9) Anatomy of the Ear Flashcards
What are the general functions of the ear?
Hearing and balance
What are the three parts of the ear?
External, middle and inner
What are some general symptoms that point towards the diagnosis of ear disease?
Otalgia (pain) Discharge Hearing loss Tinnitus Vertigo
In which bone is the ear found?
Petrous part of temporal bone
What is the function of the external ear?
Collects, transmits and focuses sound waves onto tympanic membrane
What does the external ear consist of?
Pinna, external auditory meatus and lateral surface of tympanic membrane
Describe the structures forming the pinna:
Outer rim: helix
Inner fold: antihelix
Inferior: lobule
Entrance to EAM: tragus, concha and antitragus
What is a pinna haematoma?
Blood collects between cartilage and perichondrium causing loss of blood supply to cartilage and pressure necrosis of tissue
What can cause a pinna haematoma?
Blunt injury to pinna
What is the treatment for a pinna haematoma?
Drainage and re-apposition of layers
What can occur if the external ear is repeatedly damaged?
Fibrosis and asymmetrical cartilage development = cauliflower ear
Describe the external acoustic meatus:
2.5cm long skin lined canal in a sigmoid shape (pull ear up and back when examining)
Cartilaginous laterally and bony medially
Where are hairs and wax found in the ear and what are their functions?
On cartilaginous portion
Prevent objects entering deeper canal and aids desquamation and skin migration out of canal
What is otitis externa?
Inflammation of external ear (swimmer’s ear)
Describe the tympanic membrane:
Fibrous CT structure that is pearly and translucent
What features can be seen on the tympanic membrane when examining the ear?
Outline of malleus stretching down in the middle
Attic
Pars tensa
Cone of light (points right in right ear)
How can the tympanic membrane be damaged?
Perforation due to infection, pressure or trauma
What is otitis media and how does it look on examination?
Acute middle ear infection
Red, bulging, featureless ear drum
What does the middle ear consist of?
Ossicles: malleus, incus and stapes
Tympanic cavity and epitympanic cavity (high)
What is the function of the ossicles?
Amplify vibration from tympanic membrane to cochlea via oval window
How are the middle ear and nasopharynx connected?
Why?
Eustachian tube - allows equilibration of pressure within middle ear cavity with atmosphere
What is otitis media with effusion?
Build up of fluid and negative pressure in middle ear as Eustachian tube is closed, so cells in middle ear absorb air
How does otitis media with effusion affect the ear, and hence how does it commonly present?
Decreases mobility of tympanic membrane and ossicles
Effects hearing and performance in school
What is the treatment for glue ear?
Spontaneous resolution or grommets - plastic ventilation tube through tympanic membrane
What are some complications of otitis media?
Tympanic membrane perforation
Facial nerve involvement
Mastoiditis or intracranial infections
What structures run close to the ear?
ICA, sigmoid sinus, mastoid cells, CN VII (chorda tympani) and VIII
What is mastoiditis?
Infection that spread to air cells of mastoid process
What is cholesteatoma?
Negative pressure draws ear drum inwards and leads to small pocket where skin cells collect and grow. Can erode structures
What causes cholesteatoma?
Chronic/recurring ear infections
Blockage of Eustachian tube
What does the inner ear consist of?
Cochlea, semicircular canals and vestibule (utricle and saccule)
Describe the features of the cochlea:
Bony and membranous labyrinth (cochlear duct)
Round and oval window
Describe how we hear:
Vibration of ossicles sets up vibrations in cochlear fluid (endolymph) -> sensed by nerve cells in cochlear duct (spiral organ of Corti) -> movement of these receptors trigger AP in CN VIII -> brain
Describe how the vestibular apparatus is involved in balance:
Fluid filled series of channels and sacs that respond to position rotation and maintain balance
What is conductive hearing loss?
From cochlea outwards, problem conducting sound
What is sensorineural hearing loss?
Problem with CN VIII or in cochlea
What is vertigo?
Dizziness with spinning sensation
What is Meniere’s disease?
Attacks of vertigo, hearing loss and tinnitus
What is Benign Paroxysmal Positional Vertigo?
Attacks of vertigo when move head in certain direction
What is Ramsay-Hunt Syndrome and how does it present?
Shingles in CN VII
Vesicles on pinna and facial nerve palsy
Describe the results of Weber’s and Rinne’s test for conductive hearing loss:
Sound towards affected ear
Bone conduction greater than air conduction in affected ear
Describe the results of Weber’s and Rinne’s test for sensorineural hearing loss:
Sound away from affected ear
Air conduction better than bone conduction but both bad
What can cause hyperacusis?
Damage to nerve to stapedius (CN VII)
