Vestibular System II Flashcards
What are the parts of the tympanic membrane?
Two parts, each bordered by the external acoustic meatus and teh tympanic cavity
1. Pars Tensa:
- Three layers:
Skin
Collagen fibers
Mucosa
2. Pars Flaccida
- Two layers:
Skin
Mucosa
What causes conductive hearing loss?
Perforation of the tympanic membrane or occlusion of the middle ear (often by ear wax)
What are the symptoms of conductive hearing loss?
Sound stimulus is not transmitted to the inner ear, therefore, patients present with:
- Hearing loss in affected ear
- Conductive sounds appear louder in affected ear
What are the parts of the middle ear?
What are possible complications of otitis media?
Temporal lobe abcess
Sigmoid sinus thrombosis
Mastoiditis (in mastoid air cells)
Facial Palsy
Labyrinthintis
Meningitis
ICA Thrombosis
IJV Thrombosis
What is the purpose of the receptors in the inner ear?
Respond to movements of the head
For audition
They are mechanoreceptors in specialized epithelium
What are the structures of the inner ear?
- Bony Labyrinth
- Semicircular Canals
(Anterior/Superior, Posterior, Lateral) - Vestibule
- Cochlea
- Membranous Labyrinth
- Filled with Endolymph
- Contains sensory receptors
- 4 parts
What is the function of the endolymphatic duct and sac?
Reabsorption of endolymph
- Only part of the inner ear, membranous labyrinth not covered in specialized epithelium
- Sac is extraosseous part and is positioned by sigmoid sinus to reabsorb endolymph and release it into blood stream
What is Meniere’s Disease?
Too much endolymph
Symptoms:
- Vestibular:
Dizziness/vertigo - Cochlear:
hearing loss
Where is the crista ampularis and what is its function?
Found in the ampulla of semicircular canals, fixed, while the endolymph in the canals is able to move.
- Contains:
Sensory Hair cells (2 types)
Supporting cells
Cupula
Function is to detect angular movement
What are the 2 types of Hair cells?
How does the crista ampularis detect movements of the head?
Movement of stereocillia and kinocillium towards cilium leads to depolarization
Movement of stereocillia and kinocillium away from cilium leads to hyperpolarization
Where is the macula found and what is its function?
Found in the utricle and saccule, the macule is used to detect Gravity and Linear acceleration
What are otoconia made of?
Calcium carbonate
(they are Ca-carbonate crystals)
What is the modiolus?
Found in the inner ear, it is a spiral shaped axis of the cochlea
- made of spongy bone, the cochlea turns approx 2.5x around it
- Spiral ganglion resides here
What is found in the cochlea?
Modiolus
Scala vestibuli (filled with perilymph)
Cochlear duct (filled with endolymph)
Scala tympani (filled with perilymph)
Organ of corti resides on the boundary between cochlear duct and scala tympani
What is the organ of corti? What is it made of?
Found in the cochlear duct, it is a sound receptor containing:
Inner hair cells - few in #
Outer hair cells - many in #
Supporting Pillar cells (Inner and outer)
Phalangeal cells
Tectorial membrane
base of basilar membrane = high frequencies
apex of basilar membrane = low frequencies
What is the shape of a “pure tone”?
Sinusoidal sound pressure wave of equal states of compression and rarefaction
–> localized pressure disturbances propagate away from sound source
How is a decibel calculated?
What is the process of hearing?
- Capture mechanical energy from the air (External ear)
- Conduct sound to receptors (Middle ear)
- Change mechanical vibrations into action potential firing patterns in an afferent nerve (Inner ear)
- Transmit neural signal to auditory centers of brain (Ascending auditory pathway)
- Perceive sound (cerebral cortex)
What are sound parameters?
Loudness - related to amplitude
Pitch - related to frequency
Timbre - related to shape of waveform
Location
What affects detection threshold of sound pressure?
Why are the ossicles of the middle ear necessary?
How does attenuation of ossicle movement occur?
Why is this important?
Muscles of the middle ear (tensor tympani and stapedius) contract in response to loud noises (>80dB) being most sensitive to lower frequencies
Response latency is too slow to protect from impulsive sounds
Purpose is to most likely reduce noise during vocalization
What is the process of cochlear nerve activation in the organ of corti?
Sound waves move the basilar membrane of the cochlea
–> tectorial membrane is more stiff and doesn’t move, causeing sheer forces on kinocilia and stereocilia
–> Increased NT released from hair cells
–> Increased AP firing in cochlear nerve afferent fibers occurs
What is the Place Theory?
The theory that frequency tuning of basilar membranes leads to spatial separation of auditory signal based on frequency (tonotopic organization)
Example:
A 10kHz sound causes max displacement near the base of the helicotrema, while a 0.5kHz sound causes max displacement near the apex
–> these signals remain separated throughout the auditory pathway
When does the Place Theory break down?
Place Theory doesn’t work at the low end of audible frequency range
–> The frequency map of basilar membrane ends at about 200Hz at Apex of the membrane
What is the function of the Stria Vascularis?
To produce endolymph
–> epithelium with blood vessels in it found in the cochlear duct
What is tinnitus?
ringing in the ears
What is conductive hearing loss?
What are the test results that identify it?
Defects in conductive mechanisms in external or middle ear
- Weber’s test of conductie hearing (tuning fork on forehead): sound lateralized to bad ear
- Rhinne test (tuning fork applied to mastoid process then in front of ear): sound is louder on mastoid process
What is Sensorineural hearing loss?
What are the test results that identify it?
Damage to cochlea, cochlear nerve, or cochlear nuclei
Weber’s test (tuning fork placed on forehead): sound lateralized to good ear
Rhinne test (tuning fork on mastoid process then in front of ear): sound is louder by air conduction, but more energy is needed to hear the sound
What are causes of Conductive hearing loss?
otosclerosis
middle ear infection
perforation of tympanic membrane
What are some causes of sensorineural hearing loss?
Meniere’s disease (build up of endolymph)
Noise trauma
Inner ear infection
Drug treatments
Age
Acoustic neuroma
What is audiometry?
testing of hearing loss by detecting threshold of hearing for specific sound frequencies
–> detection threshold is compared to normal threshold for each frequency to determine if hearing loss exists
What is an audiogram?
plots of hearing loss (difference between subject’s detection threshold and “normal” threshold) as a function of frequency
- determined by audiometry
