The External and Middle Ear Flashcards
Innervation of the auricle?
Cutaneous innervation
-greater auricular, lesser occipital and branches of facial and vagus nerves
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?
Posterior auricular, superficial temporal, occipital arteries and veins
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?
Sensory innervation
-branches of the mandibular and vagus nerve
Describe the direction that the external acoustic meatus travels
Initially superioanterior
Then superioposterior
Then inferioanterior
What are the two layers of the tympanic membrane?
Skin on the outside
Mucous membrane on the inside
Core of connective tissue
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 umbro
Continues superiorly and it has a lateral process of malleus at its highest point
What are the parts of the membrane moving away from the tympanic membrane called?
Anterior and posterior malleolar folds
What is an auricular haematoma?
When blood collects between cartilage and overlying perichondrium usually as a exult 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 get a cauliflower ear
What can perforate the tympanic membrane?
Trauma or infection
Otitis media causes pus and fluid to build up causing an increase in pressure so that is eventually ruptures
Membrane normally heals itself, but may require surgery
Function of the auricle?
Captures and transmits sound to the external acoustic meatus
Which bone does the middle ear lie within?
The 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?
Tympanic cavity - medial to the tympanic membrane which contains the majority of bones of the middle ear
Epitympanic recess - superiorly, near mastoid air cells
Borders of the middle ear?
Visualised as a rectangular box
Roof: thin bone from petrous part of temporal bone.
Floor: ‘jugular wall’. Thin layer of bone separates it from internal jugular
Lateral: tympanic membrane and epitympanic recess
Medial: lateral wall of inner ear
Anterior: thin bony plate with two openings for the auditory tube and tensor tympani muscle. Separates mid ear from internal carotid
Posterior: aka 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
What does the roof separate the middle ear from?
Middle cranial fossa
What makes a bulge in the medial wall of the inner ear?
Facial nerve
Names of the auditory ossicles?
Malleus
Incus
Stapes
What do they connect?
Tympanic membrane to the oval window of the internal ear
Where does the head of the malleus lie?
Epitympanic recess where it articulates with the incus
What does the incus consist of and what does it articulate with?
Body and two limbs
Body articulates with malleus
Short limb attaches to posterior wall
Long limb to the stapes
Shape of the stapes? Articulations?
Stirrup shaped - head, two limbs and a base
Head with incus
Base to oval window
What are the muscles called in the middle ear?
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
Attachments of the muscles?
Tensor tympani: from auditory tube to handle of malleus, pulls it medially
Stapedius: attaches to stapes
Innervation of the muscles?
Tensor tympani - branch of mandibular nerve
Stapedius - facial nerve
Where are the mastoid air cells located? What are they?
Posterior to the epitympanic recess
Collection of air-filled spaces in the mastoid process of the temporal bone
Contained within a cavity called the mastoid antrum
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 Eustachian tube connect?
Middle ear to the nasopharynx
Function of the Eustachian tube?
Equalises pressure of middle ear to that of the external auditory meatus
What is cholesteatoma?
Growth of stratified squamous epithelium in the middle ear
Can be congenital or 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?
Surgery to remove it
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 arise?
Arises from persistent dysfunction of auditory tube
If tube is unable to equalise middle ear pressure (blockage, inflammation, genetic mutation), a negative pressure develops inside the middle ear which draws out transudate from the mucosa of the middle ear
Creates an environment suitable for pathogens to replicate and cause infection
How does the ear drum appear in glue ear?
Inverted, fluid visible
Why are children more prone to infection?
Eustachian tube is shorter and more horizontal
