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)