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Hearing anatomy
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76
Anatomy
Undergraduate 4
11/27/2008

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Cards

Term
components of the peripheral system
Definition
Outer ear, Middle ear, inner ear (cochlea) and the AN
Term
Components of the Central System
Definition
CN, SOC, LL, IC, MGN, Auditory subcortex, and cortex, interhemispheric pathways
Term
Location of the peripheral system
Definition
Temporal bome
Term
Location of the Central system
Definition
Pons- CN, SOC, LL Midbrain-IC and thalamus-MGN
Term
primary Auditory cortex
Definition
Internal Capsule, insula, heschl's gyrus, Planum temporale, superior temporal gyrus
Term
Auditory Responsive areas
Definition
Frontal Lobe, Parietal, Angular gyrus, supramarginal gyrus, Corpus callosum
Term
Afferent Auditory system
Definition
Bottom-up processing; periferal to central, from the ear to the brain
Term
Efferent Auditory system
Definition
top-down processing; central to peripheral; from the brain to the ear
Term
Auditory Processes-1. Sequential Processing
Definition
Information is transferred from one area or level to the next; hieracharchal organization; involves entire auditory system
Term
Auditory Processes-1. Sequential Processing 2. Parallel Processing-
Definition
overlapping functions: at the same time, at different locations; occurs throughout the neural system
Term
Auditory Processes-1. Sequential Processing 2. Parallel Processing 3. Inhibition and excitation
Definition
balanced throughout all types of auditory processes
Term
Outer Ear
Definition
portal for sounds--> enter as acoustic nrg; pinna, external auditory meatus (ear canal)
Term
Middle ear
Definition
Convert sounds: from acoustic to mechanical nrg; air filled space with 3 ossicles- smallest bones in the human body; tendons from two muscles; branch of the facial nerve (CN 7); Impendence matching system
Term
Petrous portion of the temporal bone
Definition
deep; middle ear anc cochlea; IAM- houses AN and Facial nerve
Term
Parts of the temporal bone
Definition
squamous, tympanic, mastoid, petrous
Term
Inner ear
Definition
cochlea- modiolus, osseous, spiral lamina, membranous labryinth
Term
modiolus
Definition
peforated bony central core of the cochlea
Term
osseous spiral lamina
Definition
bony shelf spirals around modiolus from base to apex
Term
membranous labyrinth
Definition
scala vestibuli(upper), scala media, scala tympani (lower); basilar membrane (floor of the scala media); ressiner's membrane (floor of the scala vestibuli); helicotrema
Term
cochlear fluids
Definition
Perilymph- scala vestibuli, scala tympani, like CSF- High sodium; low potassium
Endolymph: High Potassium, low sodium, scala media; cortilymph: scala media
Term
ogan of corti
Definition
End organ of hearing, auditory sensory receptor cells;
-Converts mechanical nrg to electrical nrg
-rests on the BM
--> outer hair cells; inner hair cells
--> tectorial membrane; stereocilia
Term
Cochlear Mechanics 1. Travelling Wave
Definition
Compression: Pushes inward; basilar membrane moves downward; rarefraction: basilar membrane moves upward
Term
cochlear mechanince 1. Travelling Wave 2. frequency
Definition
Frequency: Location on the basilar membrane--> tonotopicity
-firing rate of the auditory neurons
Term
cochlear mechanince 1. Travelling Wave 2. frequency 3. Intensity
Definition
Amplitude of the traveliing wave envelope; magnitude of the basilar membrane displacement
Term
hair cell mechanics
Definition
convert mechanical nrg into electrochemical nrg
-outer hair cells expand and contract
-> shifts BM displacement
-> stereocilia sheared by the tectorial membrane
->Downward pressure results in hyperpolarization and inhibition
-> Upward pressure results in depolarization and excitation
Term

auditory nerve

Definition
  • part of the CN 8
  • contains about 30,000 fibers
  • fibers begin at hair cells--> run through the habenula perforata; openings in the osseous spiral lamina
  • go to rosenthals canal--> contains spiral ganglion cells
  • From the modiolus; trunk of nerve fibers
  • enter the internal auditory meatus
  • Type 1 fibers--> larger more mylenated, more numerous, connect to inner hair cells
  • Type II fibers--> cnnect to outer hair cells
Term
Frequency coding
Definition
  • phase-locking
  • fibers can respond only up to 1000 HZ
  • Volley principle- used in response to frequencies higher than 1000 Hz
  • each fibers responds less often
  • others fibers recruited to help respond
Term
Intensity coding
Definition

higher intensities

  • more auditory nerve fibers
  • greater firing rates
Term
cochlear nucleus
Definition
termination of all auditory nerve fibers; has 3 output routes (ventral stria, dorsal stria, intermediate stria); ventral stria imp't for sound detection in quiet and in noise; has similar tonotopic organization to cochlea and AN
Term
Superior Olivary Complex
Definition
tonotopic arrangement; first bilateral representation of auditory input; important for fusion, lateralization, and localization; interaural intensity; interaural timing; acoustic reflex
Term
lateral leminiscus
Definition
upper pons, has dorsal and ventral nuclei; inputs from the CN and SOC, contributes to localization and lateralization
Term
ABR
Definition

