HNS61 Ear Flashcards
External features of Ear / Auricle
ALL are yellow cartilages (like Epiglottis) except lobule
- Helix (耳殼)
- Antihelix
- Lobule (fat)
- Tragus
- Antitragus
- Crus of helix
Ear can move a little by extrinsic + intrinsic muscle (CN7)
***External auditory canal / External acoustic meatus
- 3cm long
- narrowest part (Isthmus) close to membrane
- not straight: pull upwards and backwards to straighten
- lined by sensitive skin
- vibrating air transmitted to Tympanic membrane
- External 1/3: Cartilage
- Internal 2/3: Bone
- ceruminous glands (esp. in cartilaginous part) —> ear wax —> accumulation of ear wax —> block canal —> impacted wax —> conductive deafness
Nerve supply:
- ***CNV3 (main)
- CN7 + CN10 —> referred pain from lower teeth
Blood supply:
- ***Posterior auricular artery (ECA)
- ***Superficial temporal artery (ECA)
Lymphatic:
- ***Superficial Cervical LN along EJV
***Ear pathway
External ear:
- Ear (Auriculotemporal nerve CNV3)
- External auditory canal / External acoustic meatus (CNV3 + CN7 + CN10)
Middle ear (Tympanic plexus: CN9):
- Tympanic cavity (air-filled, lined by mucosa)
- Mastoid antrum + Mastoid air cells
- Promontory
- Auditory tube - Auditory tube (Pharyngotympanic tube) —(Anteromedial)—> Nasophaynx
Inner ear:
- Cochlea / Organ of corti (CN8) —> Hearing
- Semicircular canal (CN8) —> Balance / Spatial orientation
- Anterior / Lateral / Posterior
Tympanic membrane
Orientation: Upper end tilt towards outside (lateral side)
- Lateral process of malleus
- Handle of Malleus (run posteroinferiorly)
- Umbo (allow attachment of Handle of Malleus)
- Pars flaccida (area above Lateral process of malleus which is lax)
- Pars tensa (area posterior to Lateral process of malleus which is tense)
- Cone of light
- Long limb of Incus
***Middle ear supply
Nerve:
- ***Tympanic plexus (CN9) (Sensory) (CN7 (motor?))
Arterial supply:
- ***Branches of ECA
Venous:
- ***Pterygoid venous plexus
Lymphatics:
- ***Superior deep cervical LN / parotid LN
***Auditory tube
Anterior 2/3: Cartilage
- upside-down “J”
- completed by fibrous tissue
- Respiratory epithelium with lots of mucous glands
Posterior 1/3: Bone (Petrous temporal bone)
- thin epithelium, without glands
- evaporation from blood vessels keep it wet
Isthmus: narrowest part, junction between cartilage and bone part
Auditory tube
- leads to Nasopharynx (opening of auditory tube: behind base of ***Medial pterygoid plate)
—> Tubal eminence (in nasopharynx)
—> Tensor veli palatini (lateral) (CNV3) + Levator veli palatini (medial) (Pharyngeal plexus)
—> Tense + Elevate soft palate
—> Open auditory tube to introduce air into Middle ear
(∵ air in middle ear constantly absorbed into blood vessels —> pharyngeal air replaces)
Arterial supply:
- ***Ascending pharyngeal arteries (ECA)
- ***Middle meningeal arteries (Maxillary artery, through Foramen spinosum: lateral to Auditory tube)
Venous:
- ***Pterygoid venous plexus
Otitis media
Causes:
- Infections from pharynx reaching middle ear via Auditory tube
- Obstruction of Auditory tube
Group:
Young children <10 (Shorter, Horizontal, Wider auditory tube)
Investigation:
- Bulging of Tympanic membrane into external auditory canal
- Colour of Tympanic membrane (indicate disease)
- **Complications:
1. Hearing damage
2. Mastoiditis (spread to mastoid antrum)
3. Damage structures deep to walls (e.g. CN7)
4. Spread to Cranial cavity via middle / posterior cranial fossa by resorbing bone —> spread to brain
Treatment:
- Drain mastoid antrum at ***Suprameatal triangle (above and posterior to external auditory canal)
- Antibiotics
Middle ear effusion
Build up of fluid in middle ear
—> incise a hole behind cone of light (i.e. posterior and inferior of ear drum)
