Anatomy and Physiology of Hearing Mechanisms
Resting Potential for IHC
-44 mb
Resting Potential for OHC
-70 mb
Cochlear Nucleus sturctures
3 parts: anteroventral cochlear nucleus, Posteroventral cochlear nucleus, Dorsal cochlear nucleus
Afferent Type II (outer spiral)
5% of afferent fibers innervate OHC
What is the upper frequency where timing codes are effective
5000 Hz
Afferent Type I (radial)
95% innervate the IHC only. tend to be thicker. 1 to 1 coverage= 1 afferent fiber per hair cell
Pars Tensa
A fibrous tissue layer between the skin lining the external ear canal and the mucous lining of the middle ear
Cochlear microphonic
Alternating current that only occurs during the presentation of an acoustic stimulus. appears to mirror the waveform of the acoustic stimulus (mostly from OHC)
Umbo
Central location on the tympanic membrane where the tip of the manubrium of the malleus is attached
Structure of Inner Ear
Cochlea, semicircular canals,
Eustachian Tube
Connects the middle ear to the nasopharynx. Opened during chewing and swallowing to equalize air pressure.
Function of the Middle Ear
Convert acoustic energy into mechanical energy by using lever action. Increase pressure in order to displace the fluids of the inner ear
Manubrium
Handle (or long process) of the malleus that is attached to the tympanic membrane.
Tympanic Membrane
Made of cross hatch fibers (pars tensa). Separates the ear canal form the middle ear. Converts acoustic vibrations entering the ear into mechanical vibrations of the middle ear ossicles.
Name the Ossicles
Malleus, Incus, Stapes
Parts of the Malleus
Manubrium, Neck, Lateral Process, Anterior process, head
4 Cochlea potentials
Resting Potential, Summating Potential, cochlear Microphonic, Action Potential
Resting potential
Scala tympani= 0 mV Scala Vestibuli= +2-5 mV Scala media= +80-100 mV, endocochlear or endolymph potential
Spontaneous OAE (otoacoustic emission)
Single pure tones generated with cochlea. measured without stimuli
Botcher cells
Small, short square cells, for support
Middle Ear Muscles
Tensor tympani, Stapedius
Structures of the Middle ear
Tympanic membrane, Ossicles, Eustachian Tube
Parts of the Temporal bone
Tympanic, mastoid, squamous, and petrous
Phase-locking
a characteristic pattern of neural discharges in which theyh always fire during the same phase of the stimulus, usually for CFs below 4000-5000 Hz
Summating Potential
a stimulus related Direct Current electrical responses recorded from the hair cells. represents stimulus envelope= duration and not waveform= frequency
Modalis
air filled space in the center of the cochlea
Primary or first order fibers
auditory nerve fibers that exit the cochlea and synapse in the cochlear nucleus
Second order fibers
auditory nerve fibers that exit the cochlear nucleus and synapse at ta higher structure
Stria Vascularis
balances the nutrients and the ionic charge within the scala media, (potassium)
Parts of the Incus
body, short process, long process, lenticular process
Efferent Fibers
bring information from higher neural centers to the auditory periphery. (touching either hair cell or afferent fibers)
Direction of balance for the Inferior canal
cartwheel
Structures of the inner ear
cochlea, vestibular canals, vestibule
Boarder cells
completely surround the IHC
Reticular lamen
connects across, sits on the heads of the different hair cells
When IHC gets to -20
depolirization
Dieter Cells
directly inferior to the OHC
Lateral Lemniscus
divided into 3 regions, receive, transmits and processes information from the CN and SOC
After onset of the PST, what does the discharge rate do
drops to nearly zero or below the spontaneous rate, then resumes
Lateral Superior Olive efferent fibers
efferent fibers from here project predominantly to the IHC
Medial Superior Olive efferent fibers
efferent fibers from here project to the OHC and these fibers synaps directly on the OHC
Bony labyrinth located
embedded within the petrous portion of the temporal lobe
Transient Evoked
evoked by click stimuli. 1500 hz-5000hz, on the basilar membrane
Distortion Product
evoked by two pure-tone frequencies. (want the ohc to be higher than the background noise)
Kinocilium
farthest, (tallest) and thinker hair cell, in charge of creating displacement of potassium
Superior Olivary Complex
first anatomic location for biaural input, this is crucial for sound localization in space
Scala of media fluid
fluid turns into endolymph
Scala of Vestibule and tempany fluid
fluids of perilymph
Divergent Fibers
found in type II afferent splits and inervate with multiple OHC, help contribute to the displacement to create depolarization in IHC
Tonotopic orginazation
frequency displacemtn
Parts of the Stapes
head, anterior and posterior crura, footplate
Auditory nerve fibers discharge rate
increase over a range of 20-50dB
Rate level functions
increase the level of the acoustic stimulus and measure the change in discharge of a single neuron about the spontaneous rate
What is the function of the efferent system
inhibitory to the afferent
Tensor Tympani
inserts into the manubrium of malleus
Stapedius
inserts into the posterior portion of the neck of the stapes
Auditory Cortex
located in Heschl's Gyrus. projections to the cortex contain bilateral information. organized in columns allowing to organize complex pattern recognition
Nedial Geniculate Body
located in the thalamus, receives binaural input from inferior structures
Hence cells
longer, lateral, supports OHC
Which frequencies can bend easier
low frequencies
Ampulla
membranous portion of semicircular canals, connects to the uricle with an enlarged sac
Type I hair cells
more critical to the vetibular processing, surrounded by afferent nerve fibers.
