Hearing And Balance Flashcards
What are the three main components of the temporal bone?
Petrous - interior ridge containing the middle ear
Mastoid - auricular muscle attachment, many foramina to allow things to pass through, composed of air cells that can be repositories for infection
Squama Temporalis - thin and transparent, place where the Temporalis muscle attaches
Where are the mechanoreceptors that transducer fluid movements induced by sounds and head movement?
The inner ear within the petrous part of the temporal bone
What is a major repository for infections in the temporal bone?
The air cells that compose the mastoid of the temporal bone
How is sound intensity measured?
In decibels
What is the equation for calculating decibels?
dB = 20*log(P/P0)
What is dB SPL?
Same reference for all frequencies
Relative to 2x10^-5 N/m2
What Is dB HL (SL)?
Relative to the lowest sound pressure detected by individuals
Different reference level for each frequency
What is linearity?
What you put in is what you get out
What system is the middle eye?
A linear system
If you put in two frequencies you get two out
What type of system is the cochlea?
Nonlinear
If you out in two frequencies you get out multiple ones out, the ones different from your input and distortion products
How does (asymmetric) cauliflower ear happen?
Shearing to the anterior auricle causes it to separate from the elastic cartilage and tears the blood vessels
The subsequent hematoma stimulate cartilage growth
What are the four sensory nerves to the external ear?
Greater auricular (c2,3)
Lesser occipital
Auricular branch of the vagus nerve
Auriculartemporal branch of the mandibular nerve (V3)
Stimulation of what nerve can evoke then vago-vagal reflex resulting in fainting?
The auricular branch of the vagus nerve
What nerves innervate the tympanic membrane?
Auricular temporal of V (trigeminal)
Auricular branch of X (vagus)
Tympanic branch of IX (Glossopharyngeal)
What does vibration of the tympanic membrane do?
Cause the malleus and incus to pivot resulting in the stapes footplate vibration at the oval window
GAIN of pressure results in air conduction being better than bone conduction
Around how many decibels are lost due to conductive hearing loss because of sound reflection?
40-55dB
How is energy loss minimized in hearing conduction?
By impedance matching by the ossicles and tympanic membrane
What are the three aspects of the middle ear that minimize energy loss of sound?
- Areal ratio - the area of the tympanic membrane is much larger than the round window
- Lever ratio - the length of the malleus arm is greater than the incus arm
- Buckling action - force is transmitted from the center of the tympanic membrane
What two properties determine an objects resonant frequency (determined by acoustic impedance)?
Mass - heavier objects vibrate at lower frequencies
Stiffness - less elastic objects vibrate at a higher frequency
What structures affect mass and stiffness of the middle ear?
Ossicles contribute mass
Volume of the middle ear space affects stiffness
What do you worry about with otitis media?
Speech development
Maximal loss of 40-55dB
Low freq sounds like speech are affected first
High freq sounds are not affected until the mass of middle ear bones is increases
How do diseases of the middle ear progress with hearing loss?
Low freq (stiffness/space) first
High freq (mass/ossicles) later
What is otosclerosis?
Abnormal growth of bone in the middle ear
Results in immobilization of the stapes
Can occur in the cochlea adding sensorineural loss
Common cause of bilateral gradual hearing loss I’m adults
70% hereditary
2x in females
More common in whites
Repaired surgically
Where is the Na rich perilymph?
In the bony labyrinth
Where is the K rich endolymph?
In the membranous labyrinth
What is contained in the membranous membrane?
Receptor hair cells in a gelatinous matrix
Where are the six receptive fields of the inner ear?
3 cristae ampullaris. 1 in each semicircular canal
2 maculae ( one in each the saccule and utricle)
1 organ of corti (cochlea)
What is the common histology of the 6 receptive areas?
I and II type receptors
Supporting (sustentacular) cells are the hair cells
Gelatinous matrix overlying the hair and supporting cells
Afferent and efferent innervation
What receptors do sensory fibers usually have?
Type I hair cells
What receptors do motor fibers usually have?
Type II hair cells
Where does CN VIII exit?
The cranial vault with CN VII through the internal auditory meatus
What for things does the Vestibularcochlear nerve split into when it is in the auditory meatus?
- Cochlear nerve to the organ of corti
- Superior division of the vestibular nerve to and from the utriclar macula, and the ant. and lat. ampullaris
- Inferior division of the vestibular nerve to and from the saccular macula
- Nerve to and from the posterior cristae ampullaris
What are the two types of hair cells?
Type 1 - true receptors
Type 2 - amplifiers
What is the shape of type 1 hair cells?
Pyriform in shape
Have a globular base containing the nucleus
What is the shape of type 2 hair cells?
Cylindrical with a centrally located nucleus
What is the arrangement of hair cells in the vestibular system?
Type 1 and 2 are randomly arranged within receptive regions
What is the arrangement of hair cells in the cochlea?
Precise
Type 1 are called inner hair cells
Type 2 are called outer hair cells
Based on their position within the organ of corti relative to the modiolus
What are the three aspects of hair cell structure that is critical to their function?
Both types are mechanoreceptors
Type 1 and 2 have diff afferent and efferent innervation
In the cochlea out hair cells (OHCs) have specialized lateral cisternae and other structural adaptations that support their function as contractile units
How many hair cells does 1 afferent nerve supply for type 1 receptors?
1 hair cell
How many hair cells does 1 afferent nerve supply for type 2 receptors?
Many
What type of receptor for hair cells do efferents have direct large contact with the OHC somas?
Type 2
What displacement is depolarizing for hair cell transduction?
Toward the tallest row of stereocilia also called positive deflection
In the cochlea this corresponds to movement towards the scala vestibuli
What displacement is hyperpolarizing for hair cell transduction?
