Ears Flashcards
What bone is the external acoustic meatus in?
Squamous part of temporal bone
What bone is the internal acoustic meatus in?
Petrous part of the temporal bone
What are the primordial origins of the temporal bone?
Mesoderm from first two branchial arches, occipital somites
What parts of the temporal bone form via intramembranous ossification?
Squamous and tympanic parts (from first pharyngeal arch)
How are the malleus and incus formed?
Endochondrally from first branchial arch cartilage
How are the stapes and styloid process formed?
Endochondrally from second branchial arch cartilage
How are the petrous temporal and mastoid processes formed?
Endochondrally from occipital somite cartilage
What is A?
Squamous part of temporal bone
What is B?
Articular eminence
What is C?
Mandibular fossa
What is D?
Zygomatic process
What is E?
Styloid process of the temporal bone
What is F?
Tympanic plate
What is G?
External auditory meatus
What is H?
Mastoid process of temporal bone
What is A?
External auditory meatus
What is B?
Tympanic membrane
What is C?
Middle ear cavity
What is D?
Auditory tube
What is E?
Cochlea
What is G?
Semicircular canal
What is H?
Ear ossicles
What primordia develops into the skin of the external auditory meatus and outer surface of tympanic membrane?
Ectoderm of the first branchial groove
What primordia gives rise to the cartilages of the auricle?
Condensations of pharyngeal arch 1 & 2 mesenchyme
What primordia gives rise to the auditory tube, middle ear cavity, aditus, mastoid antrum, mastoid air cells, and inner surface of tympanic membrane?
Endoderm of first pharyngeal pouch
What primordia gives rise to the cochlea and vestibular apparatus (semicircular canals) of the inner ear?
Ectoderm of the otic placode/otocyst
What are the parts of the ear drum?
Main part = pars tensa
Upper part = pars flaccida (more mobile)
What are the main features of the eardrum?
Handle of malleus
Umbo (central depression in the ear drum)
What is the function of the cochlea?
Hearing
What is the function of the semicircular canals?
Balance, equilibrium, and rotational motion
What is the sound wave conduction sequence?
Tympanic membrane –> malleus –> incus –> stapes –> oval window –> scala vestibuli perilymph –> cochlear endolymph fluid –> tectorial membrane in cochlear duct –> shearing forces on hair cell stereocilia –> cochlear nerve stimulation
What muscles dampen ossicle vibrations? What is their innervation?
Stapedius (facial nerve) and tensor tympani (trigeminal nerve)
How are hair cells in the utricle and saccule stimulated?
By calcium carbonate otoliths that exert force on hair cells by gravity or linear acceleration of the head in any direction
What is A?
Tensor Tympani
What is B?
Tegmen Tympani
What is C?
Malleus
What is D?
Incus
What is E?
To mastoid air cells
What is F?
Stapes
What is G?
Tympanic membrane
What is H?
Auditory tube
What is I?
Internal carotid artery
What is J?
Jugular bulb
What is K?
Facial nerve and chorda tympani
What is L?
Lesser petrosal nerve
What is M?
Lateral semicircular canal
What is N?
Promontory
What is O?
Round window
What is P?
Tympanic nerve (branch of IX)
What is the innervation of the external auditory meatus?
General sensory neurons in the vagus nerve (X)
What is the innervation of the inner ear?
Vestibulocochlear nerve (VIII) for hearing and balance (enters via internal acoustic meatus)
What is the innervation of the lining of the middle ear?
Tympanic branch of glossopharyngeal nerve
What is the innervation of the stapedius muscle of the middle ear?
Facial nerve (branchiomotor)
What is the function of the greater petrosal nerve?
Presynaptic parasympathetic fibers destined for lacrimal gland and mucosa of nasal cavity and palate
What is the function of the chorda tympani?
Taste fibers for the anterior 2/3 of the tongue, presynaptic parasympathetic fibers destined for submandibular and sublingual salivary glands (via lingual nerve and submandibular ganglion)
What are the two major branches of the facial nerve within the temporal bone?
Greater petrosal nerve and chorda tympani
What is the innervation of the tensor tympani muscle?
