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
What is contained within the bony labyrinth. What is it lined internally by and what is the name of the fluid?
Contains cochlea, vestibule, and 3 semicircular canals. All are lined internally with periosteum and contain a fluid called perilymph
What is contained within the membranous labyrinth? Where is it found? What is it lined internally by and what is the name of the fluid?
Found inside bony labyrinth. Consists of cochlear duct, semicircular ducts, utricle, and the saccule. Filled with fluid called endolymph.
What are the 2 parts contained inside the vestibule of the bony labyrinth?
Saccule and uticle
What is contained inside the cochlea of the bony labyrinth? How is the shape formed?
Twists upon itself around a central portion of bone called the modiolus, producing a cone shape which points in an anterolateral direction
What nerve is found at the base of the modiolus?
What are the 3 semicircular canals found in the bony labyrinth? WHat is their function? WHat is the swelling at one end known as?
- anterior, lateral, posterior
- Contain semicircular ducts which are responsible for balance
- Each contains a swelling at one end known as the ampulla.
What are the ducts of membranous labyrinth filled with?
filled with endolymph
What is the function of the cochlear duct?
organ of hearing
What are the borders of the cochlear duct: laterally, roof and floor?
- Laterally – Spiral ligament
- Roof – Reissner’s membrane
- Floor – Basilar membrane (houses the cells of hearing – the organ of corti)
How is the cochlear duct held in place?
What are the saccule and utricle? What is their function?
Membranous sacs in vestibule
Provides information about head position when not moving
What is the function of the semicircular ducts of the membranous labyrinth and how do they work?
Upon movement of the head, flow of endolymph within ducts changes speed and/or direction. Sensory receptors in ampullae detect this change and send signals to the brain, allowing for processing of balance
What is menieres disease? How is it caused?
- Disorder of inner ear – episodes of vertigo, tinnitus and hearing loss
- Caused by excess accumulation of endolymph, causing progressive distension of the ducts. Resulting pressure fluctuations damages the thin membranes of the ear that detect balance and sound.
Describe the innervation of the inner ear. How does it enter the inner ear? Which never passes through inner ear without innervating anything?
- Innervated by vestibulocochlear nerve – enters inner ear via internal acoustic meatus and divides into vestibular nerve (balance) and cochlear nerve (hearing)
- Vestibular nerve – enlarges to form vestibular ganglion and then splits to supply utricle, saccule and 3 semicircular ducts
- Cochlear nerve – enters at base of modiolus and supplies the organ of corti
- Facial nerve passes through inner ear but not does not innervate anything.
What 3 branches of the facial nerve are given off in the petrous temporal bone?
- greater petrosal nerve
- nereve to stapedius
- chorda tympani
How does swallowing allow equalisation of pressure?
opens up eustachian tube allowing equalisation of pressure from middle ear to outside
Explain glue ear
middle ear cannot equalise with atmosphere as eustachian tube does not open properly
Mucous membrane continuously absorbs air in middle air and creates negative pressure
Fluid accumulates and pathogens grow