Aud 700 Hearing Science Exam 2

Front 1

Outer ear structures

Back 1

Pinna- primarily made of cartilage
Concha- deep center portion
External auditory meatus- opening to the external auditory canal
External auditory canal- approximately 2-3 cm in length. First 1/3 cartilaginous with glands and hair follicles. Final 2/3 bony.

Front 2

Outer ear function

Back 2

Pinna collects auditory stimuli and funnels it into the ear canal.
Sound localization using two ears. Based on interaural time and level differences.
Wax, hair and orientation of canal protects TM.

Front 3

Tympanic membrane

Back 3

Most lateral portion of the middle ear. Cone shaped, pearl-white color.
Three landmarks:
1) Pars flaccida- most vulnerable portion for damage.
2) Pars tensa
3) Umbo- point of greatest retraction.

Front 4

Middle ear ossicles

Back 4

Malleus- manubrium of the malleus is embedded in the TM.
Incus- short process and a long (inferior) process.
Stapes- smallest bone in the body. Footplate of the stapes in the most medial portion of the middle ear.

Front 5

Middle ear muscles

Back 5

Tensor tympani- inserts into the manubrium of the malleus. Stiffens manubrium --> stiffened TM.
Stapedius- inserts into the posterior portion of the neck of the stapes. Smallest muscle in the body.
These muscles are the acoustic reflex.

Front 6

Eustachian Tube

Back 6

Most inferior portion of the middle ear cavity. Equalizes the pressure between the middle ear cavity and the external auditory canal.

Front 7

Function of the middle ear

Back 7

1) Converts acoustic energy into mechanical energy by using the lever action of the ossicular chain.
2) The TM and the ossicular chain increase pressure in order to displace the fluids of the inner ear (because of the higher impedance of the inner ear fluid). Area ratio and lever action work together to overcome impedance mismatch.
3) Limit distortions during transmission through the ossicular chain.

Front 8

Middle ear impedance

Back 8

1) Resistance- cochlear fluid on the footplate of the stapes.
2) Mass reactance- a result of the mass of the middle ear structures.
3) Compliant reactance- spring-like characteristics of the ligaments and muscles in the middle ear.

Front 9

Utricle

Back 9

Larger of the two sacs in the vestibular labyrinth.

Front 10

Vestibule

Back 10

Also an end organ of equilibrium but gives access to the cochlea.

Front 11

Cochlea

Back 11

Small, snail-shaped organ encased in the temporal bone. Base, apex and modiolus. Coils approximately 2.5 times and is about 35 mm in length, 1 cm wide, and 5 mm high.

Front 12

Scala vestibuli

Back 12

Region of the cochlea that connects the inner ear to the middle ear via the oval window/ stapes footplate. Contains perilymph.

Front 13

Scala tympani

Back 13

Lower region of the cochlea that terminates at the round window. Contains perilymph.

Front 14

Scala media

Back 14

Aka cochlear duct. Portion of the cochlea between the scala vestibuli and scala tympani. Bounded by Reissner's membrane, the basilar membrane, and the stria vascularis. Contains endolymph. Endolymph has a resting potential of +80-100 mV.

Front 15

Stria vascularis

Back 15

Produces endolymph and supplies oxygen and other nutrients (predominately blood) to the cochlea. Very important for survival of the structure.

Front 16

Basilar membrane

Back 16

Supports the organ of Corti which is the end organ of hearing. Inferior support for the organ of Corti.

Front 17

Tectoral membrane

Back 17

Superior support for the organ of Corti.

Front 18

Tunnel or Corti

Back 18

Triangular space between the OHCs and IHCs

Front 19

Stereocilla

Back 19

Tiny hairs that are rooted in the cuticular plate at the tip of each OHC and IHC. The tips of the tallest stereocilia are in contact with the tectorial membrane.
For OHCs, there are approximately 150 stereocillia arranged in three or more rows on each OHC in the shape of a V or W.
For IHCs, there are approximately 40 stereocilla arranged in two or more parallel rows that form a shallow U.

Front 20

Function of the cochlea

Back 20

To translate the mechanical vibrations of the stapes and the inner ear fluids into neural responses in the auditory branch of the 8th cranial nerve. Also to convert complex stimuli (multifrequency, such as speech) into individual frequency components.

Front 21

Depolarization

Back 21

The vibration of the fluid causes the basilar membrane to be displaced up, which causes the stereocilia of the hair cells to bend. The bending of the stereocillia causes the nerve at the base of the hair cell to initiate a neural potential which is sent along the auditory nerve.

Front 22

Single hair cell depolarization

Back 22

When the stereocilia are deflected small ion channels at the tip of the hair cell are opened.
Potassium (K+) ions enter the hair cell depolarizing the cell. Enters at base and tiplinks.
Depolarization (when IHC has about -20 mV) leads to a release of a transmitter (Glutamate and Aspertate) at the base of the hair cells.

Front 23

Resting potentials for IHC and OHC

Back 23

IHC about -45 mV
OHC about -70 mV

Front 24

Place theory

Back 24

Each point along the basilar membrane that is set in motion vibrates at the same frequency as the stimulus. The amplitude of the membrane vibration, however, is different at different locations, depending on the frequency and level of the input stimulus.