Mandibular nerve (branchiomotor)
What is the path of the facial nerve through the ear?
It passes behind the middle ear (from internal acoustic meatus) to exit the stylomastoid foramen
What is the path of the greater petrosal nerve?
It exits the petrous part of the temporal bone
What is the path of the chorda tympani?
It arches over the inside of the tympanic membrane to exit the petrotympanic fissure
An important consideration for the spread of infection is the fact that the middle ear cavity is both physically connected to and shares a common primordium in development with the:
a) mastoid air cells
b) superior and inferior petrosal sinuses
c) external auditory meatus
d) semicircular canals
e) carotid canal
a) mastoid air cells
A middle ear infection that disrupts the tympanic nerve and plexus could impair the nerve pathway for:
a) nasal mucous secretion
b) external acoustic meatus sensation
c) hearing
d) parotid salivary gland secretion
e) taste on the anterior two thirds of the tongue
d) parotid salivary gland secretion
The otic placode gives rise to the:
a) cochlea and semicircular canals
b) external auditory meatus
c) petrous part of the temporal bone
d) auricle (external ear)
e) lining of the middle ear cavity
a) cochlea and semicircular canals
A ruptured ear drum may damage the chorda tympani. What function might be impaired or lost?
a) balance
b) taste on the posterior 1/3 of the tongue
c) submandibular salivary gland secretion
d) middle ear sensation
e) mandibular protrusion
c) submandibular salivary gland secretion
A mass on the posterior wall of the middle ear cavity may damage what structure?
a) internal carotid artery
b) tympanic nerve
c) jugular bulb
d) facial nerve
e) vestibulocochlear nerve
d) facial nerve
If an insufficient number of mesenchymal cells migrate into the second pharyngeal arch, which part of the temporal bone may not develop properly?
a) styloid process
b) petrous part
c) squamous part
d) tympanic part
e) mastoid process
a) styloid process
The petrous part of the temporal bone is outlined by the superior and inferior petrosal sinuses. What do they drain?
a) subarachnoid space
b) sigmoid sinus
c) jugular bulb
d) sphenoid sinus
e) cavernous sinus
e) cavernous sinus
What is the structure of the external auditory canal?
It has a cartilaginous portion and bony portion. The cartilaginous portion has thicker skin and cerumen glands. The bony canal is part of the tympanic portion of the temporal bone.
What are the layers of the tympanic membrane?
Outer layer = squamous tissue
Middle layer = fibrous tissue
Inner layer = mucosal tissue
What is the general structure of the middle ear?
It is a sinus with a mucosal lining that has three middle ear bones
What are the three fluid filled spaces of the inner ear filled with?
Scala tympani and scala vestibule = perilymph
Scala media = endolymph
What is the difference between endolymph and perilymph?
Endolymph = high potassium and low sodium
Perilymph = low potassium and high sodium
What is a pure tone audiogram?
A test that directly tests a patient’s ability to hear through air and bone conduction (tests cochlear response to sounds)
What does the stapedius muscle do? What innervates it?
It attaches to stapes and contracts in response to loud sounds, chewing, speaking.
Innervated by facial nerve (VII)
What is the function of the tensor tympani?
Helps open eustacian tube
How does the ear overcome impedence from the fluid in the cochlea?
The area of the tympanic membrane to oval window is 20:1, lever action of ossicles amplifies sounds
What is the structure of the cochlea?
Each lobe of the cochlea has three compartments (top to bottom): Scala vestibuli, scala media, and scala tympani
What is the movement of the fluid wave through the cochlea?
Starts at oval window and scala vestibuli –> travels up to apex of cochlea –> continues back down through the scala tympani to the round window
What is the difference in frequency at different parts of the cochlea?
Base of cochlea = high frequency
Apex of cochlea = low frequency
What is the difference between outer and inner hair cells?
Different shapes (outer = V or W shaped, inner = straight line)
Outer = amplifies signals, Inner = sends signals to neurons
What types of movements does the saccule sense?
Up and down linear acceleration
What types of movements does the Utricle sense?
