What is the medical term for the external ear? What is its function?
Function – Transmits and captures sound to the external acoustic meatus
What is the cutaneous innervation of the external ear?
greater auricular, lesser occipital, branches of facial and vagus
Why does cleaning of the ears result in a cough reflex?
due to stimulation of the auricular branch of the vagus nerve
What is the vasculature of the external ear?
Posterior auricular, superficial temporal, occipital arteries and veins
What is an auricular haematoma? What does it result from? What can it result in?
Blood collects between cartilage and pericondrium overlying it
Usually results from trauma
Accumulation of blood disrupts vascular supply to cartilage of the pinna. If it is not drained, can result in cauliflower ear.
Where does the external acoustic meatus extend from?
extends from concha to tympanic membrane
What gives the external acoustic meatus its structure?
temporal bone and cartilage from auricle
What is the external acoustic meatus innervated by?
Innervated by mandibular and vagus nerves
Describe the structure of the tympanic membrane.What is the bone that attaches to the tympnaic membrane and where does it do so?
Double layered structure with skin on outside, mucous membrane on inside.
Core is CT. Connected to temporal bone by a fibrocartilaginous ring.
Handle of malleus attaches to tympanic membrane at a point called the umbro of the tympanic membrane
What can perforate the tympanic membrane?
Can be caused by trauma and infection.
Infection of middle ear causes pus and fluid to build up, resulting in increase in pressure and eventual rupturing of eardrum
In which bone does the middle ear lie?
What are the 3 bones of the middle ear from tympanic to inner ear order?
malleus, incus, stapes
What are the roof and floor borders of the middle ear
Roof – Petrous part of temporal bone
Floor – Jugular wall
What are the lateral and medial borders of the middle ear? What nerve travels in the medial wall?
Lateral wall – TM
Medial wall – Internal ear wall. Has bulge due to facial nerve which travels nearby
What are the anterior and posterior borders of the middle ear? What structures go through the anterior wall? What is the hole in the posteriro wall called?
Anterior wall – thin bony plate with openings for auditory tube and tensor tympani muscle
Posterior wall – AKA mastoid wall. Bony partition between Epitympanic recess and mastoid air cells. Hole in this partition called the aditus to the mastoid antrum.
What is a cholesteastoma? How does it cause damage and how does it present?
- This is a growth of stratified squamous epithelium in the middle ear
- Can be congenital or acquired
- Grows and causes damage to bones of middle ear by increased pressure or release of osteolytic enzymes
- Patients present with hearing loss and may have facial nerve palsy due to close proximity of facial canal. Treat surgically.
What are the 2 muscles of the inner ear?
Tensor tympani and stapedius
What is the function of the middle ear muscles?
Contract in response to loud noise and inhibit vibrations of malleus, incus and stapes, reducing transmission of sound to the inner ear. Known as the acoustic reflex.
What innervates the 2 middle ear muscles? Which bones do they attach to?
Tensor tympani attaches to malleus, innervated by mandibular
Stapedius attaches to stapes and innervated by facial
How do the mastoid air cells communicate with the middle ear?
aditus to mastoid antrum
What is the function of the mastoid air cells?
Mastoid air cells act as a buffer system of air, releasing air into tympanic cavity when pressure is too low.
What is mastoiditis? Why is the area prone to mastoiditis? What is a potential consequence of mastoiditis. How is it treated?
- Middle ear infections can spread to mastoid air cells
- Area suitable for pathogenic replication due to their porous nature
- Mastoid process can get infected and this can spread to middle cranial fossa, into the brain causing meningitis
- Pus must be drained from air cells and care taken not to damage facial nerve
What does auditory tube connect? WHat is its function? Why is it clinically significant?
Connects middle ear to the nasopharynx
Functions to equalise pressure of middle ear to that of external auditory meatus
pathway through which an upper RTI can spread into middle ear
What is glue ear?? Why does it occur? What is the result and how does it present?
- Otitis media with effusion
- Occurs due to persistent dysfunction of auditory tube. If auditory tube unable to equalise middle ear pressure (can be due to blockage, inflammation or genetic mutation), negative pressure develops in middle ear
- Negative pressure draws out transudate from mucosa of middle ear, creating an environment suitable for pathogens.
- Inspection of patient will reveal inverted eardrum with fluid visible inside the ear
What bone is the inner ear located in?
petrous part of temporal bone
What are the 2 main areas of the inner ear?
bone labyrinth and membranous labyrinth