Front 25

Traveling wave

Back 25

The basilar membrane becomes wider as it gets to the helicotrema. Because of the variation in stiffness, different frequencies will cause maximum vibration amplitude at different points along the basilar membrane.

Front 26

Tonotopic organization

Back 26

For low frequencies, the maximum displacement of the basilar membrane is near the apical end. For high frequencies, the maximum displacement is near the basal end.

Front 27

Low frequencies displacement

Back 27

Low frequencies stimulate not only the apical end where the point of maximum displacement occurs but also at the basal end. The amount of displacement past the maximum displacement is reduced gradually.

Front 28

High frequencies displacement

Back 28

Higher frequencies stimulate only the basal end of the cochlea. The amount of displacement past the point of maximum displacement is reduced more rapidly.

Front 29

Basilar membrane

Back 29

For a given frequency, the basilar membrane acts as a low-pass filter with a sharp high-frequency roll-off. Furthermore, the basilar membrane also acts as a high-pass filter with a more gradual low-frequency roll-off. As a result, the specific frequency on the basilar membrane resembles a band pass filter of vibrating motion.

Front 30

Vestibular function

Back 30

Motion detection and sense of position in space. Vestibular, visual, and somatosensory information put together to produce fine control of visual gaze, posture, autonomotic reflexes, and spacial orientation.

Front 31

Vestibular dysfunction

Back 31

Dizziness, vertigo, and motion sickness are associated with dysfunction of the vestibular system. Most likely see an audiologist first for the above problems. Mineers: leak in the vestibular system.

Front 32

Types of motion

Back 32

Rotational (angular acceleration) - head turns.
Linear (linear acceleration) - walking, falls, vehicle travel, elevators, and head tilts from gravity.

Front 33

Bony labryinth

Back 33

Embedded within the petrous portion of the temporal bone and protects the sensory structures.

Front 34

Membranous labyrinth

Back 34

Contains 5 sensory structures.
Three semicircular canals: horizontal, anterior, and posterior.
Two otolith organs: utricle and saccule.

Front 35

Peripheral Vestibular Labyrinth

Back 35

Horizontal semicircular canal and utricle - lie in a 30 degree horizontal plane.
Anterior and posterior semicircular canals and saccule - lie in a vertical plane.
Structures on ipsilateral side work in opposition of structures on the contralateral side.

Front 36

Vestibular labyrinth fluid

Back 36

Perilymph - fluid surrounding the membranous labyrinth. High in sodium (Na+) and low in potassium (K+).
Endolymph - fluid within the membranous labyrinth. 7-10 mV resting potential. High in potassium (K+) and low in sodium (Na+). From cerebral spinal fluid.

Front 37

Ampulla

Back 37

Membranous portion of the semicircular ducts connect to the utricle with an enlarged sac called the ampulla.
50-100 stereocilia and a single, longer kinocilium. Type I - surrounded by afferent nerve fiber. Type II - single synaptic connection at the base of the hair cell. Afferent nerve fibers are the vestibular portion of the vestibulocochlear nerve (VII cranial nerve). Hair cells are embedded in supporting cells of neuroepithelium - crista. Fluid-tight (endolymph) structure covers the crista - cupula.

Front 38

Rotational head movement

Back 38

Endolymph in the membranous semicircular duct is displaced. Pushes the cupula in the opposite direction of the head turn. Stereocilia and kinocilium deflect either causing excitation or inhibition.

Front 39

Linear acceleration

Back 39

Hair cells in the otolith organs are in neuroepithelium called the macula. Stereocilia and kinocilium are located in the otolith membrane. Above this membrane, there are calcium carbonate crystals called otoconia.

Front 40

Otoconia

Back 40

More dense than endolymph and hair cells are displaced by inertia not endolymph.

Front 41

Tip links

Back 41

Staggered height of the stereocilia permits the presence of tip links. Fine strands (possibly elastin) that connect the top of the shorter stereocilium with the lateral wall of its taller neighbor. When the stereocilia are deflected toward the tallest one, opening the "trap door" transduction channels.

Front 42

Scala Media resting potential

Back 42

+ 80-100 mV
Also known as the endocochlear or endolymphatic potential. Generation of the EP is in the stria vascularis.

Front 43

IHCs resting potential

Back 43

-45 mV
When K+ enters the cell and the voltage increases to -20 mV, the cell depolarizes and releases glutamate and aspartate (excitatory neurotransmitters).

Front 44

OHCs resting potential

Back 44

-70 mV

Front 45

Summating potentials

Back 45

A component potential of electrocochleography (ECochG) measured using rarefaction and condensation clicks. Stimulus-related direct current (DC) electrical responses recorded from both the outer and inner hair cells. Some components are thought to be a reflection of the nonlinear distortion in the transduction process. Representative of the stimulus duration.

