Region 14 - Ear Flashcards by Daniel Part

What structures make up the external ear?

Auricle
External auditory meatus
External surface of tympanic membrane

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What structures make up the middle ear?

Internal surface of tympanic membrane
Tympanic cavity
Ossicles
Pharyngotympanic tube

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What structures make up the inner ear?

Auditory apparatus
Vestibular apparatus
Internal acoustic meatus
CN VIII
Oval window
Round window

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What is the auricle made up of?

Irregularly-shaped plate of elastic cartilage

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Where does lymph from the auricle drain to?

Parotid and cervical nodes

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What is the arterial supply to the auricle from?

Anterior auricular branches of superficial temporal artery

Posterior auricular artery perforating branches

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What is the concha of the auricle? What is it made up of?

The deepest depression
Formed from:
- Cymba (superiorly)
- Cavity (inferiorly)

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What is the sensory innervation to the auricle?

Anteriorly = Auriculotemporal nerve (CN V3)
Posteriorly = Lesser occipital nerve (C2) and Greater auricular nerve (C2-C3)
Entire auricle = Facial nerve contributions
Concha = Vagus nerve contributions

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How long is the EAM?

~2.5cm

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What type of cartilage makes up the lateral 1/3 of the EAM?

Elastic

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What features are present in the lateral 1/3 of the EAM?

Hair follicles
Sweat glands:
- Ceruminous glands
Sebaceous glands

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How does earwax form?

Mixing of secretions from sweat glands and sebaceous glands in lateral 1/3 of EAM

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What is the structure of the medial 2/3 of the EAM?

Bone

Lined with stratified squamous epithelium

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What is the arterial supply to the EAM?

Auricular branches of ECA

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What is the sensory supply to the EAM?

External surface = Auriculotemporal nerve (CN V3)
Anterosuperiorly = Auriculotemporal nerve
Posteroinferiorly = Auricular branch of CN X
Posteriorly = Posterior auricular branch of CN VII

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What is the diameter of the tympanic membrane?

~8mm

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What is the outer surface of the tympanic membrane lined with?

Stratified squamous epithelium

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What is the inner surface of the tympanic membrane line with?

Mucous membrane

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What neurovascular structure crosses the inner surface of the tympanic membrane?

Chorda tympani of CN VII

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What ossicle attaches to the inner surface of the tympanic membrane?

Malleus

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What is the innervation to the lateral (external) surface of the tympanic membrane?

Auriculotemporal nerve (anteriorly and superiorly)
Auricular branch of CN X (posteroinferiorly)

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What is the innervation to the medial surface of the tympanic membrane?

Tympanic branches of CN IX

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What forms the roof of the tympanic cavity (middle ear)?

Tegmen tympani:

Part of petrous temporal bone
Separates middle ear from dura of middle cranial fossa

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What forms the floor/jugular wall of the tympanic cavity (middle ear)?

Layer of bone between:

Tympanic cavity AND
Superior bulb of IJV

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What forms the membranous/lateral wall of the tympanic cavity (middle ear)?

Tympanic membrane Superiorly: - Lateral bony wall of epitympanic recess - Head of malleus extends into recess

What forms the labyrinthine/medial wall of the tympanic cavity (middle ear)?

Promontory of labyrinthine wall: - Basal turn of cochlea - Oval and round windows

What overlies the promontory of the labyrinthine wall of the tympanic cavity?

Tympanic plexus: - Lesser petrosal nerve - Tympanic nerve (Both CN IX)

What forms the mastoid/posterior wall of the tympanic cavity (middle ear)?

Aditus: - Opening in superior aspect of cavity - Opens into mastoid antrum

What forms the carotid/anterior wall of the tympanic cavity (middle ear)?

A thin bone between the tympanic cavity and the carotid canal

What features are in the superior part of the anterior wall of the tympanic cavity?

Opening for pharyngotympanic tube | Canal for tensor tympani

What is the origin and insertion of tensor tympani?

``` Origin = Wall of pharyngotympanic tube Insertion = Handle of malleus ```

What is the function of tensor tympani?

Tenses tympanic membrane by pulling handle of malleus medially

What is the innervation to tensor tympani?

CN V3

What is the origin and insertion of stapedius?

