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Questions and Answers
What is the purpose of expressing sound intensities in decibels?
What is the purpose of expressing sound intensities in decibels?
What is the relationship between a 10-fold increase in sound energy and decibels?
What is the relationship between a 10-fold increase in sound energy and decibels?
Which structure do second-order neurons primarily target after synapsing in the cochlear nuclei?
Which structure do second-order neurons primarily target after synapsing in the cochlear nuclei?
What happens to most auditory fibers after synapsing in the inferior colliculus?
What happens to most auditory fibers after synapsing in the inferior colliculus?
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What significant change in sound intensity can the ears barely detect in normal communication?
What significant change in sound intensity can the ears barely detect in normal communication?
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What initiates the fluid wave in the cochlea?
What initiates the fluid wave in the cochlea?
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Which type of wave movement is NOT associated with the basilar membrane?
Which type of wave movement is NOT associated with the basilar membrane?
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How many basilar fibers are present in the basilar membrane?
How many basilar fibers are present in the basilar membrane?
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At what point does the basilar membrane vibrate back and forth with ease?
At what point does the basilar membrane vibrate back and forth with ease?
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What happens to the strength of the wave as it travels along the basilar membrane?
What happens to the strength of the wave as it travels along the basilar membrane?
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Which structure does the basilar membrane separate from the scala tympani?
Which structure does the basilar membrane separate from the scala tympani?
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Which analogy is used to describe the movement of a wave along the basilar membrane?
Which analogy is used to describe the movement of a wave along the basilar membrane?
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What is the primary function of the basilar membrane?
What is the primary function of the basilar membrane?
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What happens to hair cells when the stereocilia bend in one direction?
What happens to hair cells when the stereocilia bend in one direction?
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What is the role of the tectorial membrane in the functioning of hair cells?
What is the role of the tectorial membrane in the functioning of hair cells?
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Where do the auditory nerve fibers synapse in relation to hair cells?
Where do the auditory nerve fibers synapse in relation to hair cells?
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What does bending of the stereocilia in the opposite direction cause?
What does bending of the stereocilia in the opposite direction cause?
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What is primarily transported by the K+ channels involved in hair cell excitation?
What is primarily transported by the K+ channels involved in hair cell excitation?
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Which structure is part of the organ of Corti and plays a crucial role in hearing?
Which structure is part of the organ of Corti and plays a crucial role in hearing?
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What kind of cells are innervated by the cochlear nerve in the organ of Corti?
What kind of cells are innervated by the cochlear nerve in the organ of Corti?
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In which part of the cochlea are the hair cells located?
In which part of the cochlea are the hair cells located?
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What is the primary function of the auditory nerve fibers connected to hair cells?
What is the primary function of the auditory nerve fibers connected to hair cells?
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What physiological change occurs when hair cells are depolarized?
What physiological change occurs when hair cells are depolarized?
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What happens when the basilar membrane moves upward?
What happens when the basilar membrane moves upward?
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Which type of hair cells predominantly transmit auditory signals?
Which type of hair cells predominantly transmit auditory signals?
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What occurs when the stereocilia of hair cells bend toward the longer ones?
What occurs when the stereocilia of hair cells bend toward the longer ones?
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What is the role of the outer hair cells in relation to the inner hair cells?
What is the role of the outer hair cells in relation to the inner hair cells?
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What might occur if the outer hair cells are damaged while the inner hair cells remain functional?
What might occur if the outer hair cells are damaged while the inner hair cells remain functional?
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How does the reticular lamina behave during the downward movement of the basilar membrane?
How does the reticular lamina behave during the downward movement of the basilar membrane?
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What type of channels are involved in the depolarization of hair cells?
What type of channels are involved in the depolarization of hair cells?
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What is the main structure that supports the outer ends of hair cells?
What is the main structure that supports the outer ends of hair cells?
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What role does Ca2+ play in the function of hair cells?
What role does Ca2+ play in the function of hair cells?
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Which statement is true regarding the relationship between the number of hair cells and auditory nerve fibers?
Which statement is true regarding the relationship between the number of hair cells and auditory nerve fibers?
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What happens when low-frequency sounds activate the basilar cilia in the cochlea?
What happens when low-frequency sounds activate the basilar cilia in the cochlea?
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Which ions are primarily responsible for the depolarization of the hair cell membrane?
Which ions are primarily responsible for the depolarization of the hair cell membrane?
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What initiates the depolarization process in hair cells?
What initiates the depolarization process in hair cells?
