Ear Flashcards
Does CN VIII ever exit the skull?
No
What nerve is given off anteriorly off of the facial nerve at the genu?
-Greater petrosal nerve
**contains parasympathetics
Where does the largest portion of the facial nerve exit the skull?
Stylomastoid foramen
What is the opening from the middle ear to the mastoid air cells?
Aditus ad antrum
What is the smallest striated muscle in the human?
-stapedius
**when patients complain about things being too loud, worry about this & facial nerve
What innervates stapedius?
Facial nerve
What innervates Tensor Tympani?
Trigeminal (V3)
What fibers are contained within the lesser petrosal nerve?
-parasympathetic fibers of CN IX
What fibers are contained within the greater petrosal nerve?
-Parasympathetic fibers of CN VII
What nerve supplies sensory information from the superior portion of the external ear?
Auriculotemporal (branch of V3)
What nerve supplies sensory information from the inferior portion of the external ear?
Greater auricular nerve (C2-C3)
At what frequency do humans hear best? Why?
4000 Hz
- Due to resonance frequency of outer ear
- babies like higher pitched noises due to shorter ear canal, can discriminate higher pitches better
What is acoustic impedence?
- resistance to sound wave conduction
- Air = low, water = high
What are the three ways that we are able to localize sound in space?
- interaural time difference
- interaural intensity difference (head shadow)
- head transfer function (effect of shape of ear, frequency of sound changes depending on where it hits our pinna)
What is a monolaminar membrane?
-if there is a large enough perforation, fibrous layer of tympanic membrane doesn’t form back, and hole is sealed by epithelium and endothelium only
What is a Cholesteatoma?
- A collection of dead desquaminated skin cells that most likely forms in a retraction pocket
- retraction pocket forms when you have a monolaminar membrane and poor eustachian tubes, leading to negative pressure inside ear
What is the acoustic stapedial reflex (ASR)?
- If you hear a sound more than 80 dB, you get an instant (10 uS) contraction of the stapes by the stapedius
- will drop the amplitude of low frequency (<2000 Hz) sounds
**think about implications of CN VII paralysis
What is the prevocalization reflex?
- When you are preparing to speak, you send information to tensor tympani and stapedius to contract so you don’t deafen yourself by speaking
- this is why our voice sounds different in our own head
What is the purpose of the eustachian tube?
- Prevent vacuum forming in middle ear
- drainage
What are myringosclerosis and tympanosclerosis?
- Calcium deposition on the tympanic membrane (Myringosclerosis)
- Ca deposition on ossicles (tympanosclerosis)
DIFFERENCE: Myringosclerosis does not cause symptoms, tympanosclerosis does.
What is otosclerosis?
There is a growth of bone that obliterates the stapes foot plate causing hearing loss
What is the difference between perilymph and endolymph?
- perilymph is pretty much CSF
- elvelopes the membranous labyrinth
- endolymph is synthesized at the stria vascularis of the cochlea
- higher in potassium
What are the three compartments of the cochlea? What membranes separate them?
- Scala vestibuli
- Reissner’s Membrane*
- Scala media (endolymph)
- Basilar Membrane*
- Scala tympani
What frequencies are resonant at the apex vs the base of the cochlea?
Apex: low frequency
Base: High frequency
What is the organ of corti?
- the area of the cochlea where hair cells are located
- tectorial membrane is above it
What is the functional difference between inner and outer hair cells?
- Inner hair cells transmit signal to brain
- outer hair cells alter vibration of basilar membrane to fine tune the amplification of sound
What does the stria vascularis do?
-produces endolymph
What do hair cells in the utricle respond to?
Horizontal acceleration of body
What do hair cells in the saccule?
Vertical accelerations of the body
What is Benign Paroxysmal Positional Vertigo (BPPV)?
- Most common cause of vertigo
- displaced otoconia causing local distortion of fluid mechanics
- just think, ear crystals
What is superior canal dehiscence syndrome?
- enhanced intracranial sound perception
- dizziness after hearing loud sounds and pressure changes
What is vestibular neuritis?
- acute unilateral vestibular deficit
- presumably due to viral induced inflammation
- probably from varicella zoster virus
What is Meniere’s Disease?
- metabolic disorder of inner ear homeostasis resulting in hearing loss and vertigo
- caused by increased pressure within the membranous labyrinth, rupture, and leakage into the perilymph
What three layers make up the tympanic membrane?
Cutaneous
Fibrous
Mucosal
Why is the distal end of the incus always the first place to get all fucked up?
-it has a poor blood supply
What muscle does the prevocalization reflex involve?
Tensor Tympani (V3)
Outer hair cells are bound to the ________ above them.
Tectorial membrane
What is Presbyacusis
-loss of high frequency hearing before low frequency hearing
What nerve carries the pain of otitis media?
CN IX
What is the roof of the middle ear cavity called?
Tegmen Tympani
What kind of ganglion is the geniculate ganglion?
Sensory!