``` Origin = Pyramidic eminence on posterior wall of tympanic cavity Insertion = Neck of stapes ```

What is the function of stapedius?

Pulls 'footplate' of stapes laterally

What is the innervation to stapedius?

Nerve to stapedius from CN VII

What is the combined action of tensor tympani and stapedius?

Reduces vibration passing to delicate inner ear at the oval window

What nerve provides sensory supply to the tympanic cavity?

CN IX

What is the arterial supply to the tympanic cavity?

``` Tympanic branches of: - Posterior auricular artery - Ascending pharyngeal artery - Maxillary artery Caroticotympanic artery from ICA ```

How does the chorda tympani leave the tympanic cavity?

Via the petrotympanic fissure

What is the structure of the lateral part of the pharyngotympanic tube?

1.2cm long Bony canal Lined with mucous membrane

What is the structure of the medial part of the pharyngotympanic tube?

2.5cm | Cartilaginous and membranous tube

What causes the pharyngotympanic tube to open?

Swallowing or yawning: - Tensor veli palatini contracts - Lumen opens

What is the purpose of opening the pharyngotympanic tube?

Equalises pressure on both side of tympanic membrane

What is the sensory supply to the pharyngotympanic tube?

Nerves from tympanic plexus (CN IX)

What is the main arterial supply to the middle ear?

Anterior tympanic (glaserion) artery from 1st part (mandibular) of maxillary artery

What other arteries supply the middle ear?

Ascending pharyngeal (inf. tympanic artery) Middle meningeal (superior tympanic artery) Posterior auricular: - Stylomastoid artery - Posterior tympanic artery Artery of pterygoid canal Caroticotympanic branch of ICA

What surrounds the bone labyrinth of the inner ear?

Otic capsule: - Very dense bone within petrous temporal bone - NOT a part of bony labyrinth

What are the canals of the bony labyrinth filled with?

Perilymph (similar to ECF)

What are the structures of the bony labyrinth?

Cochlea Vestibule Semicircular canals

What is the membranous labyrinth?

A continuous system of ducts and sacs within bony labyrinth

What is the membranous labyrinth suspended in?

Perilymph

What is the membranous labyrinth filled with?

Endolymph (similar to potassium ion-rich ICF)

What are the functions of perilymph and endolymph?

Conduct sound vibrations Respond to mechanical forces: - Movement - Acceleration

What are the three main canals within the cochlea?

Scala vestibuli Scala tympani Cochlear duct

What canal within the cochlea communicates with the stapes and where?

Scala vestibuli | At the oval window

What canal within the cochlear communicates with the tympanic cavity and where?

Scala tympani | At the round window

What are the scala vestibuli and scala tympani filled with?

Perilymph

What separates the scala vestibuli and scala tympani?

Reissner's membrane

What is the cochlear duct filled with?

Endolymph

What organ of hearing is found within the cochlear duct?

Organ of Corti

How many turns does the cochlear have?

2.5

What does the spiral canal of the cochlea turn around?

A bony core = Modiolus

Where do the scala vestibuli and scala tympani communicate?

Helicotrema

Where do the semicircular canals lie in relation to the vestibule?

Posterolaterally

What is the structure of a semicircular canal?

2/3 of a circle | Diameter of ~1.5mm

What are the semicircular canals?

Anterior and posterior (lie at right angles) | Lateral (lies horizontally)

What are the semicircular ducts continuous with?

Utricle

What is the swelling at the end of each semicircular canal? What does this contain?

Ampulla Contains: - Crista ampullaris which contains equilibrium sensors

What do the ampullae of the semicircular canals respond to?

Angular (rotational) movements of the head

How long is the vestibule of the bony labyrinth?

~5mm

What membranous sacs are within the vestibule of the bony labyrinth?

Utricle | Saccule

What equilibrium sensors are contained within the utricle and saccule? What movements do they respond to?

Maculae Respond to: - Gravity - Changes in head position

What is the main arterial supply to the inner ear?

Internal auditory (labyrinthine) artery

What is the origin of the main arterial supply to the inner ear?

``` Anterior inferior cerebellar artery (85%) Basilar artery (15%) ```

What are the branches of the main arterial supply to the inner ear?

Common cochlear artery | Vestibular artery