The Ear Flashcards
What structures make up the external ear?
Auricle and external acoustic meatus
What structures are within the inner ear?
Malleus, incus and stapes
What structures are within the inner ear?
Vestibule, cochlea
Where is the ear located?
Within the dense petrous portion of the temporal bone
What is the auricle of the external ear composed of?
Integument covered and elastic cartilage
What is the concha of the auricle?
Deep depression found in the auricle
What is the blood supply to the external ear?
Posterior auricular and superficial temporal
What part of the external ear does not have cartilage?
Lobule
What provides sensory innervation to the external ear?
Greater auricular nerve and auriculotemporal nerve
Describe the external acoustic meatus
Canal leading to the TM
Contains ceruminous glands (make wax) and sebaceous glands in the integument
Cartilage beneath supports the outer portion of the canal
Describe the tympanic membrane
Semi transparent membrane
Outside layer lined with stratified squamous epithelium
Inside layer lined with simple cuboidal epithelium
Moves with sound and transmits to ossicles
What is the innervation to the TM?
External surface by auriculotemporal N
Inner surface by small branch of V3 and by small auricular branch of vagus nerve
What is the shape of the TM?
Cone shaped with the tip (the umbo) oriented toward the external acoustic meatus
Perforated TM is often due to what?
Abnormal increase in medial ear pressure because of fluid or barotrauma
External trauma
How is perforated tympanic treated?
Most heal but may need follow up with Abx (avoid gentamicin bc it can damage hair cells)
What are the two parts of the middle ear (tympanic cavity)?
Tympanic cavity proper and epitympanic recess
What wall is the roof of the middle ear?
Tegmental wall
What wall is the floor of the middle ear?
Jugular wall
What forms the lateral wall of the middle ear?
Membranous wall
What forms the medial wall of the middle ear?
Labyrinthe wall
What forms the posterior wall of the middle ear?
Mastoid wall
What forms the anterior wall of the middle ear?
Carotid wall - near opening of pharyngotympanic tube and canal for tensor tympani
Describe the pharyngotympanic (Eustachian) tube
Connects TM with nasopharynx
Posterior lateral part is bone but remainder is cartilaginous (elastic)
Functions to equalize pressures
What opens the pharyngotympanic tube?
Levator veli palatine, tensor veli palatine and salpingopharyngeus muscles
The auditory ossicles run from the TM to what?
The oval window of the cochlea
What does the malleus articulate with?
Incus
Also connected to the TM
Describe the incus
Has body and two processes
Body lies in epitympanic space
Articulates with head of malleus
Short process is connected to posterior wall by ligament
Describe the stapes
Has head, two limbs and base
Head articulates with the incus
Base attached to oval window and is very small so vibratory force from TM gets amplified almost 10x
What is the origin and insertion of the tensor tympani muscle?
Origin: surface of pharyngotympanic tube, greater sphenoid wing and petrous part of the temporal bone
Insertion: handle of malleus
What innervates the tensor tympani muscle?
CN V
What is the action of tensor tympani muscle?
Pulls on handle of malleus to tense membrane and reduce amplitude
What is the origin and insertion of the stapedius muscle?
Origin: within pyramidal eminence (hollow cone shaped eminence on posterior wall of tympanic cavity)
Insertion: tendon exits via small pinhole sized foramen and inserts onto stapes
What innervates the stapedius muscle?
CN VII
What is the action of the stapedius muscle?
Pulls stapes posteriorly tightening annular ligament attaching it to the widow
Reduces oscillatory range and prevents excessive movement of stapes
What is otitis media?
Ear-ache with possible fluid or pus in the middle ear due to inflammation or infection
TM appears red and bulged
Fluid may be visible through membrane
If left untreated can impair hearing and scarring of auditory ossicles
What is mastoiditis?
Infection of mastoid air cells
Can spread into cranial fossa via petrosquamous cranial suture
Treated with Abx
What is the bony labyrinth of the inner ear?
Interconnected cavities and canals within bone
Contains semicircular canals, vestibule (space containing saccule and utricle) and cochlea
What is the membranous labyrinth of the inner ear?
