12: Anatomy And Histo Of The Ear Flashcards
Where is the ear located?
In the dense petrous portion of the temporal bone
Two arteries to the external ear
- Posterior auricular A
2. Superficial temporal A
Two nerves that provide sensory to the external ear
- Greater auricular N
2. Auriculotemporal N
Two gland types in the external acoustic meatus
- Ceruminous glands
2. Sebaceous glands
Outside vs inside of TM histo
Outside: stratified squamous ep
Inside: simple cuboidal ep
Tip of cone shape on external TM
Umbo
N to external and internal TM
External: auriculotemporal N
Internal: small branch of CN V3
Two things that can cause perforated TM
- Abnormal increase in medial ear pressure
2. External trauma
Two parts of the middle ear
- Tympanic cavity
2. Epitympanic recess
Six walls of the middle ear
- Tegmental wall
- Jugular wall
- Membranous wall
- Labyrinthine wall
- Mastoid wall
- Carotid wall
Pharyngotympanic tube
Connects middle ear to nasopharynx
Pharyngotympanic tube composition
Posterolateral part is bon, remainder is elastic cartilage
Three muscles that open the pharyngotympanic tube
- Levator veli palatini
- Tensor veli palatini
- Salpingopharyngeus
Incus location and connection to wall
- In epitympanic space
2. Connected to posterior wall by a ligament
How much do the auditory ossicles amplify vibratory force?
10x
Tensor tympani O and I
O: pharyngotympanic tube, greater wing of sphenoid, petrous part of temporal bone
I: malleolus
Tensor tympani action
Pulls malleolus to tense membrane, reducing amplitude
Innervation to tensor tympani muscle and stapedius muscle
Tensor tympani: CN 5
Stapedius: CN 7
Stapedius O and I
O; pyramidal eminence on posterior wall of tympanic cavity
I: stapes
Stapedius action
Pulls stapes posteriorly, reducing oscillatory range, preventing excess movement of stapes
Otitis media
Earache with possible fluid or pus in middle ear due to inflammation or infection
Mastoiditis
Infection of mastoid cells, treated with Abx
Where can mastoiditis spread to
Into cranial fossa via petrosquamous cranial suture
Three areas in the bony labyrinth
- Semicircular canals
- Vestibule
- Cochlea
What does the vestibule contain?
Saccule, utricle
Where is the membranous labyrinth
Inside the bony labyrinth
Three divisions of the membranous labyrinth
- Vestibular division (semicircular ducts, utricle, saccule)
- Cochlear division
- Sensory cells
Six regions of sensory cells
1 organ of corti
2 maculae
3 cristae ampullari
Perilymphatic space
Between bony and membranous labyrinths
Liquid in perilymphatic space and what it drains via into where
Similar to CSF
Drains via perilymphatic duct -> into subarachnoid space
Endolymphatic space fluid - composition and where it comes from
High in K, low in NA
Originates from stria vascularis
Where does endolymphatic fluid drain into and via what?
Endolymphatic duct -> venous sinuses of dura mater
Hair cell composition (vestibular vs auditory system)
Have an array of stereocilia
In vestibular system: has one true Cilium (kinocilium)
In auditory system: cilia structure is lost besides kinocilium’s basal body
Gates in stereocilia
Mechanoelectrically-gated ion channels, that allow K to enter when moved
What does gentamicin target?
Hair cells
Three compartments of the cochlear duct
- Scala media
- Scala vestibuli
- Scala tympani
Fluid in scala media vs scala vestibuli
Media: endolymph
Vestibuli: perilymph
Stria vascularis
Lateral wall of scala media, produces endolymph and contains the organ of corti
Which two compartments of the cochlear duct are continuous?
Scala vestibuli, scala tympani
Three types of cells in the organ of corti and their function
- Hair cells: sensory
- Phalangeal cells: support
- Pillar cells: support
Where are hair cell stereocilia embedded in the organ of corti?
In the overlying tectorial membrane
Sound moving through the organ of corti
Basilar membrane vibrates -> stereocilia deflection -> K channels open in hair cells -> moves tectorial membrane -> signals bipolar neuron cells bodies in spiral ganglion
How does the spiral ganglion transmit signals?
Via CN 8
Where is scala vestibuli moved?
By the stapes at the oval window
Which part of the cochlear duct connects to the round window?
Scala tympani
Outer spiral lamina
Bony shelf that supports the tectorial membrane
High vs low frequency in cochlea
High: detected near base of cochlea
Low freq: move further, closer to the tip of the duct
What is changed depending on amplitude of sound
Degree of displacement of hair cells
Three types of hearing loss with what is affected
- Conductive: outer/middle ear
- Sensorineural: inner ear or auditory nerve
- Central: CNS
Examples of things that can cause conductive hearing loss
Fluid buildup in middle ear, otitis, excess ear wax, otosclerosis (stiff ear bones)
What causes sensorineural hearing loss?
Age and noise
Describe the semicircular canals
Three canals in different axes, filled with endolymph
Ends of semicircular canals
Ampulla: filled with gelatinous material with a cupula, sensory hair cells have stereocilia attached to cupula, which becomes displaced by motion in the canals
What do the semicircular canals detect?
Rotational velocity
What do the utricle and saccule both contain?
A macula
What is in a macula
Cluster of hair cells with stereocilia embedded in otolithic membrane, which is covered in otoconia
Otoconia
Ca carbonate crystals in the maculae
What two things do the utricle and saccule sense
Gravity, linear acceleration
Menieres cause
Increase endolymph volume -> abnormal signaling (true cause is unclear)
Possible treatment for severe Menieres
Surgical ablation of parts of labyrinthine system, but risks of permanent hearing loss
Sx of menieres syndrome
Dizziness, vertigo, tinnitus, fluctuating hearing loss
Viral labyrinthitis
Same symptoms as Menieres, but usually resolves in a week
Three nerves in the internal acoustic meatus
- Vestibular N
- Acoustic N
- Facial N