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What is the place principle in auditory perception?
What is the place principle in auditory perception?
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What occurs when the basilar fibers bend towards the scala vestibuli?
What occurs when the basilar fibers bend towards the scala vestibuli?
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Which part of the cochlea is stimulated by sound frequencies below 200 cycles/sec?
Which part of the cochlea is stimulated by sound frequencies below 200 cycles/sec?
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Which statement accurately describes the process of repolarization in hair cells?
Which statement accurately describes the process of repolarization in hair cells?
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Why are specific brain neurons activated by specific sound frequencies?
Why are specific brain neurons activated by specific sound frequencies?
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How many cation-conducting channels open due to the bending of the stereocilia?
How many cation-conducting channels open due to the bending of the stereocilia?
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What happens to stereocilia when high-frequency sounds are detected?
What happens to stereocilia when high-frequency sounds are detected?
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What is the primary role of the tympanic membrane and ossicular system in hearing?
What is the primary role of the tympanic membrane and ossicular system in hearing?
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How does the sensitivity for hearing change in the absence of the ossicular system?
How does the sensitivity for hearing change in the absence of the ossicular system?
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What is the role of the tensor tympani muscle during loud sounds?
What is the role of the tensor tympani muscle during loud sounds?
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Which membranes separate the scala vestibuli and scala media in the cochlea?
Which membranes separate the scala vestibuli and scala media in the cochlea?
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What occurs within the organ of Corti when sound vibrations are detected?
What occurs within the organ of Corti when sound vibrations are detected?
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Where in the cochlea does low-frequency resonance primarily occur?
Where in the cochlea does low-frequency resonance primarily occur?
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What initial effect does sound wave entry at the oval window have on the basilar membrane?
What initial effect does sound wave entry at the oval window have on the basilar membrane?
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What is the role of the round window in response to sound waves entering the cochlea?
What is the role of the round window in response to sound waves entering the cochlea?
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How does high-frequency resonance differ from low-frequency resonance in the cochlea?
How does high-frequency resonance differ from low-frequency resonance in the cochlea?
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What primarily influences the movement of the basilar membrane when sound waves are present?
What primarily influences the movement of the basilar membrane when sound waves are present?
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What is the primary characteristic of the basilar fibers in the basilar membrane?
What is the primary characteristic of the basilar fibers in the basilar membrane?
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How does the strength of the fluid wave change as it travels along the basilar membrane?
How does the strength of the fluid wave change as it travels along the basilar membrane?
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What aspect of the basilar membrane relates it to the movement of a pressure wave along arterial walls?
What aspect of the basilar membrane relates it to the movement of a pressure wave along arterial walls?
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What portion of the cochlea contains the structure known as the modiolus?
What portion of the cochlea contains the structure known as the modiolus?
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What happens to the energy in the wave as it reaches the portion of the basilar membrane with a natural resonant frequency?
What happens to the energy in the wave as it reaches the portion of the basilar membrane with a natural resonant frequency?
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Which frequency of sound activates the lower parts of the basilar membrane?
Which frequency of sound activates the lower parts of the basilar membrane?
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What is the role of the basilar membrane in relation to sound waves?
What is the role of the basilar membrane in relation to sound waves?
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What does the comparison between wave movements in the cochlea and waves on a pond emphasize?
What does the comparison between wave movements in the cochlea and waves on a pond emphasize?
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Which of the following best describes the pattern of transmission for sound waves with varying frequencies along the basilar membrane?
Which of the following best describes the pattern of transmission for sound waves with varying frequencies along the basilar membrane?
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What initiates the initial fluid wave within the cochlea?
What initiates the initial fluid wave within the cochlea?
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The malleus is connected to the incus by large ligaments.
The malleus is connected to the incus by large ligaments.
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The stapes causes the round window to push on the cochlear fluid when the tympanic membrane moves inward.
The stapes causes the round window to push on the cochlear fluid when the tympanic membrane moves inward.
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The tensor tympani and stapedius muscles help reduce sensitivity to external sounds.
The tensor tympani and stapedius muscles help reduce sensitivity to external sounds.
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The tensor tympani muscle pulls forward on the malleus when activated.
The tensor tympani muscle pulls forward on the malleus when activated.
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Movement of the tympanic membrane does not affect the stapes.
Movement of the tympanic membrane does not affect the stapes.
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The tympanic membrane and ossicular system provide an impedance matching that is 100% perfect for sound frequencies between 300 and 3000 cycles/sec.
