29 - Ear and Auditory Tube Flashcards
Name for the external ear
Auricle
Border between outer and middle ear
Tympanic membrane
Boundaries of the middle ear
Space between the tympanic membrane and petrous part of the temporal bone.
Location of the inner ear
Within the petrous part of the temporal bone
Alternative name for external auditory meatus
Ear canal
Composition of external auditory meatus
1) Lateral 1/3 is cartilagenous
2) Medial 2/3 is bony
3) Hairy skin with cerumen glands (make ear wax, prevent maceration of skin with water)
Innervation of external auditory meatus
1
2
3
1) Posterior is innervated by vagus
2) Anterior and superior is by auriculotemporal nerve (mandibular division of trigeminal nerve)
3) External surface of tympanic membrane by auriculotemporal nerve
Where can pain in tympanic membrane refer?
Inferior teeth (both innervated by auriculotemporal nerve, which branches from mandibular branch of trigeminal nerve.
Features of the surface of tympanic membrane
1) Flaccid area
2) Handle of malleus
3) Cone of light in antero-inferior quadrant.
4) Convex medially, concave laterally.
Two divisions of middle ear
1) Medial to the tympanic membrane is tympanic cavity proper
2) Superior to tympanic membrane is epitympanic recess
What does the epitympanic recess communicate with?
Mastoid air cells
Potential danger of epitympanic recess communicating with mastoid air cells
Infection of middle ear can ascend into air cells of mastoid process
Communication between tympanic cavity proper and nasopharynx
Auditory tube/Eustachian tube/pharyngotympanic tube.
Projects antreoinferiorly from tympanic cavity proper to nasopharynx
Role of Eustachian tube
Allows equalisation of pressure between nasopharynx and middle ear
Significance of antero-inferior path of Eustachian tube from middle ear to nasopharynx
1
2
1) Hard for bacteria to ascend from nasopharynx to middle ear.
2) Exudate from middle ear infection can drain into nasopharynx.
Why do infants get more middle ear infections?
Eustachian tube angle is much less inferior than adults.
Therefore easier for bacteria to ascend from nasopharynx to middle ear.
If chronic ear infections, can impair language development, as can’t hear properly.
Ossicles
Three bones that form a connection between tympanic membrane and sensory receptors in the inner ear.
Stapes
Incus
Malleus
Ossicle attached the medial surface of the tympanic membrane
Malleus
Ossicle that overlies oval window into inner ear
Stapes
Ossicle linking malleus and stapes
Incus
Important muscles in the middle ear
Tensor tympani (V), stapedius (VII)
What does tensor tympani connect with?
Attaches to malleus.
From anterior wall.
What does stapedius connect with?
Attaches to Stapes.
From posterior wall.
Role of stapedius and tensor tympani
Contract to prevent movement of malleus and stapes.
Reflex to protect ear from high-frequency, high-amplitude sounds.
Auditory sign associated with Bell’s palsy (damage to CNVII)
Very sensitive to loud sounds.
Can’t get reflex activation of stapedius in response to loud sounds.
Promontary
Swelling on the medial wall of the inner ear.
Sits near round window, oval window
Chorda tympani
Branch of the facial nerve. Nothing to do with innervation of the ear.
Special sensory for taste of anterior 2/3 of tongue.
Runs through middle ear, joins with lingual nerve (branch of mandibular division of CNV) to travel to tongue.
Artery running near middle ear
Internal carotid.
When there is fluid in the middle ear, can hear the pulse of the internal carotid.
Bony labyrinth
Space in the petrous temporal bone filled with perilymph.
Where the sensory parts of the inner ear sit
What separates perilymph of the bony labyrinth from the middle ear?
Membranes over oval window, round window.
Membranous labyrinth
Membranous sack containing endolymph.
Lies within bony labyrinth, suspended in perilymph.
Parts of bony labyrinth
1
2
3
1) Cochlea
2) Vestibule
3) Semicircular canals (three of these, an anterior, posterior and a horizontal)
What does the cochlea contain?
Parts of membranous labyrinth that contain sensory receptors for hearing
What do the semicircular canals contain?
Parts of membranous labyrinth that contain sensory receptors for moving equilibrium
What does the vestibule contain?
Parts of membranous labyrinth that contain sensory receptors for static equilibrium, vestibular nerves
Parts of membranous labyrinth involved in hearing
Cochlear duct, cochlear nerve
Parts of membranous labyrinth involved in dynamic equilibrium
Anterior, posterior, horizontal semicircular ducts.
Ampulla, vestibular nerves
Parts of membranous labyrinth involved in static equilibrium
Utricle, sacule.
Which nerves join in the internal auditory meatus to form the vestibulocochlear nerve?
Cochlear nerve and vestibular nerves.
Orientations of semicircular canals
Anterior points 45 degrees from midline of head.
Posterior points 45 degrees posteriorly from midline of head.
Horizontal points laterally.
Part of cochlea that detects high-frequency sounds
Base of cochlea
Part of cochlea that detects low-frequency sounds
Apex of cochlea
What is equilibrium?
Head position and movement
How is head movement detected?
Endolymph movement past sensory receptors in the ampulla.
How is static head position detected?
Gravity influences sensory receptors in the utricle and saccule.
