Ears Flashcards
Describe the structure of the external ear
- where are the boundaries
- what would you look for in an ear exam?
Pinna => external acoustic meatus => tympanic membrane
Pinna
- Helix, antihelix
- Superior, inferior crus
- Tragus, antitragus
- Concha
- Lobule
Tympanic membrane
- Pars flaccida above lateral process of malleus
- Pars tensa posterior to light reflex
Look for
-retracted/debris in pars flaccida => cholesteatoma => progressive ossicle damage, damage facial nerve, hearing loss, brain abscess, meningitis
Describe the route of the facial nerve
-why is this important in an ear exam?
Exits via stylomastoid foramen (posterior to external acoustic meatus and styloid process)
Branches
- temporal
- zygomatic
- buccal
- mandibular
- cervical
Describe the boundaries of the middle ear
- roof
- floor
- lateral wall
- medial wall
- anterior wall
- posterior wall
What cavities make up the middle ear
Roof => tegmen tympani (petrous)
-separates middle ear from middle cranial fossa
Floor => jugular wall
-separates middle ear from int jugular vein
Lateral wall => tympanic membrane, lateral wall of epitympanic recess
Medial wall => lateral wall of inner ear
Anterior wall => bony plate with opening for auditory tube, tensor tympani
-separates middle ear from ICA
Posterior wall => mastoid wall
- separates tympanic cavity and mastoid air cells
- hole allows for 2 areas to communicate
Tympanic cavity (3 ossicles) Epitympanic cavity
What are the 2 muscles found in the middle ear
-describe the innervation, attachments and function
Tensor tympani
- Tensor tympanic branch of V3
- auditory tubes <=> malleus
Stapedius
-Facial nerve, attaches to stapes
Contract in response to loud noise => reduced vibrations, transmission to inner ear for protection (acoustic reflex)
What is the clinical significance of the
- tensor tympani
- stapedius
Tensor tympani
- tinnitus => hyperactive contractions increase vibrations
- hyperacusis => flaccid paralysis
Stapedius
-acoustic neuroma => benign tumour on VII, VIII, can compress structures
Describe the differences in auditory tubes in children and adults
-what is its function
-
Cartilaginous bony tube that connects middle ear to nasal pharynx
Equalise pressures in ear and atmosphere
Allows for drainage of the ME
Children => shorter, straighter, narrower => otitis media more common
What is the function of the oval and round window
Oval window
-membrane covered opening that transmits vibrations from stapes to the cochlea
Round window
-membrane covered opening that allows for the movement of fluid in the cochlea
What is the function of the internal ear Describe the structure of the bony labyrinth -bony labyrinth -cochlea -Semicircular canals
Middle ear mechanical signals => inner ear electrical signals
Maintain balance by detecting position and motion
Filled with endolymph
Bony labyrinth => in petrous part
Vestibule
-separated from ME via oval window
-communicates with cochlea and semicircular canals
-saccule and utricle found here (responsible for balance)
Cochlea
- cochlea duct of membranous labyrinth
- twists around central modiolus (branches of VIII found here)
- cochlear duct in between vestibular and tympanic canal
Vestibular canal => continuous with vestibule
Tympanic canal => terminates at round window
Semicircular canals (responsible for balance) -semicircular ducts found here
Describe the structure and function of the membranous labyrinth
Continuous duct system filled with endolymph
Cochlea duct
- triangular duct between vestibular and tympanic canals
- basilar membrane houses Organ of Corti
Saccule, utricle
- 2 membranous sacs in vestibule, organs of balance
- utricle <= 3 semicircular ducts
- saccule <= globular in shape, receives cochlea duct
Semicircular duct
-organs of balance
Describe the 2 types of deafness
Describe the 2 hearing tests that could be used to differentiate between the 2
Conduction deafness => problem in transferring sound waves
Sensorineural deafness => inner ear, sensory organ issues
Weber => tuning fork on forehead
- sensorineural => sound louder in unaffected ear
- conductive => sound louder in affected ear
Rinne => tuning fork on mastoid process and move infront of EAM
- sensorineural =>air conduction > bone conduction
- conductive => bone conduction > air conduction
Why do foreign objects in the EAM sometimes cause coughing, vomiting
Vagus sensory innervates EAM
Vagus also triggers cough reflex
How can otitis media present
Who is most likely to present
-describe the pathophysiology
-what are the complications
Child presents with
- ear pain, tugging at lobule
- history of recent infection
- anteriorly displaced ear
- abscess behind pinna
Infection builds up in ME, needs to go somewhere
- hard to drain via auditory tube
- ear drum rupture
- spreads into mastoid air cells
May lead to
- mastoiditis
- bacterial meningitis
- brain abscess
- dural sinus thrombosis