—> Myringotomy (drain fluid from middle ear)
Tympanic cavity of Middle ear
3 ossicles (All joined by synovial joints, ligaments stabilise ossicles):
- Malleus (lateral)
- attached to Umbo of Tympanic membrane by Handle - Incus (middle)
- Stapes (medial)
- base connect to Cochlea through Fenestra vestibuli (small membrane)
—> form a lever system —> Displacement reduced + Pressure increased
Orientation of Labyrinth in skull / Inner ear
- Internal acoustic meatus (Middle)
- entry of CN7, CN8 - Cochlea (Anterior) (CN8) —> Hearing
- Semicircular canal (Posterior) (CN8) —> Balance / Spatial orientation
- 3 canals: Anterior / Lateral / Posterior
- posterolateral to Cochlea
- coordinates with Cerebellum
***Anterior wall of Middle ear
- Auditory tube (anteromedial)
-
**Tendon of Tensor tympani (CNV3)
- Tendon attached to Handle of Malleus
- runs laterally, around Processus cochleariformis to connect to Malleus
- **Dampen loud sound - ***Greater petrosal nerve (parasympathetic + special visceral sensory fibres)
- pass through anterior wall —> Foramen lacerum —> join Deep petrosal nerve —> nerve to Pterygoid canal -
**Lesser petrosal nerve
- from **Tympanic plexus —> anterior wall —> Foramen ovale —> Otic ganglion —> Auriculotemporal nerve —> Parotid gland - ***Chorda tympani
- pass through Petrotympanic fissure —> joins Lingual nerve (CNV3) —> Taste + Salivary secretion (Submandibular ganglion —> Submandibular + Sublingual glands) - Processus cochleariformis
- Tendon of Tensor tympani runs around
***Posterior wall of Middle ear
- Opening to Mastoid antrum (posterior)
- infection can spread to Mastoid antrum -
**Mastoid antrum + Mastoid air cells
- air-filled space
- lies in Petrous temporal below Posterior cranial fossa
- regulate **Temperature + Pressure of middle ear
- Mastoid air cells developed from Mastoid process - Pyramid
- bony structure with fibres of Stapedius within
- Stapedius tendon from tip of Pyramid to neck of Stapes -
**Stapedius (CN7)
- origin: Pyramid
- Tendon attached to Handle of Stapes
- **Dampen loud sound -
**Chorda tympani (taste from anterior 2/3 tongue)
- pass through posterior wall from outside —> behind Malleus —> exit through anterior wall through **Petrotympanic fissure —> joins Lingual nerve (CNV3)
***Medial wall of Middle ear
- Fenestra vestibuli (Oval window)
- attachment of Stapes - Fenestra cochlea
- below Fenestra vestibuli
- for pressure release (nothing attaches) - ***Promontory (Bulge of Cochlea’s basal turn)
- location of Tympanic plexus (submucosal plexus) (CN9 Tympanic branch + some sympathetics) - ***Bulge of Lateral SCC (superior, posterior)
Medial to medial wall:
- ***CN7
- pass into Geniculate ganglion at the end of Internal acoustic meatus —> run posteriorly —> bulge in bone in medial wall - Geniculate ganglion
- CN7 —> Internal acoustic meatus —> Geniculate ganglion
—> pass around Posterior wall —> Chorda tympani —> Anterior wall
OR
—> pass around Posterior wall —> Continue inferiorly —> exit through Stylomastoid foramen
OR
—> Greater petrosal nerve —> Anterior wall
Lateral wall of Middle ear
- Occupied entirely by Tympanic membrane
- lined externally by skin, medially by mucosa
- Postero-inferior quadrant may be incised safely in operation of middle ear (middle ear effusion / Myringotomy)
Roof of Middle ear + Inner ear
-
**Tegmen tympani (Roof of middle ear: **thinnest part petrous bone of temporal bone)
- Middle cranial fossa above —> Meninges + Temporal lobe (infection can spread to here)
- ***Epitympanic recess (space between ossicles and Tegmen tympani) - Arcuate eminence (Roof of inner ear)
- impression of Anterior SCC —> upward projection of petrous temporal bone into cranial cavity