Towards the shortest row of stereocilia
Corresponds to movement towards the scala tympani
What are the two components of the vestibular system?
Semicircular canals (motion detectors)
Otolith organs (utricle and saccule) (gravity detectors)
A lesion to what structure would cause the sensation of spinning?
The semicircular canals
A lesion to what area would induce the sensation of tilt?
The otolith organs (utricle and saccule)
Gravity detectors
What is responsible for fixating the visual image on the fovea?
The vestibular system
What output is integrated with the vestibular system and perceived as the same?
Proprioception = perception of body in space
However for others it is used as a reference postural system
What way of deflection does stereocilia cause depolarization in the semicircular canal?
Horizontal - toward the utricle
Anterior and posterior - away from the utricle
How does depolarization occur of the horizontal canals in relation to head movement?
The same direction as head movement
Left head turn depolarized the left horizontal canal
What is the natural pairing of anterior/posterior canals?
Left anterior with right posterior
Right anterior with left posterior
How are the anterior and posterior canals related to each other?
And 90 degrees
The anterior canal is 41 degrees to the sagital plane
What is the preferred angle for stimulation of the
A/P canals?
Opposite for the anterior canal on one side and the posterior canal on the other
What does tilting your head forward do to your a/p canals?
Depolarization of the anterior canals
Hyperpolarization for the posterior canals
Bottom line, for the A/P canals depolarization occurs in the same direction as head movement
What are the otolith organs?
The saccule and utricle
Detect gravity (linear acceleration)
What are otoconia?
Small calcium carbonate and protein particles embedded in the overlying gelatinous otolith membrane
They produce drag on the stereocilia when the head changes position
What is the orientation of the hair in the utricle and saccule when the body is in anatomical position?
The patch of hair cells in the utricle is nearly horizontal, stereocilia are vertical
In the saccule the hair cells are vertical and the stereocilia are horizontal
How is directionality conferred in the otolith organs?
Solely by the orientation of the hair cell stereocilia
This is opposed to the semicircular canals where the orientation of the canals confers directionality
What is the striola?
A curved dividing ridge that runs through each macula
What is the orientation of the kinocilia in the utricle and saccule?
Utricle - kinocilia toward the striola
Saccule - kinocilia away from the striola
In any position some hair cells will be depolarized and others hyper polarized in both otolith organs
What is characteristic of rightward nystagmus?
Slow movements to the left
Fast movements to the right
(Saccade gaze is fast)
(Pursuit gaze is slow)
What is pursuit controlled by?
The vestibulo-ocular reflex
What is saccade controlled by?
High centers like the cortex
What is positional alcohol nystagmus?
Nystagmus caused by alcohol
How does alcohol cause nystagmus?
Alcohol changes the relative density of the cupulae and the endolymph
Preferentially entering the cupulae making them less dense than the endolymph
When alcohol has entered the cupulae what is caused when the head is lying on its right side?
Right beating nystagmus
However when alcohol leaves the cupulae you get the opposite eye nystagmus
What is Benign paroxysmal positional vertigo (BPPV)?
Age or trauma can cause otoconia to detach from the utricle and log into the semicircular canal (usually posterior)
What is the most common cause of vertigo?
Benign paroxysmal positional vertigo
How is BPPV detected?
By the Dix-hallpike maneuver
What are some clinical signs of BPPV?
- Patient prefers to lay with the effected ear up
- Lag period of a few seconds
- Rolling spin
- Vertigo is triggered by movement in the opposite direction, nystagmus is reversed
- rapid onset for 20-30 sec
- disrupts nearly all life
- often self resolves
What maneuver can return otoconia to the utricle in BPPV?
The Epley maneuver
What is labyrinthitis?
Inflammation of the inner ear Usually viral 1-2 weeks after the flu May cause hearing loss or tinnitus No treatment for viral cases
What is required for hearing transduction to occur?
The basilar membrane to vibrate. Inducing stereocilia deflection in the hair cells
What is the directionality of hair cell transduction in hearing?
Toward the scala vestibuli is depolarizing
Toward the scala tympani is hyperpolarizing
How is sound transmitted from the basilar membrane?
Not due to the pressure wave but to the basilar membrane resonating after the pressure wave
Therefore establishment of the traveling wave vibration is independent of how motion is induced in the perilymph
What lymph is contained in the scala vestibuli, tympani, and media?
Scala vestibuli and tympani is perilymph
Scala media is endolymph
How does sounds pressure travel through the cochlea?
When sound is delivered to the oval window, it will a send from the base of the scala vestibuli to the apex where it is transferred via the helicotrema to the scala tympani the sound pressure will then travel back down to the round window where it will be relieved
What is the bony core of the cochlea?
The modiolus
Defines the medial direction in the cochlea
Surrounded by bony spiral lamina
What is around the modiolus?
The three scalar wrap around it on the spiral lamina
Three times
Where do the scala vestibuli and tympani join?
At the helicotrema
Where is the basilar membrane?
In between the scala tympani and media
It supports the organ of corti
Where does the auditory nerve run?
Through the modiolus
Apical fibers are found In the core of the nerve bundle and basal fibers toward the outside
This preserves the tonotopic relationship
What are the three main functional regions around the scala media?
Organ of Corti - sensory hair cells that transducer sound into a receptor potential
Spiral ganglion - cell bodies of the sensory neurons that send action potentials to the brain stem
Stria Vascularis - produces endolymph and generates the endocochlear potential
Where do nerve fibers to the inner ear become unmyelinated?
When they pass through the habenula perforata to reach the hair cells
What is the function of the stria Vascularis?
Adjacent to the spiral ligament, this is a critical part of K recycling, that moves K into the scala media.
Also generates the endocochlear potential