Front 46

Cochlear microphonic

Back 46

Another component of ECochG. An alternating current (AC) potential that only occurs during the presentation of an acoustic stimulus. This potential appears to mirror the waveform of the acoustic stimulus. The output stems primarily from the OHCs.

Front 47

Action potentials

Back 47

Neural potential: the sum of the potentials of many individual nerve fibers firing synchronously. Similar to the CM, the AP appears to be an AC (alternating current) potential. Reflects the neural output of the cochlea, specifically the AP is associated with wave I of the auditory brainstem response (ABR).

Front 48

Otoacoustic emissions

Back 48

Pre-neural potentials that are acoustic signals detected in the ear canal. These emissions are thought to be echoes that are a result of OHCs contracting to acoustic stimuli. Must do otoscopy and tympanometry!

Front 49

Spontaneous OAEs (SOAEs)

Back 49

OAEs that are measured without any acoustic simulation. We don't know what the absence of OAEs means.

Front 50

Transient Evoked OAEs (TEOAEs)

Back 50

Evoked by click stimuli.

Front 51

Distortion Product OAEs (DPOAEs)

Back 51

Evoked by two pure-tone frequencies.

Front 52

Structure of the auditory nerve

Back 52

Afferent fibers - sensory fibers that carry information from the organ of Corti to the brainstem and brain.
Efferent fibers - bring information from higher neural centers to the auditory periphery.

Front 53

Type I Afferent Nerve Fibers

Back 53

Radial or Type I fibers innervate the IHCs only.
95% of afferent fibers innervate IHCs.
Type I fibers tend to be thicker than Type II fibers.
Convergence: 1 afferent nerve fiber to 1 inner hair cell.

Front 54

Type II Afferent Nerve Fibers

Back 54

Outer spiral or Type II fibers innervate the OHCs.
5% of afferent fibers innervate OHCs.
Divergent: 1 afferent nerve fiber to many hair cells.

Front 55

Efferent nerve fibers

Back 55

Fibers from the lateral superior olive project predominantly to the IHCs. These fibers synapse on the afferent fibers leaving the IHCs. Fibers from the medial superior olive project to the OHCs and these fibers synapse directly on the OHCs.

Front 56

Summary of hair cell function

Back 56

IHCs serve as the main neurologic transducer of acoustic information whereas OHCs serve to maintain and/or alter the biomechanics of the inner ear.

Front 57

Nerve bundle organization

Back 57

Nerve fibers exit the cochlea through the habenula perforata and are organized in a bundle within the modiolus. Fibers from the apex run down the middle and those from the base are on the outside.

Front 58

Single neuron threshold

Back 58

The minimum stimulus level that will cause an increase in the discharge rate above the spontaneous activity.

Front 59

Rate-level functions

Back 59

Increase the level of the acoustic stimulus and measure the change in discharge of a single neuron above the spontaneous rate. All auditory nerve fiber discharge rates increase over a range of 20 to 50 dB (neuronal dynamic range). After the discharge rate will remain the same or decrease slightly when the stimulus level is increased.

Front 60

Response areas

Back 60

Plots each frequency the nerve fiber responds to for a fixed stimulus level. Characteristic frequency - the frequency at which the neuron fires the most.

Front 61

Tuning curve

Back 61

Plot the level of tone required for the neuron to discharge at a threshold amount of firing as a function of the stimulus frequency. Characteristic frequency - the frequency of the neuron's lowest threshold.

Front 62

What do Response Areas and Tuning Curves tell us?

Back 62

Demonstrate that auditory nerve fibers are very selective to frequency. Each fiber fires best to a limited range of frequencies. Maintain the frequency selectivity found along the basilar membrane (tonotopic organization).

Front 63

Histograms

Back 63

Graphic displays of a single neuron's response to repeated presentations of a given stimulus.

Front 64

Phase-locking

Back 64

Occurs when nerve fibers discharge about once per sycle (i.e., 1000 times for a 1000 Hz stimulus). Usually occurs for CFs below 4000 or 5000 Hz.

Front 65

Two-tone suppression

Back 65

Present one tone to auditory nerve fibers that will cause it to fire above its spontaneous rate. Adding a second tone with a certain frequency and level may cause a decrease of suppression in the discharge rate of the fiber to the first tone.

Front 66

The efferent system

Back 66

Research suggests that this system is inhibitory. These inhibitory effects may decrease the neural activity in intense noise situations, protecting the neural system against noise-induced damage. Also may decrease the effect of background noise so you can detect certain desired acoustic signals.

Front 67

Frequency encoding

Back 67

Basilar membrane is tonotopically organized, the afferent auditory nerve innervates the basilar membrane in a systematic way, and as a result the auditory nerve is tonotopically organized. Also called place theory.

Front 68

Intensity encoding

Back 68

Intensity is thought to be encoded by an increase in the discharge rate within the auditory system. Combining low-, medium-, and high- threshold fibers and fibers with different CFs may serve to code for level.

Front 69

Time encoding

Back 69

Aka phase locking
When nerve fibers discharge in synchrony to the phase of the acoustic stimulus, that is what codes the dynamic timing of that stimulus. 5000 Hz is the upper limit where timing codes are effective.