Otoconia
more dense than endolymph and hair cells are displaced by inert , not endolymph movement. move on their own
Condensation Click
move the oval window inward so the basilar membrane moves downward causing a delay in excitation of the hair cells
Rarefraction Click
move the oval window outward so the basilar membrane moves upward causing excitation of the hair cells and nerve fibers fire earlier
high frequencies
near the basal end, sharp roll off
Pinna
outer ear, made of cartilage. Collects auditory stimuli and funnels it into the ear canal
Nerve Bundle organization
outside ring are high frequencies, middle, then low frequencies
Response area
plots each frequency the nerve fiber responds to for a fixed stimulus level
Otoacoustic emmission
preneural potentials that are acoustic signals detected in the ear canal. (evaluating OHC contractions)
Extreme Vastularous
pumps in endolymph
Inferior colliculus
receives inputs from both the SOC and CN, neurons in the IC respond to monaural input where other neurons respond to binaural
Function of the cochlear nucleus
refine the acoustic signal form the cochlea, fibers exiting the CN innervate most of the other nuclei in the brainstem
Medial Superior Olive
responds to interaural timing cues and have low frequency CF
Bony Labyrinth structures
semicircular canals, vestiblule, cochlea
Membranous Labyrinth structures
semicircular ducts, uricle, saccule
Afferent Fibers
sensory fibers that carrry information from the organ of Corti to the brainstem and brain. (always touching hair cell)
Risner Membrane
separates scala media and vestibula
Tectorial membrane
slug like thing directly superior to hair cells
When stereocili are deflected towards the tallest
small ion channels at top are opened, Exciting
Typpe II hair cells
small symnaptic connection
Lateral Superior Olive
sound localization based on level and time differences, neurons have high frequency CFs due to degree of diffraction
Steriocollia
spike like things, tiny hairs that are protected in the cuticular plate at the tip of each OHC and IHC
Basal membrane
structure that holds organ of corti
Direction of balance for the Superior canal
summer saults (tumbling)
Direction of balance for the Horizontal canal
tea cups
Low frequencies
the apical end, more gradual rise and fall
Tuning Curve CF
the frequency of the neurons lowest threshold
Characteristic Frequency
the frequency where the basilar membrane or auditory nerve fiber is most sensitive;
Post Stimulus Time
the greatest number of discharges occurs at the onset, discharges decreases quickly.
Single neuron threshold
the minimum stimulus level that will cause an increase in the discharge rate above the spontaneous activity
Discharge rate
the number of times a fiber discharges or fires in a given time period
Action Potential
the sum of potentials of many individual nerve fibers firing together. reflects the neural output of the cochlea specifically the action potential is asssociated w/ wave 1 of the auditory brain response
Neuroepithelium
the supporting cells for hair cells
Where is tonotopic organization maintained
throughout the nuclei of the CAS
Function of the cochlea
translate the mechanical vibrations of the stapes and the inner ear fluids into neural responses in the auditory banch
Tunnel of corti
triangular tunnel
Otolith organs
uricle and saccule
In intense noise situations what does the efferent system do
uses the inhibitory effects to dampen noise protecting the neural system
Cerumen
waxy substance produced by glands in the external auditory canal that helps protect lubricate and clean the canal. (ear wax)
Neuronal Dynamic Range
where dischare rate changes or starts to plateu
Habenula Perforata
where the afferent and efferent fibers enter or exit the modalis
Helicotrema
where the two scalas meet (apex)