The Ear Flashcards
What are the three parts of the ear?
External, middle and inner
Within which bone of the skull do we find parts of the ear?
Temporal bone (petrous part)
What does the external ear consist of?
Pinna, external auditory meatus and lateral surface of the tympanic membrane
What is the function of the external ear?
Collects, transmits and focuses sound waves onto the tympanic membrane
Where does blood accumulate in a pinna haematoma?
Between cartilage and perichondrium
What deformity does poorly treated pinna haematoma lead to?
Cauliflower deformity
What shape is the external acoustic meatus?
Sigmoid
What are the parts of the ear canal?
Cartilaginous (outer 1/3) and bony part (inner 2/3)
In which part of the ear canal are there hairs and wax production?
Cartilaginous part - outer part
How long is the external acoustic meatus?
2.5 cm
What does the middle ear consist of?
Ossicles (3 bones) and an air filled cavity
What are the ossicles in the middle ear?
Malleus, incus and stapes
What is the function of the middle ear?
Amplify and relay vibrations from the tympanic membrane to the inner ear (transmits vibration from an air medium to a fluid medium
What muscles tamper with the movement of the ossicles?
Stapedius and tensor tympani
Which nerve gives off the branched nerve to stapedius?
Facial nerve
When does stapedius contract?
If potentially excessive vibration due to loud noise
Why do patients with facial nerve damage sometimes present with hyperacousis?
Loss of nerve to stapedius -> stapedius does not contract to dampen vibrations reaching the inner ear
What is otosclerosis?
When the ossicles become fused at articulations so sound vibrations cannot be transmitted - causes deafness
What bone does the middle ear lie within?
Temporal
What are the mastoid air cells?
A collection of air-filled spaces in the mastoid process of the temporal bone
What does the eustachian tube do?
Equilises the pressure of the middle ear to that of the EAM
What is otitis media with effusion commonly known as?
Glue ear
What causes otitis media with effusion?
If the eustachian tube is unable to equalise middle ear pressure, a negative pressure develops inside the middle ear and draws out a transudate from the mucosa of the middle ear
How does the tympanic membrane appear in otitis media with effusion?
Retracted and straw coloured
What are some symptoms of acute otitis media?
Otalgia, temperature
Why are middle ear infections more common in children?
Eustachian tube is shorter and more horizontal in infacts so there is easier passage for infection from the nasopharynx to the middle ear
What are some complications of acute otitis media?
Tympanic membrane perforation, facial nerve involvement, mastoiditis, intracranial complications eg meningitis
What potentially life-threatening condition can mastoiditis cause?
Meningitis - spreads to the middle cranial fossa and into the brain
What is cholesteatoma?
Abnormal skin growth growing into the middle ear, behind the tympanic membrane
Causes painless, smelly otorrhea
What does the inner ear consist of?
Vestibular apparatus and cochlea
What does the cochlea do?
Converts vibration into an action potential which is perceived as sound
It is a fluid filled tube - waves of fluid cause movement of special sensory cells (stereocilia) within the cochlear duct which generate APs in CN VIII
What does the vestibuar apparatus do?
Maintains our sense of position and balance
Outline the mechanism behind hearing
1) Auricle and EAM focuses and funnels sound waves towards the tympanic membrane which vibrates
2) Vibration of the ossicles (stapes at the oval window) sets up movement in cochlear fluid
3) These movements are sensed by stereocilia in the cochlear duct
4) Trigger action potentials in cochlear part of CN VIII
5) Goes to primary auditory cortex to make sense of the input
What does the vestibular apparatus consist of?
Semicircular duct, the saccule and utricle (fluid filled series of channels and sacs that respond to position and rotation)
What are some diseases of the inner ear?
Meniere’s disease
Benign paroxysmal positional vertigo
Labrynthitis
What is the normal finding of a Rinne test?
Air conduction is greater than bone conduction
What is the normal finding of a Weber test?
Midline localisation
In sensorineural hearing loss, what is the finding in a Rinne test?
Air conduction is greater than bone conduction
In sensorineural hearing loss, what is the finding in a Weber test?
Localises to normal ear
In conductive hearing loss, what is the finding in a Rinne test?
Bone conduction is greater than air conduction
In conductive hearing loss, what is the finding in a Weber test?
Localises to affected ear
What does the pathology involve in conductive hearing loss?
Involving the external or middle ear
eg wax, otitis media, glue ear, otosclerosis
What does the pathology involve in sensorineural hearing loss?
Involving the inner ear or CN VIII
eg presbyacusis, meniere’s disease, acoustic neuroma, ototoxic medications
What is Meniere’s disease characterised by?
Episodes of vertigo, low pitched tinnitus and hearing loss