The tympanic membrane and ossicular system provide an impedance matching that is 100% perfect for sound frequencies between 300 and 3000 cycles/sec.
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In the absence of the ossicular system, hearing sensitivity decreases by 15 to 20 decibels.
In the absence of the ossicular system, hearing sensitivity decreases by 15 to 20 decibels.
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The cochlea consists of two tubes coiled side by side.
The cochlea consists of two tubes coiled side by side.
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The contraction of the tensor tympani muscle has no effect on sound transmission.
The contraction of the tensor tympani muscle has no effect on sound transmission.
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The organ of Corti is located on the surface of the basilar membrane and contains sensitive hair cells.
The organ of Corti is located on the surface of the basilar membrane and contains sensitive hair cells.
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The stereocilia attached to hair cells are flexible structures due to their protein framework.
The stereocilia attached to hair cells are flexible structures due to their protein framework.
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The tops of the hair cells in the ear are bathed in endolymph, while the lower bodies are surrounded by perilymph.
The tops of the hair cells in the ear are bathed in endolymph, while the lower bodies are surrounded by perilymph.
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A negative intracellular potential of −150 millivolts is found at the upper surfaces of hair cells.
A negative intracellular potential of −150 millivolts is found at the upper surfaces of hair cells.
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The outer hair cells can shorten when stimulated by retrograde nerve fibers.
The outer hair cells can shorten when stimulated by retrograde nerve fibers.
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Hair cells have roughly 50 stereocilia projecting from each cell's apical border.
Hair cells have roughly 50 stereocilia projecting from each cell's apical border.
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The high electrical potential at the tips of the stereocilia enhances their ability to respond to sound.
The high electrical potential at the tips of the stereocilia enhances their ability to respond to sound.
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The endocochlear potential is irrelevant in determining the sensitivity of hair cells.
The endocochlear potential is irrelevant in determining the sensitivity of hair cells.
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Stimulation of the hair cell stereocilia results in the release of an inhibitory neurotransmitter.
Stimulation of the hair cell stereocilia results in the release of an inhibitory neurotransmitter.
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Hair cells can become increasingly stiff in response to different sound pitches.
Hair cells can become increasingly stiff in response to different sound pitches.
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Stereocilia become shorter on the side of the hair cell that is closest to the modiolus.
Stereocilia become shorter on the side of the hair cell that is closest to the modiolus.
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Match the components of the auditory system with their functions:
Match the components of the auditory system with their functions:
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Match the potential differences with their locations in hair cells:
Match the potential differences with their locations in hair cells:
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Match the hair cell structures with their characteristics:
Match the hair cell structures with their characteristics:
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Match the auditory nerve components with their roles:
Match the auditory nerve components with their roles:
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Match the cellular mechanisms with their effects on sound detection:
Match the cellular mechanisms with their effects on sound detection:
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Match the following components of the organ of Corti with their functions:
Match the following components of the organ of Corti with their functions:
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Match the following structures with their associated ions in hair cell excitation:
Match the following structures with their associated ions in hair cell excitation:
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Match the following actions with their outcomes related to hair cells:
Match the following actions with their outcomes related to hair cells:
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Match the following functions with their corresponding cells in the cochlea:
Match the following functions with their corresponding cells in the cochlea:
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Match the following parts of the cochlea with their roles in auditory perception:
Match the following parts of the cochlea with their roles in auditory perception:
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Study Notes
The Inner Ear
- The cochlea is a fluid-filled, spiral-shaped organ that houses the organ of Corti.
- Fluid waves travel along the basilar membrane within the cochlea.
- The basilar membrane is a fibrous, elastic membrane that separates the scala media from the scala tympani.
- The basilar membrane contains 20,000 to 30,000 basilar fibers that project from the modiolus towards the outer wall.
- Basilar fibers are stiff, elastic, reed-like structures with varying lengths and stiffness across the membrane.
Vibration Patterns of the Basilar Membrane
- The basilar membrane vibrates in response to fluid waves generated by stapes movement.
- Different frequencies of sound waves cause different patterns of vibration along the basilar membrane.
- High-frequency sounds cause maximal vibrations at the base of the basilar membrane near the oval window.
- Low-frequency sounds cause maximal vibrations at the apex (helicotrema) of the basilar membrane.
- The resonance frequency of the basilar membrane is dependent on the stiffness and length of its fibers.
The Organ of Corti
- The organ of Corti is located on the basilar membrane and is the sensory organ of hearing.
