nerve enters the infratemporal fossa?
Petrotympanic fissure (canal of Huguier)
Where are the cell bodies of the motor fibers of the chorda tympani nerve?
Superior salivatory nucleus
What 3 motor branches does the facial nerve give off just after exiting the stylomastoid foramen?
- Nerve to posterior belly of digastric
- Nerve to the stylohyoid
- Nerve to the postauricular muscle
Where is the facial nerve trunk located in relation to the tympanomastoid suture line?
6-8mm anteroinferior (between the suture line and the styloid process)
What is the name of the point at which the facial nerve divides into the upper and lower divisions?
How far is the pes anserinus from the stylomastoid foramen?
How does facial nerve innervation to the upper face differ from that to the lower face?
- Upper motor neurons sending information to the upper face cross twice in the pons
- Upper motor neurons sending information to the lower face cross only once in the pons
- Therefore, lesions proximal to the nucleus only affect the lower face
True/False: There is a consistent topographic representation of fibers from a specific section of a nerve innervating certain parts of the face.