Auditory brainstem response; has 5 primary waves

Waves 1 and 2- AN

Wave 3- CN

Wave 4-SOC

Wave 5- LL

Term
Inferior colliculus
Definition
  • midbrain
  • tonotopic
  • phase-locking
          • amplitude-modulated signals
      • gap detection
Term
Medial geniculate
Definition

thalamus

has 3 main parts- ventral, medial, and doresal

major inputs form ipsi IC

Output to cortex--> venttral through internal capsule to A1

medial: through External capsule to insula

Dorsal: through internal capsule to secondary AC and insula

Term
Auditory Cortex
Definition
    • recieves input from the MGB
  • thalamo cortical pathway
  • thru the internal capsule)
    • gray matter- nucliei of nerve fibers; sulci(grooves or folds in cortex); gyri (bulges in neural tissue); sylvian fissure (hescl's gyrus; primary auditory area) planum temporale
    • tonotopic org
    • coding-intensity-more fibers, higher rates; excitatory and inhibitory changes; temporal coding-only up to 100hz
    • speech- greater left than rite hemisphere responses to speech
    • Late components of MLR; N1-P2 complex; mismatch negativity
Term
Corpus callosum
Definition
connects to brain's hemisphers; large mylenated axons; sulcus- contains most suditory neural finers; fibers from superior temp gyrus and insula; splenium- initially thought to be primarily visual system; lesions in splenium will affect auditory processing durin dichotic listening
Term
Efferent system
Definition
  • forms a feedback loop with the afferent system; rostral system-auditory cortex, MGB and iC; caudal system- Olivocochlear bundle and cochlea;
  • impt for inhibitory activation; hearing in Noise; prtection from noise
Term
Middle Ear Space
Definition
Hard-walled cavity in the temporal bone, filled with air, air pressure regualated by the Eustachain tube
Term
3 layers of the TM
Definition
  1. Outermost layer is continuous with the epidermal lining of the EAM- helps move debris, involved in spontaneous healing, innervated by cranial nerves V and X
  2. Intermdiate fibrous layer-provides support; radial and cirular fibers
  3. inner layer derived from membranous lining (mucosal) of middle ear cavity
Term
annulus
Definition
region of the TM; thick ring attached to the Temp bone
Term
Anterior and posterior malleolar folds
Definition
ligament bands at the upper region of the TM
Term
Pars flaccida
Definition

small region above the malleolar folds

sparse fibers 

Term
pars tensa
Definition
majority of the surface of the TM; dense fibers, taut
Term
Umbo
Definition
Point of attachment to manubrium of malleus
Term
tensor tympani muscle
Definition
  1. attaches between anterior wall and neck of the malleus
  2. increases tension on the TM by pulling the manubrium inward
  3. pulls mallueus in anterior and posterior directions
  4. Innervated by the 5th CN
Term
stapedius muscle
Definition
  • head of the stapes
  • pulls stapes rearward to fix footplate in the oval window
  • innnervated by the 7th CN
Term
Eustachian Tube
Definition
  1. Connects middle ear space with the lateral wall of the nasopharynx
  2. allows air to pass from the nasopharynx to the middle ear space to equalize pressure on both sides of TM
  3. Muscles innnervated by the 11 cranial nerve (the spinal accessory nerve
Term
Impedence
Definition

Opposition to the flow of energy

Mass reacts directly with frequency

Stiffness refers inversely with frequency 

Term
Tympanometry
Definition
  • measures changes in stiffness of the TM
  • 226 Hz probe tone at 80 dB SPL
  • Air pressure varied in the EAM
  • TM
    • stiffens with positive and negative air pressure
    • is most compliant when at normal position
Term
Sound Transmission
Definition
  • Catenary Principle (helmholz)-Greater force at the center of the TM than at the edges
  • Isoamplitude regions of TM
    • Maximum displacement is frequency dependent
  • Ossicular chain not uniform across intensities
    • rotation around vertical axis at posterior region for moderate sounds
    • rotation around horizontal axis at high intensities
    • more tilting or rockin, less pisto-like at higher levels

 