- It contains specialized hair cells that are responsible for converting mechanical vibrations into neural signals.
- Hair cells have stereocilia that extend from their apical surface and are embedded into the tectorial membrane, a gelatinous structure overlying the organ of Corti.
Sound Transduction
- Hair cell bending in one direction depolarizes the hair cell, while bending in the opposite direction hyperpolarizes it.
- When the basilar membrane vibrates, the hair cells are bent, causing the opening of potassium channels in the stereocilia.
- The influx of potassium ions into the hair cell causes depolarization, which triggers the release of neurotransmitters at the base of the hair cell.
- The neurotransmitters stimulate auditory nerve fibers, which transmit the signal to the brain.
Sound Intensity and Frequency Coding
- The intensity of sound is determined by the amplitude of the vibration of the basilar membrane.
- The frequency of sound is determined by the location on the basilar membrane that is most strongly vibrated.
- The place principle for the determination of sound frequency refers to the fact that different frequencies activate specific regions of the basilar membrane.
- The auditory pathway from the cochlea to the cerebral cortex maintains a tonotopic organization, meaning that neurons responding to specific frequencies remain organized in a specific pattern along the pathway.
Auditory Pathway
- Auditory nerve fibers from the spiral ganglion of Corti project to the cochlear nuclei in the medulla.
- From the cochlear nuclei, second-order neurons project to the superior olivary nucleus (SON) on both sides of the brainstem.
- The auditory pathway then continues through the lateral lemniscus, the inferior colliculus, and the medial geniculate nucleus before reaching the auditory cortex in the temporal lobe.
- The auditory cortex is where more complex auditory information is processed and interpreted.
- The auditory cortex is located in the superior gyrus of the temporal lobe.
Sound Intensity
- Sound intensity is measured in decibels (dB).
- A 10-fold increase in sound energy corresponds to a 1 bel increase, which is equivalent to 10 decibels.
- The human ear can detect a very wide range of sound intensities.
- The decibel scale is logarithmic, meaning that a small increase in decibels represents a large increase in sound energy.
- The threshold for hearing sound varies with frequency.
Impedance Matching
- Tympanic membrane and ossicular system act as an impedance matching system between air and fluid in the cochlea.
- This system effectively matches sound waves in air to sound vibrations in the cochlear fluid, allowing for approximately 50% to 75% efficiency in the frequency range of 300 to 3000 cycles/second.
The Cochlea
- The cochlea is a fluid-filled, coiled structure crucial for hearing.
- It comprises three fluid-filled tubes: scala vestibuli, scala media, and scala tympani.
- Reissner's membrane separates scala vestibuli and scala media, while the basilar membrane separates scala tympani and scala media.
- The organ of Corti, located on the basilar membrane, contains hair cells, the sensory receptors for sound.
Sound Transmission in the Cochlea
- Stapes movement against the oval window generates pressure waves in the cochlea, causing the basilar membrane to vibrate.
- This vibration creates a "traveling wave" along the membrane, with different frequencies resonating at specific locations.
- High frequencies resonate near the base of the cochlea, while low frequencies resonate near the helicotrema.
Basilar Membrane Resonance
- The basilar membrane is a flexible structure composed of fibers of varying stiffness and width.
- Stiffer fibers vibrate at higher frequencies, while the wider and more flexible fibers resonate at lower frequencies.
Auditory Pathway
- Auditory nerve fibers from the hair cells of the organ of Corti transmit signals to the cochlear nuclei in the medulla.
- From the cochlear nuclei, second-order neurons primarily project to the superior olivary nucleus on the opposite side of the brainstem.
- The auditory pathway continues through the lateral lemniscus to the inferior colliculus, where most auditory fibers synapse.
- The pathway then ascends to the medial geniculate nucleus, where all auditory fibers synapse.
- Finally, the pathway projects to the auditory cortex in the temporal lobe.
Sound Intensity
- Sound intensity is measured in decibels (dB), a logarithmic scale representing a 10-fold increase in energy for every 10 dB increase.
- The ear can perceive a change of approximately 1 dB in sound intensity.
Hearing Threshold
- The minimum sound pressure required to elicit a response in the ear is known as the hearing threshold.
- Hearing threshold varies with frequency, with the human ear most sensitive to sounds between 2000 and 5000 Hz.
