L17 & L18 - Middle ear and facial nerve Flashcards
Tympanic cavity: what is it, where is it located, what are its anatomical relations, and what does it do?
Air-filled chamber in the petrous part of the temporal bone
Just at the end of the sigmoid groove
- Tympanic cavity proper medial to the tympanic membrane
- Epitympanic recess superomedial to the tympanic membrane
Transmits sound from the outer ear
Tympanic cavity: what is contained in it and what is it in communication with?
- The auditory ossicles (malleus, incus and stapes)
- Tensor tympani and stapedius muscles
- Chorda tympani (branch of the facial nerve, CN VII)
- Tympanic nerve plexus
The nasopharynx via the eustachian tube and the mastoid air cells via the aditus and mastoid antrum
Mastoid ear cells
Dead end - travels down the inferior part of the mastoid process and no further
Near the pinna
What are the walls of the tympanic cavity?
Roof - tegmental wall
Floor - jugular wall
Lateral wall - membraneous wall
Medial wall - labyrinthine wall
Anterior wall - carotid wall
Posterior wall - mastoid wall
Tegmen tympani
Has a name
Tegmental wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Formed from tegmen tympani, a thin plate of bone
Separates tympanic cavity from middle cranial fossa (and brain)
Jugular wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Formed from bone
Separates tympanic cavity from the superior bulb of the internal jugular vein
Membraneous wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Part of the lateral wall
Formed from the tympanic membrane and lateral bony wall of the epitympanic recess
Separates tympanic cavity from the external ear
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Labyrinthine wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Part of the medial wall
Formed from the lateral wall of the vestibule (including the oval window) and initial turn (including the round window) of the cochlea
Separates tympanic cavity from the inner ear
Mastoid wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Aditus links tympanic cavity to the antrum which in turn communicates with the mastoid air cells
Facial nerve canal is between the antrum and the posterior wall of the tympanic cavity
- Contains bony air holes which allows it to stay strong and light
- Sternocleidomastoid (and other muscles) attached to it
- Lines with mucous membrane that is continuous with the lining of the tympanic cavity
- Tegmen tympani separates the antrum from the middle cranial fossa
Carotid wall: what part of the tympanic cavity wall is it, what is it formed from and what does it do?
Part of the anterior wall
Contains openings of the pharyngotympanic tube
and the canal for the tensor tympani
Separates tympanic cavity from the carotid canal (and internal carotid artery)
Pathology of the facial nerve
Forceps around baby’s head - the mastoid process not protecting facial nerve yet
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Separates tympanic cavity from the carotid canal (and internal carotid artery)
Ossicles within the middle ear: what are they, what do they do, and where are they derived from?
Incus, Malleus, stapes
- Transmit sound from the tympanic membrane to the cochlear
- Increase the force of sound waves (x10-20)
- Maintain the frequency of the sound waves
Splanchnocranium:
Incus (maxillary cartilage)
Malleus (Meckel’s cartilage)
Stapes (Reichert’s cartilage)
Incus, malleus, stapes: what items are they often related to due to their shapes?
Incus - anvil
Malleus - hammer
stapes - stirrup
Why do we increase sound wave force when it enters the ear?
Density
Moving through the air is several times easier than moving through the more dense liquid within the ear so an increase in sound wave force is required
Incus: what is it, what does it do, and what do its specific parts do?
Body of incus (anvil) is in epitympanic recess and articulates with the malleus
Transmits vibrations from the malleus to the stapes
- Long limb articulates with head of the stapes
- Short limb is connected by a ligament to the posterior of the tympanic cavity
Malleus: what is it, what does it do, and where do its specific parts articulate to?
Handle of malleus (hammer) is embedded in the tympanic membrane
transmit sound from the tympanic membrane (ear drum) to the inner ear
- Neck lies against the flaccid part of the tympanic membrane
- Head in epitympanic recess and is in contact with incus
Stapes: what is it, what does it do, and where do its specific parts articulate to?
Stapes (stirrup) is the smallest ossicle (and the smallest bone in the body) which fits into the oval window of the medial wall
Transmits sound waves to the cochlear
- Has a head, neck, two limbs and a base
Reflex to loud noise: which muscles act and what do they do?
Protect inner ear hair cells, instinctively contract tensor tympani and stapedius muscles to reduce damage
- Reduce vibrations when contracted by moving the stapes away from the oval window and reducing vibration transmission
- Protect against loud noises
If this is dulled ears become damaged
Tensor tympani: what is it, where is its origin, where does it insert, and what is it innervated by?
Muscle that can decrease sound transmission through the middle ear
Has origin on the cartilaginous part of the pharyngotympanic tube, greater wing of the sphenoid and temporal bone
Inserts onto handle of malleus and tenses tympanic membrane
Innervated by the mandibular nerve (V3)
Stapedius: what is it, where is its origin, where does it insert, what is it innervated by, what can occur if it is damaged, and are there any key facts about it?
Muscle that directly acts on the stapes
Origin inside pyramidal eminence of posterior wall
Inserts onto neck of stapes and pulls it posteriorly and tilts its base in the oval window
Innervated by a branch of the facial nerve (VII)
Hyperacusis – distorted and echoing sounds due to stapedius paralysis
Smallest muscle in the body
Pharyngotympanic tube: what is its other name, what does it do, what is its structure, how does it exit, and what other key details does it have?
Eustachian tube
Communicates with the nasopharynx and equalises pressure between middle and external ears
Postero-lateral third is bony, the remainder is cartilaginous
Exits through foramen lacerum
- Lined with mucous membrane
- Walls normally in contact
- Can be opened by contracting tensor veli palatini and levator veli palatini I.e. by yawning or swallowing
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