The External and Middle Ear Flashcards
Innervation of the auricle? -4
- -greater auricular,
- -lesser occipital
- Facial CN7 branches
- Vagus CN10 branches
Why can cleaning your ears sometimes cause you to cough?
Can stimulate the auricular branch of the vagus nerve Vagus nerve is responsible for the cough reflex
Vasculature of the auricle? -2
Posterior auricular,
superficial temporal
What is the external acoustic meatus?
Sigmoid shaped tube extending from the deep part of the concha to the tympanic membrane
What gives the external acoustic meatus structure?
Cartilage from the auricle + Bony support from the temporal bone
Innervation of the external acoustic meatus? -2
- Mandibular CN5B3
- Vagus CN10
Describe the direction that the external acoustic meatus travels
Initially superioanterior Then superioposterior Then inferioanterior
What are the 3 layers of the tympanic membrane?
- Outside = skin
- Core = Connective tissue
- Inside = Mucous membrane
What is the tympanic membrane connected to?
Surrounding temporal bone by a fibrocartilaginous ring
How is the malleus attached to the tympanic membrane?
The handle of malleus attaches at the umbo and Continues superiorly
What are the parts of the membrane moving away from the tympanic membrane called? -2
Anterior and posterior mallear folds
What is an auricular hematoma?
blood collection between cartilage and overlying perichondrium usually as a result of trauma
What can an auricular haematoma lead to and how?
Accumulation of blood disrupts the vascular blood supply to the cartilage of the pinna so if not drained quickly, can –> cauliflower ear
Main causes of tympanic membrane perforation - 2
- Trauma
- Otitis media (purulent fluid build up –> rupture)
Function of the auricle?
Captures and transmits sound to the external acoustic meatus
Which bone does the middle ear lie within?
temporal bone
Where does the middle ear extend from and to?
From the tympanic membrane to the lateral wall of the internal ear
Purpose of the middle ear?
Transmit vibrations from the tympanic membrane to the inner ear via three bones
Sections of the middle ear? -2
- Tympanic cavity - medial to the tympanic membrane and contains majority of bones of the middle ear
- EpiTympanic recess - superiorly, near mastoid air cells
Borders of the middle ear?
Roof / Lateral / Floor / Medial / Posterior / Anterior
Visualised as a rectangular box
Roof: Petrous temporal bone
Lateral: TM and epitympanic recess
Floor: “Jugular Floor” Thin layer of bone separates it from internal jugular
Medial: lateral wall of inner ear
Posterior: “Mastoid Wall” A bony partition between the tympanic cavity and mastoid air cells. Hole in the partition superiorly allowing communication called the aditus to the mastoid antrum
Anterior: thin bony plate with two openings for the auditory tube and tensor tympani muscle. Separates mid ear from internal carotid
What does the Middle Ear roof separate the middle ear from?
Middle cranial fossa
What makes a bulge in the medial wall of the inner ear?
Facial CN7
Names of the auditory ossicles? -3
MIS ossicle bones
Malleus
Incus
Stapes
Where does the head of the malleus lie?
Epitympanic recess where it articulates with the incus
What are the muscles called in the middle ear? -2
Tensor tympani and stapedius
Function of the muscles of the middle ear?
Contract in response to loud noise, inhibiting vibrations of the bones Reduces transmission of sound to the inner ear Called the acoustic reflex
Describe attachment of Middle ear muscles -2
- Tensor tympani: from auditory tube to handle of malleus, pulling malleus medially
- Stapedius: attaches to stapes
Innervation of the middle ear muscles? -2
Tensor tympani = [Mandibular CN5B3]
Stapedius - Facial CN7
Where are the mastoid air cells located? What are they?
Posterior to the epitympanic recess within the [mastoid antrum cavity] of temporal bone; Collection of air-filled spaces
Function of the mastoid air cells?
Act as a buffer system - release air into the tympanic cavity when pressure is too low
How do the mastoid air cells communicate with the middle ear?
Aditus to middle antrum
What two things does the EPAT [Eustachian Pharyngotympanic Auditory Tube] connect?