Middle Ear
- Malleus, incus, and stapes are the three bones in the middle ear
- The malleus is connected to the incus by ligaments
- The incus articulates with the stapes
- The stapes pushes forward on the oval window when the incus moves forward
- The stapes pulls backward on the oval window when the incus moves backward
- The tympanic membrane and ossicular system help to match impedance between sound waves in air and sound vibrations in the fluid of the cochlea
- The ossicular system provides impedance matching of about 50-75% for sound frequencies between 300 and 3000 cycles/sec
Cochlea
- The cochlea is a coiled tube consisting of three tubes: scala vestibuli, scala media, and scala tympani
- The scala vestibuli and scala media are separated by Reissner’s membrane
- The scala tympani and scala media are separated by the basilar membrane
- The organ of Corti contains hair cells which are the receptive end organs that generate nerve impulses in response to sound vibrations
- The endolymph in the scala media contributes to the high electrical potential of the hair cells
Sound Frequency Determination
- The place principle is used by the nervous system to detect different sound frequencies
- Low-frequency sounds activate the basilar membrane near the apex of the cochlea
- High-frequency sounds activate the basilar membrane near the base of the cochlea
- Intermediate-frequency sounds activate the membrane at intermediate distances between the two extremes
Auditory Pathways
- The auditory pathways from both ears are transmitted through the pathways of both sides of the brain, with a preponderance of transmission in the contralateral pathway
- Crossing over between the two pathways occurs in three places in the brain stem
- Many collateral fibers from the auditory tracts pass directly into the reticular activating system of the brain stem
Neural Firing Rate
- Single nerve fibers entering the cochlear nuclei from the auditory nerve can fire at rates up to at least 1000/sec
- The firing rate is determined mainly by the loudness of the sound.
The Organ of Corti and Hair Cells
- The organ of Corti contains hair cells, which are responsible for the sense of hearing
- Hair cells are located in the scala media between the tectorial membrane and the basilar membrane
- The tectorial membrane presses against the stereocilia (hairs) on the hair cells
- Bending of the stereocilia in one direction depolarizes the hair cells, and bending in the opposite direction hyperpolarizes them
- This bending of the stereocilia is caused by vibrations in the basilar membrane
- Depolarization of hair cells leads to the release of glutamate, an excitatory neurotransmitter, which excites the auditory nerve fibers
- The endolymph has a high electrical potential, which sensitizes the hair cells and increases their ability to respond to sound
The Place Principle and Determination of Sound Frequency
- The place principle explains how the brain determines the frequency of a sound
- Different frequencies of sound cause different parts of the basilar membrane to vibrate
- Higher frequency sounds cause vibrations closer to the oval window
- Lower frequency sounds cause vibrations farther away from the oval window
- The hair cells that are stimulated by the vibrations in the basilar membrane send signals to the brain
- Different hair cells send signals for different frequencies, so the brain can decode the frequency of the sound
- This allows the ear to detect a wide range of sound intensities
The Auditory Pathway
- The auditory nerve fibers from the spiral ganglion of Corti synapse in the cochlear nuclei in the medulla
- Second-order neurons from the cochlear nuclei mainly cross to the opposite side of the brainstem and travel to the superior olivary nucleus
- The auditory pathway then ascends through the lateral lemniscus to the inferior colliculus
- From the inferior colliculus, the pathway goes to the medial geniculate nucleus
- The auditory pathway finally reaches the auditory cortex, which is located in the superior gyrus of the temporal lobe
Sound Localization
- Sound localization relies on the difference in the time of arrival of sound waves at each ear
- Neurons in the medial superior olivary nucleus are sensitive to these time differences
- When a sound comes from directly in front of the head, there is no time lag
- When a sound comes from a specific location, one ear hears the sound slightly before the other
- The medial superior olivary nucleus uses these time differences to determine the direction of the sound
Auditory Cortex
- The auditory cortex is responsible for processing and interpreting sound information
- Lesions of the auditory cortex can impair the ability to discriminate and understand sound patterns
- The auditory association areas help interpret the meaning of sounds
Audiometer and Hearing Tests
- An audiometer is used to measure hearing ability
- An audiometer emits pure tones of different frequencies and intensities
- The volume control on the audiometer is calibrated so that zero decibels represent the level of sound that a normal ear can just barely hear
- A hearing loss is defined as the number of decibels above normal that a sound must be increased for it to be heard
- Hearing tests are used to evaluate the different frequencies of sound a person can hear
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Description
Explore the fascinating structures of the inner ear, including the cochlea and basilar membrane. This quiz covers the mechanics of sound vibrations and how they affect our hearing. Test your knowledge on the roles of fluid waves and vibration patterns in auditory perception.