Lies within bony labyrinth and consists of small sacs and tubules forming continuous spaces enclosed by an epithelium Vestibular division (semicircular ducts, utricle and saccule) and cochlear division
Describe the sensory cells found within the membranous labyrinth of the inner ear
Found in 6 regions (3 cristae ampullaris, 2 maculae and one organ of corti)
Hair cells and support cells
Mechanosensory cells: convert mechanical energy into electrical energy transmitted via CN VIII to brain
Describe perilymph
Found within the perilymphatic space between bony and membranous labyrinths
Composition similar to CSF
Drains via perilymphatic duct (cochlear aqueduct) into subarachnoid space
Describe endolymph
Found within the endolymphatic space within the membranous labyrinth
High in K and low in Na
Originates from stria vascularis
Drains via endolymphatic duct into venous sinuses of dura mater
Describe hair cells
Surface contains rows of stereocilia that increase in height along a particular direction
Vestibular system contains one true cilia (kinocilium) located behind tallest stereocilia
In the auditory system lose the cilia structure but retain its basal body
Describe stereocilia
Stiff and contain mechanoelectrically gated ion channels
If deflected toward the tallest one, K channels opens
Close if in opposite direction
Hair cells are innervated by what?
Both efferent (modulate sensitivity) and afferent nerves
Hair cells are a target of what?
Ototoxicity effects by Abx
Can destroy hair cells
What is the cochlear canal?
Spiral space within bone containing the cochlear duct
What is the cochlear duct?
Divides the cochlear canal into 3 parallel soft tissue lined compartments
Scala media, scala tympani and scala vestibuli
What is the scala media?
Middle compartment of the cochlear duct
Contains endolymph
Stria vascularis: lateral wall of scala media and source of endolymph
What is the scala vestibuli?
Contains perilymph and fluid is moved by stapes at oval window
Continuous with scala tympani
What is the scala tympani connected to?
The round window
What is the organ of corti?
On floor of scala media resting on basilar membrane
Composed of hair cells, inner and outer phalangeal cells (support for hair cells), and pillar cells (support between basilar membrane and tympanic lip)
What is the osseous spiral lamina?
Inner spiraling bony shelf serving as support for tectorial membrane and spiral ganglia (contains bipolar neuron cell bodies)
Describe the structure of the organ of Corti
Three rows of outer hair cells and single row of inner hair cells
Hair cell stereocilia are embedded in overlying tectorial membrane extending from the spiral lamina
The basilar membrane vibrates with sound causing what?
Deflection of stereocilia attached to tectorial membrane, opening K channels in hair cells
What is the path of sound waves?
Stapes moves oval window causing fluid pressure wave formation in perilymph
Waves distorts vestibular membrane causing a pressure wave within endolymph of the scala media
This displaces basilar membrane and distorts stereocilia of hair cells
Pressure in perilymph is transferred to scala tympani and exits via round window
What is conductive hearing loss?
Effects outer or middle ear
Fluid build up in the middle ear, otitis, excessive wax, osteoscleosis
What is sensorineural hearing loss?
Reduction in sound level and/or fidelity due to damage to inner ear or auditory nerve
Affects hearing at different frequencies and intensities
Age related and noise induced
What is central hearing loss?
Problem in the CNS
Describe semicircular canals and ampulla
Three canals in three different axes
Endolymph filled and connected to utricle
End of canals have ampulla with gelatinous like cap called a cupulla
Sensory hair cells with stereocilia are attached to the cupulla
Cupulla is displaced by fluid motion within canal
Serve as sensors of rotational velocity
The vestibule contains a saccule and utricle which each contain a macula comprised of what?
A cluster of hair cells with stereocilia with overlying gelatinous material called otolithic membrane
Otolithic membrane covered with Ca carbonate/protein crystals called otoconia
What is the function of the macula of the utricle and saccule?
Serve as sensors for gravity and linear acceleration
What two diseases are associated with the membranous labyrinth?
Ménière’s syndrome and viral labyrinthitis
What is Ménière’s syndrome?
Experience dizziness, vertigo, high pitched rushing or roaring sound (tinnitus) and fluctuating hearing loss
Associated with increase endolymph volume leading to abnormal signaling
Cause is unclear
Mild cases are treated with medication
Severe cases require surgical ablation of parts of labyrinthine system but there are risks of permanent hearing loss
What is viral labyrinthitis?
Similar sx to Ménière’s syndrome
Usually resolves within a week
High frequency sounds are detected where?
Near the base of the cochlea while low frequency sounds are detected closer to the tip of the cochlear duct
