Audiology Anatomy and Physiology

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The anulas of the TM has an opening or diffiency on top called?: The notch of Rivinus
Parts of the Tympanic Membrane: -Pars flaccida aka Schrapnell's membrane
-long process of the incus
-manubrium of the malleus
-umbo
-pars tensa
-annular ligament
-cone of light
-chorda tympani (branch of facial nerve)
-Notch of Rivinus
The tympanic membrane increases force at the central point according to what principle?: Catenary principle of Helmholtz
Concha resonance frequency of a male is about: 4500 Hz
Arteries that supply outer ear?: -external carotid artery
-superficial temporal artery
-posterior auricular artery
What is the pyramidal eminance?: A bulge in the posterior wall of the ME cavity that houses the stapedius muscle

the stapedius enters here & attaches to head of stapes
Contents of Middle ear cavity, ossicular chain: -malleus,Incus,Stapes
-lateral ligament of malleus
-superior ligament of malleus
-posterior ligament of the incus
-stapedius muscle
-annular ligament of stapes
-anterior ligament of the malleus
-tensor tympany
Name the two muscles in the ME space? Inervated by?: Tensor tympani -inervated by the V nerve or trigeminal

Stapedius - inervated by VII (facial nerve) and several ligaments
the Eustachian tube opens upon action of the ?: Levator veli palatini & tensor veli palatini
The enclosed air in the middle ear cavity is what in nature... and provides what?: is stiff in nature
-provides tuning of ear, the volume of air acts as a filter that limits low frequency sounds
-the outer ear emphasizes and de emphasizes high frequency sounds (tuning)
The middle ear cavity boundaries are?: -Lateral = TM in squamous portion of temporal bone
-Medial wall = promontory, round window, oval window, prominance of facial nerve,tympanic nerve
-Anterior wall = Eustachian tube perf, orifice of tensor tymp tendon, carotid canal
-Posterior wall - mastoid wall, tympanic aditus, fossa incudis, pyramidal eminance, aperature for VII nerve
-Inferior wall= Tympanic plate, juggular fossa
-superior boundary = Tegman tympani
If the Stria vascularis is damaged what happens to the endocochlear potential?: It will no longer be present and the inner ear no longer performs its function of transferring mechanical energy into electrical energy
The spiral ligament: situated between the otic capsule wall & the stria vascularis
-it covers the entire lateral wall of the scala media & extends inferiorly into upper part of scala tympani
-provides support to Basilar membrane & reisners membranes anchoring the lateral aspect of the BM
-may aid in ionic balance of cochlea
The Stria Vascularis: -highly vascularized
-it is believed that the chemical relationship between perilymph & endolynph is maintained by an active process in the stria vascularis.
-Endolymph is likely produced in complex manner but the stria is the main player
-located in the scala media outer edge,inside the spiral ligament
The Tectorial Membrane: A gelatinous flap composed of collagen & proteins
-attached to the spiral limbus on one side and Hensen's cells on the other
-sits immediately above organ of Corti and covers the entire length of it.
-plays important role in articulating with the stereocilia of OHCs
-the underside has notches to accomodate the tallest outer hair cells.
-no contact with IHCs
Various parts of the Organ of Corti: Type 1 neurons
type 2 neurons
OHCs, IHCs
Deiter, Boetcher, Claudian,sulcus,Hensens cells
Pillar cells
Tunnel of Corti
Space of Nuel
reticular lamina
efferent nerve fibers
tunnel radial fibers
habenula perforate
auditory nerve
perilymph (scala tymp&vestibuli)
endolymph (scala media)
Corti lymph in tunnel of corti
2 fluid pathways or aqueducts in the inner ear?: 1.The vestibular aqueduct/endolymphatic duct
- opens to IAM
-regulates endolymphatic pressure
-over or under absorption of endolymph
-implicated in endolymphatic hydrops
2.Cochlear Aqueduct (perilymphatic)
-contains perilymph
-goes from scala tympany to subaracnoid space
-allows for transfer of CSF become closed by about 50 yrs old
Several compartments of the body contribut to the pressure of the perilymph they are?: -Cranium (via cerbrospinal fluid)
-Middle ear space (via oval &round windows)
-Blood pressure (via the inner ear vasculature)
The ganglion cells of the AN converge in an enlarged area called?: Rosenthal's Canal
Cilia are composed of?: Actin filamants
Approximately 20 type I spiral ganglion neurons make a 1:1 contact with the base of each: Inner hair cell
The spiral ligament is the lateral point of attachment for the ?: Basilar membrane
The Vestibular aquaduct or does what?: It is a channel containing endolymph, it communicates with the endolymphatic sac and duct
function of Deiter's cells: Support OHCs
-each Deiter cell may contact as many as 5 OHCs
Function of Hensen's cells: Lateral to Deiter's cells
