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Questions and Answers
What is the primary function of the pinna in sound localization?
What is the primary function of the pinna in sound localization?
How much does the external auditory canal amplify sound pressure?
How much does the external auditory canal amplify sound pressure?
What role do the ossicles play in the middle ear?
What role do the ossicles play in the middle ear?
What is the purpose of the stapes in the middle ear?
What is the purpose of the stapes in the middle ear?
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What factor complicates the conversion of airborne pressure waves into pressure waves in the fluid-filled inner ear?
What factor complicates the conversion of airborne pressure waves into pressure waves in the fluid-filled inner ear?
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What attribute of sound is determined by the frequency of pressure changes?
What attribute of sound is determined by the frequency of pressure changes?
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Which range of frequencies is considered audible for humans?
Which range of frequencies is considered audible for humans?
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How does the auditory system identify the location of a sound?
How does the auditory system identify the location of a sound?
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What is the primary function of the external ear?
What is the primary function of the external ear?
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Which statement about pure tones and natural sounds is true?
Which statement about pure tones and natural sounds is true?
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What does the term 'detection threshold' refer to in the context of sound?
What does the term 'detection threshold' refer to in the context of sound?
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How does age affect an individual's ability to hear?
How does age affect an individual's ability to hear?
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What mathematical technique is used to break down complex sounds into pure tones?
What mathematical technique is used to break down complex sounds into pure tones?
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What is the primary mechanism for sound localization of low-frequency sounds?
What is the primary mechanism for sound localization of low-frequency sounds?
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How do high-frequency sound sources influence auditory nerve neurons?
How do high-frequency sound sources influence auditory nerve neurons?
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Where is the primary auditory cortex located?
Where is the primary auditory cortex located?
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What occurs in the superior olive related to auditory processing?
What occurs in the superior olive related to auditory processing?
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What is the role of phase locking in low-frequency-tuned neurons?
What is the role of phase locking in low-frequency-tuned neurons?
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Which component of the auditory pathway generates a topographical representation of auditory space?
Which component of the auditory pathway generates a topographical representation of auditory space?
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What happens to neurons tuned to high frequencies, specifically over 2 kHz?
What happens to neurons tuned to high frequencies, specifically over 2 kHz?
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Which of the following accurately describes neurons tuned to low frequencies?
Which of the following accurately describes neurons tuned to low frequencies?
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What occurs when the basilar membrane is deflected upwards?
What occurs when the basilar membrane is deflected upwards?
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How does depolarization of the hair cells occur?
How does depolarization of the hair cells occur?
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What is the effect of bending the stereocilia in the opposite direction?
What is the effect of bending the stereocilia in the opposite direction?
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What characterizes the receptor potentials generated by hair cells?
What characterizes the receptor potentials generated by hair cells?
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What triggers the release of the neurotransmitter glutamate at synapses with sensory afferents?
What triggers the release of the neurotransmitter glutamate at synapses with sensory afferents?
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What type of channels are found in stereocilia?
What type of channels are found in stereocilia?
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Which statement is true regarding inner hair cells?
Which statement is true regarding inner hair cells?
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What ion is primarily involved in the depolarization of hair cells?
What ion is primarily involved in the depolarization of hair cells?
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What structural feature connects the mechanically gated cation channels in stereocilia?
What structural feature connects the mechanically gated cation channels in stereocilia?
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What is the role of outer hair cells in the auditory system?
What is the role of outer hair cells in the auditory system?
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What is the result of glutamate binding to ionotropic receptors on sensory afferents?
What is the result of glutamate binding to ionotropic receptors on sensory afferents?
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Why do hair cells not generate action potentials?
Why do hair cells not generate action potentials?
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Which feature differentiates outer hair cells from inner hair cells?
Which feature differentiates outer hair cells from inner hair cells?
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What physiological change occurs in outer hair cells during depolarization?
What physiological change occurs in outer hair cells during depolarization?
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What is a function of otoacoustic emissions generated by outer hair cells?
What is a function of otoacoustic emissions generated by outer hair cells?
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The influx of which ion is primarily responsible for the activation of voltage-gated channels at synapses?
The influx of which ion is primarily responsible for the activation of voltage-gated channels at synapses?
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Which fluid is found in the scala media?
Which fluid is found in the scala media?
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What is the primary function of the hair cells in the Organ of Corti?
What is the primary function of the hair cells in the Organ of Corti?
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What structure separates the scala tympani from the scala media?
What structure separates the scala tympani from the scala media?
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Which type of cells form a single row within the Organ of Corti?
Which type of cells form a single row within the Organ of Corti?
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What connects the basilar membrane to the modiolus?
What connects the basilar membrane to the modiolus?
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What type of neurons form synapses with the hair cells of the Organ of Corti?
What type of neurons form synapses with the hair cells of the Organ of Corti?
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Which cranial nerve contains the auditory information from the cochlea?
Which cranial nerve contains the auditory information from the cochlea?
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The apical processes of hair cells are known as what?
The apical processes of hair cells are known as what?
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Study Notes
Auditory System Overview
- The auditory system comprises the external, middle, and inner ear, and central processing areas.