Horizontal linear acceleration
What are the two main types of hearing loss?
Conductive - sound is blocked on its way to the cochlea
Sensorineural - cochlea and/or auditory nerves aren’t working
What are the two types of hearing?
Air conduction, bone conduction
What is the Weber test?
Vibrating tuning fork placed on middle of forehead
- if normal, sound heard in both ears*
- if sensorineural hearing loss, sound lateralizes towards good ear*
- if conductive hearing loss, sound lateralizes toward bad ear*
What is a Rinne test?
What are the results of tuning fork ear testing for sensorineural hearing loss?
Positive Weber towards good ear
Positive Rinne (normal)
What are the results of tuning fork ear testing for conductive hearing loss?
Positive Weber test toward bad ear
Negative Rinne test (abnormal)
How do you read audiometry results?
Higher on chart = better, lower on chart is worse hearing
What does a type A tympanogram mean?
Normal (type As is stiffened eardrum)
What does a type B tympanogram mean?
Lack of conduction of sound through the eardrum (fluid/eustacian tube dysfunction or hole in TM)
What does a type C tympanogram mean?
It is due to negative pressure sucking ear drum in, tests eustacian tube function
What is speech testing?
A test for recognition of speach/words
What is the acoustic reflex test?
A test that measures the response of stapedius muscle to loud sound (it is supposed to contract in both ears when one is stimulated)
What are otoacoustic emissions tests?
Tests that measure the sounds given off by the inner ear when cochlea is stimulated by sounds. Absence of sound signifies block in air conduction or within cochlea.
What is ABR audiometry?
Auditory Brainstem Response test that creates waveform responses to test nerves/brain sites associated with hearing
What is microtia and aural atresia?
A congenital condition with a smaller than normal and/or deformed ear with absent ear canal. It has maximal conductive hearing loss and usually normal bone conduction.
What is cerumen?
Ear wax - contains lysozymes and other components to help fight infection. It is also slightly acidic and waterproof.
What are the most common etiologies of acute otitis externa?
Pseudomonas aeruginosa, enterobacteriaceae and vibrionaceae, staphylococcus, and coryneforms
What are ear canal osteomas and eostosis?
Bony growths in the ear. Osteomas are singular usually, exostosis are multiple and broader (associated with cold water exposure).
What is acquired external auditory canal stenosis?
A stenosis of the external canal that is usually acquired after infection and may require surgery.
What type of hearing loss is associated with tympanic membrane perforation?
Conductive hearing loss
What does the tympanic membrane look like if there is eustacian tube dysfunction?
Retraction because of lack of pressure equalization
What are the main pathogens associated with acute otitis media?
Strep pneumo, haemophilus influenzae, moraxella catarrhalis
What is the treatment for acute otitis media?
Oral antibiotics - penicillin based
What is serous otitis media?
Chronic otitis media with effusion that can form after resolved purulent otitis media and may cause conductive hearing loss and require a tube to drain
What are the major complications of acute otitis media?
Facial palsy, VI nerve palsy, coalescent mastoiditis with subperiosteal abscesses, intracranial complication (epidural, subdural, and brain abscesses), meningitis, sinus thrombosis
What is otosclerosis?
A genetic disorder (autosomal dominant) that causes progressive, low-frequency conductive hearing loss and an absent stapedial reflex
What is a cholesteatoma?
An epithelial skin cyst in the middle ear (either congenital or acquired) that can infiltrate into mastoid cavity or down eustacian tube and cause more damage and bony erosion. It must be removed completely or it will grow back
What is the most common cause of congenital sensorineural hearing loss?
Maternal CMV
What is the presentation and treatment for acoustic neuroma?
Presentation: asymmetric hearing loss and tinnitus, sudden
Treatment: observation, microsurgery
What is Meniere’s disease?
A disease characterized by episodic vertigo, fluxuating hearing loss, aural pressure, and tinnitus. Unknown cause.
What is the treatment for Meniere’s Disease?
Medical: low salt diet, diuretics, expectant treatment
Surgical: nerve section, labrinthectomy, gentamicin injection, decompression of endolymphatic sac