Mid ear to nasopharynx
Function of the EPAT [Eustachian Pharyngotympanic Auditory Tube]?
Equalizes pressure of middle ear to that of the external auditory meatus
What is cholesteatoma?
Growth of stratified squamous epithelium in the middle ear
Congenital vs Acquired
What problems can cholesteatoma cause?
Damage bones of middle ear due to increase pressure & Releases osteolytic enzymes
Patients present with hearing loss and sometimes facial nerve palsy
How to treat cholesteatoma?
Surgical removal
What is mastoiditis?
Otitis media can spread to the mastoid air cells, as its a good site for pathogenic replication
Complications of mastoiditis?
Mastoid process gets infected and can spread to middle cranial fossa causing meningitis
How is mastoiditis treated?
Pus is drained from air cells, careful of nearby facial nerve
What is glue ear?
Otitis media with effusion
How does otitis media with effusion occur?
AKA Glue Ear
persistent dysfunction of EPAT (blockage, inflammation, genetic mutation) –> inability to equalize middle ear pressure –> negative pressure develops inside middle ear which draws out transudate from mucosa of the middle ear –> Glue Ear infection
EPAT [Eustachian Pharyngotympanic Auditory Tube]
Why are children more prone to infection? -2
EPAT is shorter and more horizontal
EPAT [Eustachian Pharyngotympanic Auditory Tube]
Which opening does the Stapes Base articulate
OV (Oval Vestibular) window
Which opening does the Scala Tympani articulate
RC (Round Cochlear) window
What role does the external ear play in hearing?
Collects sound
What role does the middle ear play in hearing?
Amplifies sound
What role does the inner ear play in hearing?
Transduces sounds
What is the speed of sound in air?
330m/s
Does sound travel faster or slower in water than air?
Faster
What frequencies should humans hear ?
20 - 20,000 Hz
What range of frequencies are tested on an audiogram?
250Hz to 6000Hz
What does the frequency of a sound wave do?
Dictates how high or low
What does the amplitude of a sound wave do?
Dictates loudness
In the middle ear, how is sound amplified?
Stapes hits against the oval window with greater force when vibrations are higher
What ligament suspends the stapes bone?
Annular ligament
What muscles are related to the stapes bone?
Stapedius Tensor tympani
What muscles open the Eustachian tube?
Tensor veli palatini Levator palatine
What manoeuvre can be done to equalise the ears?
Valsalva manoeuvre
What can cause glue ear to be more common?
Cleft palate which causes the muscles which open the eustachian tube to be dysfunctional
Through which window is sound waves transmitted?
Oval
What is the round window for?
Allows pressure to leave
Where is the sound actually perceived?
The fine hairs on the cochlea
What nerve transmits the sound vibrations to the brain?
Cochlear nerve
What bone is the inner ear located in?
Petrous part of the temporal bone
Where is perilymph?
Within the bony labyrinth
Where is the endolymph?
Within the membranous labyrinth
What makes up the membranous labyrinth?
3 semicircular ducts- anterior, posterior and lateral
What connects each semicircular duct to its base- the utricle?
The ampulla
What sensory organ is contained within the ampulla?
Cristae ampullaris
What happens when endolymph moves against the cristae ampullaris?
Hair cells become depolarised which sets up an action potential
What separates the endolymph and perilymph?
Basilar membrane
How does gentamicin cause tinnitus?
It causes damage to the outer hair cells
What is another name for stereo cilia?
Inner hair cells
What is meant by tonotopic organisation of the cochlea?
Different areas of the basilar membrane are responsible for different frequencies of sound
Where it the apex of the cochlea?
Furthest from the round window i.e. centre of spiral
What are the two otolith organs called?
Utricle Saccule
What structure is responsible for vertigo and what are they made of?
Otoconia Calcium carbonate crystals
What is special about the orientation of the semicircular canals?
They are orientated at 90 degrees to each other and are paired.
What causes deflection?
Movement of endolymph by bodily movement causes the stereocilia to deflect
What is spontaneous nystagmus?
Movement of the eye without a stimulus
