27 - Ear Flashcards
Where is the internal meatus located?
Petrous part of the temporal bone
Where is the external acoustic meatus located?
Lateral to the carotid canal
What makes up the external ear?
- auricle
- external acoustic meatus
- tympanic membrane
What makes up the middle ear?
- tympanic cavity
- malleus, incus and stapes
- tensor tympani, stapedius
- auditory tube
What makes up the inner ear?
- vestibule
- semicircular canals
- cochlea
How do the ossicles transmit sound?
Mechanically by vibrations
Describe the auricle.
- elastic cartilage
- funnels sound into the external acoustic meatus
- helix, tragus and lobule are notable cartilaginous structures
What is the sensory innervation of the auricle?
- great auricular
- auriculotemporal
Describe the external acoustic meatus.
- 2.5cm in length
- cartilaginous lateral 1/3, bony medial 2/3
- stratified squamous epithelium that contains ceruminous glands that secrete ear wax
Describe the tympanic membrane.
- held by a fibrocartilaginous ring
- at an angle facing downwards and anteriorly
- 1cm in diameter
- attached to the handle of the malleus, this forms the umbo
What is the cone of light?
Reflection of the otoscope indicating a healthy middle ear
What is the function of the middle ear muscles?
- dampen vibrations (protective)
- reduce movement of the ossicles
What is the attachment and action of the tensor tympani?
- attaches to malleus and pulls the tympanic membrane taught
- this reduces amplification of loud sounds
What is the innervation of tensor tympani?
CN V3
What is the innervation of stapedius?
CN VII
What is the attachment and action of stapedius?
- attaches to the stapes
- pulls stapes posteriorly to prevent excessive movement
What are the muscles of the middle ear?
- tensor tympani
- stapedius
Describe the auditory tube.
- also known as the pharyngotympanic tube
- connects middle ear with nasopharynx
- bony canal that becomes cartilaginous between the temporal and the greater wing of sphenoid
- pressure equalisation between middle ear and atmospheric pressure
- route for infection spread
What nerves enter the temporal bone at the the internal acoustic meatus?
- CN VII
- CN VIII
What is the clinical name for a middle ear infection?
Otitis media
How does infection affect the middle ear?
- often caused by obstruction
- chronic infection can affect the ossicles causing conductive deafness
- infection can spread to the mastoid air cells laterally
What is conductive hearing loss?
Hearing loss caused by damage to the mechanical structures rather than nerve damage
What is the function of the cochlea?
Hearing
What is the function of the vestibule?
Balancing
What is the otic capsule?
The bone surrounding the labyrinth
What is the labyrinth?
- the fluid filled spaces within the capsule
- contains the cochlea, vestibule and semicircular canals
What fluid is within the bony labyrinth?
- perilymph
- the membranous labyrinth is suspended in the perilymph
What fluid is within the membranous labyrinth?
Endolymph
What is the innervation of the inner ear?
Vestibulocochlear nerve
What does the cochlear part of CN VIII innervate?
Cochlea
What does the vestibular part of CN VIII innervate?
- saccule
- utricle
- semicircular canals
What does damage to the cochlear part of CN VIII cause?
Neural hearing loss
What does damage to the vestibular part of CN VIII cause?
- ataxia
- vertigo
- nausea