Term

Middle Ear Transformer

AREA 

Definition

DECRESES FROM tm TO OVAL WINDOW

PRODUCES A 17 FOLD INCREASE IN PRESSURE 

Term

Middle Ear transformer

VELOCITY 

Definition

(buckling effect)

malleus manubrium moves less than the TM

Produces a two-fold increase in pressure 

Term

Middle Ear Transformer

LEVER ACTION

 

Definition

Decreasing Length of the ossicles

produces a 1.3 fold increase in pressure  

Term
Middle Ear transformer
Definition

Overall effect

17:2:1.3=44.2 

Term
Bone conduction
Definition

Sounds can vibrate bones of skull directly

Inertial vibrational forces: condensation and rarefaction; predominant for low frequency sounds

Compressional hearing: at higher frequencies of sounds; segmental differences in vibrational patterns 

Term
Traveling Wave
Definition
  • George Von Bekesy and The Mossbauer technique
  • Cochlear fluids are non-compressible
  • Pressure waves travel from base-apex and back again- fluids displaced along the entire length of travel, causes transverse pressures and vertical displacements along the basilar membrane, fluid bulge, compression waves drive BM downward; rarefaction waves drive it upward

 

Term
Mossbauer Technique
Definition

Detected gamma rays from radioactive probe

could measure the velocity of the malleus and the BM

Frequency tuning curves: peak occurs at the place that matches frequency of stimulus

sharper tuning curves than von Beckesys

Term
Travelling Wave Velocity
Definition

Decreases: -100 m/sec at the base

-2 sec at the apex

Amplitude of wave increases- is about 10 times greater at apex 

Term
Place Theory of Hearing
Definition
  • Helmholz, 1863
  • BM changes physical properties from base to apex
    • structure resonates to diff frequencies at different places along length
    • tuned like strings of a harp or piano
    • sounds induce sympathetic vibration at places along the BM, depending upon freq
Term
Frequency Analysis
Definition
  • changes in frequency shift the place of maximum displacement
  • distributes the nrg to hair cells along the length of the cochlea

 

Term
Nonlinearity of the Cochlea
Definition
  • Higher intensity-frequency response is broader
  • Displacement is greater
  • involves compression
Term
cochlear amplifier
Definition
  • low level signals get this boost in BM displacement
  • helps the inner hair cell detect the presence of the signal
  • this repersents the active component of the BM displacemnt
  • will be swamped by the passive component at high signal levels
Term
nonlinear tuning curves
Definition
  • Fairly sharp toward lower frequencies
  • Extremely sharp toward higher frequencies
  • sharpness increased at lower intensities
Term
Negative damping
Definition
  • a different term for amplification
  • an increase in response from the BM to softer levels of stimulus
Term
Evidence of Negative Damping
Definition

Laser velocimetry studies measured 2 things, velocity of the BM as a fxn of freq and intesity;gain-magnitude of displacement, normalized to stimulus pressure

Term
Gain measurements
Definition
  1. Largest gain seen for the softest stimulus level of 0 dB SPL
  2. Gain is approx 50 dB
  3. Means that the BM is boosting the input signal at low signal levels
  4. Amt of gain decreases as signal instensity increases 
Term
Compression Wave
Definition
  1. Stapes Moves inward
  2. Perilymph in the scala vestibuli is compresseds
  3. Deflects the scala media downward
  4. organ of corti remains relatively uniform
  5. triangular shape of pilar cells keeps shape of the tunnel of corti intact
  6. hair cells in the stereocilia are deflected
Term
Motility of the outer hair cells
Definition

OHCs contract when BM moves upward

OHCs expand when BM moves downward

 

Term
Tip links
Definition

Open pores to allow ion flow in

when cilia are deflected towards the tallest cilia

away from limbus

excitatory mode

essential for transduction

drives in potassium and calcium ions 

Term
Stria vascularis
Definition
  1. maintains the ionic composition of the endolymph
  2. inside hair potential is -40to -70
    1. voltage drop across apex of hair cells
    2. opening and closing of mechanically gated ion channels- produces variable resistance; drives K+ into the cells
Term
Excitation
Definition
  • deflection of stereocilia away from limbus
  • increases the number of open transduction channels
  • inward flow of K+
  • depolarization of hair cell 
Term
inhibition
Definition
  • deflection of stereocilia towards limbus
  • decreases the number of open transduction channels
  • less inward flow of K+
  • Hyperpolarization of hair cell
  • inhibition
Term
Transduction
Definition
conversion- from mechanical vibrations to electrical activity
Term
Mechanically gated transduction channels
Definition
located at the tips of stereocilia; pulled open by tension applied to the tip-links' transduction occurs through these channels
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