-help support the outer tunnel of corti
Nerve fibers of the cochlea: -attach to bottoms of hair cells & travel through the habenula perforata
-The cell bodies of these nerve fibers are in the modiolus, called spiral ganglion
Components of the membranous cochlea: Basilar Membrane
Reissners membrane
helicotrema
scalas tympani, vestibuli and media
Organ of Corti
Description of the cochlea: Embedded in the petrous portion of the temporal bone
-1cm wide and about 5mm from base to apex
-between 2.2 to 2.9 turns
-smaller at apex than at base
Point of attachment of neural fibers to hair cells in cochlea?: Terminal buttons
-thought to be a weak link as they are very fragile
What creates the pivot point of the stereocilia?: Cilia maintain a constant thickness along most of their length but taper to a narrow shaft as they enter the cuticular plate. This creates a point where they can pivot when they are deflected
Stiff objects are preferential to what frequency: high frequency
- they offer greater resistance to low frequency sounds
Massive objects tend to be preferential to what frequencies?: Low Frequencies
-they are greater resistance to high frequencies
What is the head shadow effect?: sound heard on the right side of the head will be received differently by the left ear because of the influence of the head.
-the level of the signal reaching the left ear is lower or softer
-not equal over frequencies
-low frequencies pass more easily around head and have negligible shadow effect
What is the Interaural intensity difference?: The difference between the intensity levels of the signal reaching the 2 ears
Mechanism of sound localization: Sound from the left side, activity in the left CN sent to SOC.
-Sound reaches right ear, activity in right CN
-impluses reach SOC at same time get summation -->action potential
what is characteristic frequency?: If an AN fiber was stimulated by a variety of tones of various frequencies, the freq that yielded the lowest threshold would be the characteristic freq
The nerve fibers of the inner ear can respond to many tones (besides their characteristic freq( but they must be presented at higher ______ in order to respond: intensities
If the intensity level for a threshold response is plotted for different frequencies, a ___ ____ is the result: tuning curve
The summating potential is a: DC response that follows the envelope of the signal
The cochlear microphonic is: An AC response that mimics the waveform of the tonal signal
The compound Action potential consists of 2 ___ ____s: negative deflections N1& n2 that occur at the onset of a signal
The auditory pathway has more synapses at nuclei than the ___ pathway: visual
Adaptation is?: the decrease in amplitude of AN action potential over time during consistent stimulation
-the longer the stimulus the greater adaptation
-adaptation greater for higher frequencies
-greater for individuals with moderate SNHL than normal or mild SNHL
-Tone decay acoustic reflex decay test will access this physiological response
-abnormal adaptation > 30dB of tone decay over 60 seconds sign of retrocochlear involvement
areas of interruptions in a neuron are called?: nodes of Ranvier
What are electric potentials?: They are differences in electrical charge between 2 points within the body-where there is a difference in electric charge between 2 points there is a potential for electric current flow
DC potential of the scala media? at rest the interior of a hair cell has potential of ?: scala media = 80 +mv high k+

-45 to -70 inside HC

-IHC's -40 to -50mv
-OHCs -70mv
Resting potential or endocochlear potential (CAP): -large DC electrical potential that can be recorded in the endolymph of the scala media
-thought to be generated by the stria vascularis
-due to high K+ in endolymph
-Always present whether or not stimulus is present
-the potential is +80 to +100 which makes it the largest resting potential in the body
The summating potential: -a DC electrical component
-there is a baseline shift in the summating potential only when there is an auditory stimulus
-thought to be a receptor potential of the hair cells. A receptor potential is the electrical response from a receptor cell that results when the cell is stimulated
- the strength of the summating potential is directly related to the intensity of the stimulus
Cochlear Microphonic: -An AC potential
-mirror image of incoming sound
-The CM accurately reflects the incoming sound stimulus
-The magnitude of the CM will be directly proportional to the magnitude of the BM movement
-if intensity increases the CM will increase
-thought to be generated by the cilia of OHCs predominatly
The mass & stiffness gradient along the length of the BM contributes to?: The overall tonotopic organization of the cochlea
Tuning curves at high frequencies look like what? Tuning curves at low frequ look like what?: Narrow & sharp w/higher Q10