- Lecture topics cover sound transmission, sound transduction, and central processing.
Sound & Its Transmission in the External and Middle Ear
- Sound is a wave of compressed and rarified air, represented by a sinusoidal function.
- Sound waves are generated by vibrating objects and propagate in three dimensions.
- Wave amplitude determines loudness, and frequency determines pitch.
- Two waves of the same pitch can differ in phase (timing of peaks and troughs), relevant for sound localization.
- The external ear (pinna and auditory canal) funnels sound waves to the tympanic membrane, amplifying sound pressure 30-100 fold.
- The middle ear (ossicles: malleus, incus, stapes) transmits vibrations to the oval window.
- Vibration of the tympanic membrane moves the ossicles, amplifying pressure.
- Stapes transmits vibrations to oval window, and conversion of airborne pressure waves into pressure waves in the fluid-filled inner ear occurs.
Regulation of Sound Transmission Efficiency
- The inner ear is vulnerable to damage, especially from loud noises.
- Reflex responses, like tensor tympani and stapedius muscle contractions, dampen sound transmission efficiency.
- Muscles help protect the ear from damage caused by loud noises
- Flexion of the tensor tympani and stapedius muscles reduces movement of the stapes.
- Reduction in vibrations from loud noises, via contraction of these muscles.
Sound Transduction in the Inner Ear
- Cochlear ducts are fluid-filled channels in the cochlea, including scala vestibuli, scala tympani, and scala media.
- Oval window connects to scala vestibuli, the round window connects to scala tympani.
- Basilar membrane plays a key role in sound transduction by vibrates in response to sound pressure waves based on frequency.
- Organ of Corti contains hair cells.
- The organ of Corti has inner hair cells and outer hair cells, which convert sound vibrations into electrical signals.
- Sensory neurons carry this information to the central auditory system.
Sound Transmission in the Cochlea
- Vibration of the oval window creates pressure waves in the perilymph of the scala vestibuli and then scala tympani
- Pressure waves cause displacement of the basilar membrane
- Basilar membrane properties vary over length of cochlea (narrow and stiff at the base, wide and floppy at the apex).
- Placement of movement in the basilar membrane depending on frequency of sound: High-frequency sounds at base; low-pitched at apex.
- Tonotopy: topographical mapping of sound frequency onto the basilar membrane.
Sound Transmission: Organ of Corti
- Movement of the basilar membrane causes movement of the tectorial membrane which in turn causes the stereocilia to move
- This bending results in stereocilia of hair cells to being bent away from the center of the cochlea.
- Conversely, downward bending causes the bending of stereocilia in the other direction.
- Vibration translated to back and forth motion of hair cell stereocilia
Sound Transduction Receptor Potentials and Molecular Mechanisms
- Deflection of hair cell stereocilia generates receptor potentials (mechanical stimuli to electrical stimulus).
- Larger deflection of cilia leads to larger depolarization..
- Bending of cilia in either direction changes the membrane potential.
- Bending of cilia towards stereocilia cause depolarization; away causes hyperpolarization.
- Membrane depolarization opens calcium channels, which release glutamate.
- This triggers the opening of ion channels, initiating a nerve impulse.
- This creates nerve impulse via ionotropic glutamate receptors on sensory afferents causing depolarization in sensory neurons and action potentials in sensory neurons
Functional Differences Between Inner and Outer Hair Cells
- Inner hair cells receive 95% of sensory innervation.
- Outer hair cells receive efferents from the superior olivary complex in the brainstem.
- Outer hair cells can rapidly alter their length, amplifying the basilar membrane's response (cochlear amplifier).
- Vibrations generate otoacoustic emissions.
Hearing Loss: Causes and Treatment
- Conductive hearing loss affects external or middle ear.
- Sensorineural hearing loss involves inner ear damage.
- Causes: occlusion, rupture (external/middle), hair cell death.
- Diagnosis: Weber and Rinne tests.
- Conductive hearing loss: sound conducted through bones (not through air),
- Sensorineural hearing loss: Sound is not conducted through bones.
- Treatment: external hearing aids, bone-anchored hearing aids, and cochlear implants.
Central Processing of Auditory Information
- Bipolar neurons form the auditory nerve, with cell bodies in spiral ganglion.
- Neurons in the ventral and dorsal cochlear nuclei, project bilaterally to the superior olive (important for sound localization).
- Neurons in the superior olive and dorsal cochlear nucleus project to the inferior colliculus.
- Neurons in the inferior colliculus project to the medial geniculate nucleus in the thalamus.
- Neurons in the medial geniculate nucleus project to the primary auditory cortex.
- Primary auditory cortex (AI) receives projections from the medial geniculate nucleus and has tonotopic organization; also receive projections from one side and inhibition from other side (temporal order important).
- Secondary auditory cortex (AII) surrounds primary auditory cortex; involved in sound location.
- Belt and parabelt areas are also part of the auditory cortex.
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Description
Explore the structure and function of the auditory system, focusing on the external, middle, and inner ear. This quiz covers sound transmission, wave properties, and the mechanics of hearing. Test your knowledge on how sound is processed and localized by the ear.
