Term
| What are the three major parameters of sound waves? |
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Definition
| Waveform frequency, waveform shape, and waveform amplitude. |
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Term
| What does the ear interpret these parameters as? |
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Definition
Frequency= pitch
Shape= tone or timbre
Amplitude= loudness |
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Term
| What is the hearing range of humans, prior to damage? What are sounds above this range called? Below? |
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Definition
20-20,000 Hz
Ultrasound
Infrasound |
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Term
| How is loudness measured? Describe how the scale works |
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Definition
| Decibels. The scale is logarithmic. Sounds that differ in loudness by one order of magnitude differ by 20 dB |
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Term
| True/False- Negative decibels exist |
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Definition
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Term
| True/False- Humans cannot hear a sound of 0 dB |
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Definition
| False- 0 dB is barely perceptible |
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Term
| What effects the amount of damage a sound does to the ear? |
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Definition
| The loudness (dB) and duration of exposure. |
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Term
| How is the direction of a sound determined? |
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Definition
| The latency (time difference) and difference in loudness between each ear |
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Term
| What 2 major roles does the outer ear play in hearing? |
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Definition
Amplification
Localization |
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Term
| Describe how the outer ear amplifies sound? |
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Definition
Amplification- outer ear acts as both a funnel and a resonator
Funnel-the pinna collects sound from a wider area which is directed into the narrower auditory canal
Resonator- the outer ear acts a resonator for sounds within the frequency range of the human voice. |
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Term
| How does the outer ear contribute to sound localization? |
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Definition
| Localization- pinna contributes to localization of sounds differing in vertical direction--the mechanism is not well understood |
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Term
| What is the major role of the middle ear? |
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Definition
The middle ear functions in
impedance matching
attenuation reflex |
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Term
| Describe impedance matching. Why is it necessary? |
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Definition
| Impedance matching is the middle ear mathcing the movement of air in the middle ear to the movement of fluid in the inner ear. This is important because the fluid which fills the inner ear has a greater resistance to motion than the air of the middle ear. occurs when the middle ear |
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Term
| What are the mechanisms by which impedance matching works? |
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Definition
-Surface area differance between the large tympanic membrane and the smaller oval window which concentrates the force of the sound waves onto a small area increasing the pressure applied to the fluid of the inner ear.
- ossicles of the middle ear act as a lever helping to transform larger amplitude, lower force vibrations of the air to smaller amplitude, higher force vibrations of the air to smaller amplitude, higher force vibrations of the fluid of the inner ear. |
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Term
| Describe the attenuation reflex |
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Definition
The attenuation reflex protects the ears from loud or damaging sounds, enjances high frequency sound in an environment of low frequency sound, suppresses the apparent loudness of our own voice.
This is doens by two muscle that attach the the ossicles, the tensor tympani and the stapedius. Loud sounds cause these muscles to contracts, increasing the rigidity of the ossicles and reducing sound conduction to the inner ear. |
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Term
| Describe where and how conduction deafness can occur. |
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Definition
Outer ear-obstructions in the auditory canal.
Middle ear- fluid build up due to cold or infection. Damage to the ossicles or abnormal tissue growth in the middle ear |
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Term
| What is abnormal tissue growth in the middle ear called? |
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Definition
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Term
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Definition
| Middle ear infection, leads to fluid/pus accumulation |
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Term
| What is the major role of the inner ear? |
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Definition
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Term
| How does auditory transduction take place? |
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Definition
Vibrations are trnasduced into fluid waves
Then movements of the basilar membrane this causes hair cell depolarization and hyperpolarization, and finally into patterns of action potential firing the afferent nerve. |
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Term
| How does fluid wave formation lead to the firing of afferent nerve fibers? |
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Definition
| The stapes vibrates on the oval window. This causes the perilymph in the scala vestibuli to push down on Reisner's membrane. This compresses endolymph (of the scala media), which in turn moves the basilar membrane. Movement of the basilar displaces hair cell cillia bending them against the tectorial causing them to depolarize and hyperpolarize. |
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Term
| How is the pressure of the fluid in the cochlea releived? |
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Definition
| The outward movement of the round window. |
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Term
| Describe the shape and any distinctions of the basilar membrane. |
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Definition
| The basilar membrane is narrower and stiffer at the base, near the oval and round window. It is wider and looser at the apex which contains the helicotrema. |
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Term
| What area of the basilar membrane would a high frequency sound wave cause the most movement in? |
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Definition
| The base, near the oval and round window. |
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Term
| What area of the basilar membrane would a low frequency sound move? |
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Definition
| The apex near the helicotrema. |
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Term
| True/False The basilar membrane is tuned so that different locations along the membrane vibrate maximally at specific frequencies. |
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Definition
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Term
| What causes hairs cells of the ear depolarize? |