Broad and not sharp lower Q10
Frequency tuning curves show what?: Plots of response thresholds as a function of frequency

- the closer the freq gets to characteristic frequency the less intensity it takes for us to hear so lowest thresholds
Action potentials are an ___ or ___ response: all or nothing
The human ear is most sensitive to what kinds of frequencies ?: Mid to high frequencies
How do you get the Q10 value of a tuning curve?: - measure the bandwidth at 10dB from peak, and divide into its center frequency

So if BW = 150
peak or center freq is 1000Hz
Q10 = 1000 divided by 150 = 6.67
- the bigger the BW the lower the Q10 and the broader the curve
The sharpness of an ANs tuning curve is dependent on ?: The health of the OHCs.
-damage to OHCs raises the threshold of the TC and rounds the tip
The max intensity range of the human ear is ?: - 110-120dB
Length of AN: 22-26mm
Length of BM: 25-35mm
Apical width = 450micometers
basal width = 150
How many efferent fibers in Inner ear?: 18,000
key neurotransmitters of the AN are: glutamate and Aspartate
Function of afferent fibers: -carry information from organ of corti to cochlear nucleus
-cell bodies are the spiral ganglion and axons are the 8th cranial nerve
-there are 30,000 afferent fibers
-85-95% of them innervate IHCs
3 types of neurons in the body are?: 1.Receptor neurons-receive stim from sensory receptor cells and in turn excite other cells
2. interneurons - receive information from one neuron and pass it along to the next
3. Motor neurons - recieve information from one neuron and in turn stimulate a muscle
When an acoustic stimulus is presented, it evokes a change in ?: the electrical current flowing through hair cells
The shortest route to the cortex is?: CN to IC to MGB to cortex
The auditory nerve starts at the____ of the cochlea and is the end of ____ _____: base

peripheral hearing
The internal auditory meatus houses?: the facial nerve (VII)
The auditory nerve (VIII)
the vestibular nerve (VIII)

The IAM is the site of most acoustic neuromas or vestibular schwanommas
Areas of the cortex that respond to sound?: Primary Aud cortex- Heschl's gyrus
planum temporal-posterior to Heschls
-left side site of Wernicke's area
-Supra marginal gyrus
-Angular gyrus
-Insula
-Claustrum
The primary aud cortex is located in ?: Brodmann's Areas and Wernick's area
(or Planum temporal)
Cortical neurons appear to be especially sensitive to ?: Changes in stimulation or modulations
The acoustic reflex is clinical tool for evaluating what?: Middle ear
cochlea
CN
SOC
Facial nerve
Functions of the Acoustic reflex: -Inner ear protection
-ongoing adjustments to input to inner ear so input is constant
-smoothing out mid ear transfer function
-improve hearing in presence of low frequency competing sounds
Clinical use of Acoust reflex testing: to assist in Identifying pathologies such as:
-ME effusion
-TM perfs
-tympanosclerosis
-eustachian tube dysfunction
-otosclerosis
-ossicular discontinuity
-Acoustic neuroma
-Cholesteatoma
Explain the mechanism of a maximum conductive HL: Will be 60dB
-comes from ossicular dysarticulaton
-30dB lost from lack of impedance matching
-15dB from lack of oval isolation
-15dB from TM blocking sound
4 parts of temporal bone?: Squamous - superior to ear canal
Mastoid - posterior to pinna
Petrous - houses inner ear and ear canal
tympanic - ear canal anterior and inferior
The external auditory canal: -lateral portion cartilage hair and cerumin in this part
-medial portion - osseous lined with epidermal skin
- enhances sound ~ 2700 Hz
The auricle functions effectively as a sound collector for frequencies around?: 5000 Hz
The tympanic membrane has how many layers?: 4 layers
What nerves innervate the EAM: Trigeminal
Facial
Glossopharyngeal
vagus
The tympanic membrane is composed of how many layers?: is composed of three layers:an outer cuticular layer,intermediate fibrous layer,and inner mucous layer.

the cuticular layer is continued with the skin of external acoustic meaus;

the fibrous layer lies b/w cuticular and mucous layer;

the mucous layer is continued with the mucous membrane of tympanic membrane.

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Created By josyg