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Definition
| Bending toward the kinocillium allowing fot eh opening of mechanically gated ion channels which then lets potasium and calcium in. |
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Term
| True/False Hair cells only release NT when they are depolarized. |
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Definition
| False. Hair cells are always releasing a tonic level of NT. The bending of hair cells stereocili cause alternating depolorization and hyperpolorization of the hair cell, corresponding to an increase and decreasee in transmitter relase and a coresponding increase and decrease in firing in afferent nerve fibers innervating the hair cells. |
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Term
| What are the different types of hair cells? |
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Definition
| Inner hair cells and outter hair cells. |
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Term
| What is the function of outer hair cells and how is this accomplished |
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Definition
| Outer hair cells allow for cochlear amplification. Prestin, a motor protein, causes the hair cells to change length according to membrane potential. Depolarization causes prestin to contract pulling the tectorial membrane closer to the basilar membrane, which increases the bending of the basilar membrane and increasing the response of the inner hair cells. |
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Term
| True/False The ear produces sound |
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Definition
| True. Contractions of the outer hair cells are responsible for otoacoustic emissions--sounds that can be recorded by a small microphone place in the auditory canal. |
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Term
| What is the purpose of cochlear amplification by outer hair cells? |
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Definition
| To improve the sensitivity and frequency selectivity of inner hair cells |
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Term
| What mechanisms contribute to sound frequency discrimination? |
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Definition
-Resonate properties of the basilar membrane
-motor function of the outer hair cell
-stiffness of hair cell cilia vary depending on the location of hair cells in the basilar membrane in a way which complements the systematic variation in stiffness of the basilar membrane
-electrical resonance- property displayed by the basolateral membrane of hair cells, when depolarized the membrane potential oscillates at a specific frequency that varies systematically along the basilar membrane. |
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Term
| What are the two ways sound intensity is encoded? |
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Definition
| Increase in the number of action potentials fired in individual afferent fibers and an increase int he number of afferent fibers firing action potentials. |
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Term
| What are two ways sound frequency is encoded? |
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Definition
Tonotopic representation
Phase locking |
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Term
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Definition
| Inner hair cells fire at specific frquencies depending on their location along the basilar membrane. Consequently, auditory afferent fibers fire at characteristic frequencies that vary with the location of their innervation of the basilar membrane. |
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Term
| Where are tonotopic representations maitained? |
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Definition
| Auditory relay nuclei, medial geniculate nucleus, and auditory cortex. |
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Term
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Definition
| Phase locking refers to the consistent relationship between action potential firing in an auditory nerve fiber and the phase of the sound wave. |
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Term
| Describe phase locking at low frequencies. |
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Definition
| Firing occurs precisely aligned with each sound wave. |
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Term
| Describe phase locking at intermediate frequencies. |
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Definition
| Sound waves occur at an interval shorter than the absolute refractory period and volley coding becomes prominent. |
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Term
| At what point does phase locking no longer occur? |
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Definition
| Frequencies above 4,000 Hz. THe intervals between sound waves are very short and auditory afferent can no longer fire in phase with sound waves. Sound is represented solely by tonotopy. |
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Term
| How do we know tonotopic coding is not the only mechanism by which frequency coding occurs? |
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Definition
1. There is little difference in the portion of the basilar membrane activated by frequencies between 50-200Hz. We can discriminate frequencies within this range so there must be another mechanism
2. The extent of the basilar membrane activation varies with both frequency and intensity. |
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Term
| How do we localize horizontal sounds? |
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Definition
Interaural time delay for sounds below 2,000 Hz.
Interaural intensity differences for sounds about 2,000 Hz. |
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Term
| At what frequency is interaural time delay ambiguous? Why? |
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Definition
| Frequencies greater than 2,00 Hz. The distance between sound wave peaks has become smaller than the distance between the ears. |
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Term
| Where are the neurons located that are responsible for detecting interaural time differences? |
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Definition
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Term
| Where are neurons located that are responsible for determining horizontal sound localization by differences in intensity? |
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Definition
| The lateral superior olive |
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Term
| What is the mechanism for vertical sound localization? |
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Definition
| Not well understood. Has to do with the folds and curves in the pinna of the outer ear. High sound frequencies enter the auditory canal more efficiently from above than from below. |
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Term
| How does nerve deafness occur (Mechanism)? |
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Definition
| Results form damage to the cochlear hair cells or the afferent nerve fibers. Conduction from outer and middle ear is intact but pressure waves cannot be transduced into electrical nerve activity. |
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Term
| What are some causes of nerve deafness? |
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Definition
Hereditary-variety of genetic disorders resulting in the improper formation of the middle ear. Prenatal exposure to rubella, influenza, mumps, methyl mecury, quinine.
Environmental causes such as loud music or loud work environment. |
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Term
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Definition
| Progressive hearing loss. |
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