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Questions and Answers
What is defined as the number of cycles per second expressed in hertz (Hz)?
What is the range of human hearing in hertz?
At which frequencies are humans most sensitive to sound?
What factor primarily determines the loudness of sound?
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What is the threshold of pain in decibels (dB)?
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Which term best describes a sound made up of only one frequency?
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What is the primary role of cochlear hair cells in hearing?
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What is the relationship between wavelength and frequency in sound?
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What aspect of sound intensity encoding is correlated with perceived loudness?
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Which mechanism is primarily responsible for localizing low frequency sounds?
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How are high frequency sounds primarily localized?
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What does the coincidence detection principle require for sound localization?
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What role does tonotopy play in the auditory system?
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What characterizes the primary auditory cortex (A1) in terms of neuronal organization?
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Which of the following conditions can result in almost normal auditory function despite a unilateral lesion?
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What characteristic of hair cells affects the encoding of stimulus intensity in sound?
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What is the significance of phase locking for sound processing?
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Which frequency range is primarily associated with duplex theory for sound localization?
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What role does the auditory association area play in sound perception?
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Which condition describes a blockage that prevents sound from reaching the inner ear fluids?
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Which of the following is a common cause of sensorineural deafness?
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What is a primary cause of tinnitus?
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How do cochlear implants assist deaf patients?
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What do vestibular receptors primarily monitor?
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What excites the crista ampullaris during motion?
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Which structure houses the receptors for detecting rotational acceleration?
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What happens to hair cells in the crista ampullaris when they are bent in one direction?
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How do the semicircular canals contribute to balance?
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What characteristic of fibers near the oval window of the basilar membrane allows them to resonate with high-frequency waves?
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How does the basilar membrane contribute to the mechanical processing of sound?
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What is the function of the outer hair cells in the ear?
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Why do nerve fibers coiled around outer hair cells convey messages from the brain to the ear?
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How does sound localization occur in the auditory system?
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What triggers the release of neurotransmitter in hair cells during sound transduction?
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What kind of response properties can be observed in neurons beyond the brain stem?
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Which structure serves as the auditory reflex center in the neural pathway from cochlear bipolar cells to the auditory cortex?
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What determines the perception of loudness in auditory processing?
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What is meant by 'characteristic frequency' in auditory neurons?
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What is the role of the auricle in the auditory system?
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Which component serves as the boundary between the external and middle ears?
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What happens to the ion channels in stereocilia when they bend away from the tallest ones?
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What is the function of the tensor tympani and stapedius muscles in the middle ear?
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What occurs first as sound waves travel through the inner ear?
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What type of fluid fills the bony labyrinth of the inner ear?
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What primarily influences the fine-tuning responsiveness of inner hair cells?
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Which structure is responsible for detecting angular movements of the head?
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What type of neurons are present in the superior olive and contribute to sound processing?
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What change in the basilar membrane occurs along its length?
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What is the main auditory processing center in the brain?
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In the cochlea, what separates the scala media from the scala vestibuli?
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Which part of the ear is specifically involved in maintaining balance?
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What is the primary function of hair cells in the spiral organ of the cochlea?
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What is the endocochlear potential?
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What can cause the tympanic membrane to vibrate inefficiently?
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Which part of the ear is responsible for transmitting sound waves to the cochlea?
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How many rows of outer hair cells are present in the spiral organ of the cochlea?
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What is the primary function of the cochlear duct?
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Study Notes
Encoding Sound Intensity
- Firing rates of neurons increase with louder sounds
- Number of active neurons increases with louder sounds
- Loudness perceived is correlated with the number of active neurons
- Membrane potential of activated hair cells is more depolarized or hyperpolarized with louder sounds
Encoding Sound Frequency
- Tonotopic maps are present on the basilar membrane, spiral ganglion, and cochlear nucleus
- The basilar membrane resonates with increasingly lower frequencies from its base to apex
- Tonotopy is preserved in the auditory nerve and cochlear nucleus
- Bands of cells with similar characteristic frequencies increase from anterior to posterior in the cochlear nucleus
Phase Locking
- Action potentials are synchronized to specific parts of the frequency wave
- Low frequencies exhibit phase locking on every cycle or some fraction of cycles
- High frequencies are too fast/chaotic for reliable synchronization
- Thought to be important for sound localization and detailed sound processing
Mechanisms of Sound Localization
- Sound localization in the horizontal plane is achieved through interaural time delay and interaural intensity difference
- Interaural time delay is the difference in time for sound to reach each ear
- Interaural intensity difference is the difference in sound intensity at each ear due to the head's sound shadow
- The duplex theory of sound localization states:
- Low-frequency sounds (20–2000 Hz) are localized based on interaural time delay
- High-frequency sounds (2000–20,000 Hz) are localized based on interaural intensity difference
Mechanisms of Sound Localization: Coincidence Detection
- Impulses from the left and right cochlear nucleus reach the superior olive simultaneously
- This simultaneous arrival of impulses from both sides results in summation of signals and an action potential
Mechanisms of Sound Localization: Vertical Sound Localization
- Vertical sound localization is based on reflections from the pinna
Primary Auditory Cortex
- Tonotopy is present: cells with similar binaural interaction are organized in columns
- Unilateral lesions in the auditory cortex result in nearly normal auditory function
- This contrasts with lesions in the striate cortex, which cause complete blindness in one visual hemifield
- Different frequency bands are processed in parallel
- Auditory cortical neurons exhibit frequency tuning, meaning they have similar characteristic frequencies
- Isofrequency bands run mediolaterally across the A1 cortex
Beyond the Primary Auditory Cortex
- Auditory association areas interpret sounds, including pattern recognition and emotional association
Sense of Equilibrium (Vestibular System)
- Equilibrium is a response to head movements, relying on input from the inner ear, eyes, and stretch receptors
- The vestibular apparatus, located in the semicircular canals and vestibule, contains equilibrium receptors
- Vestibular receptors monitor static equilibrium
- Semicircular canal receptors monitor dynamic equilibrium
Dynamic Equilibrium Sensors (Crista Ampullares in Semicircular Canals)
- The crista ampullaris is the receptor for rotational acceleration
- It is a small elevation in the ampulla of each semicircular canal
- Cristae are excited by acceleration and deceleration of the head
- They are primarily stimulated by rotational (angular) movements, such as twirling
- Semicircular canals are located in all three planes of space (pitch, roll, yaw), enabling detection of all rotational movements of the head
Anatomy and Activation of Crista Ampullares
- Each crista contains supporting cells and hair cells that extend into a gel-like mass called the ampullary cupula
- Dendrites of vestibular nerve fibers encircle the base of hair cells
- Cristae respond to changes in the velocity of rotational movements of the head
- The inertia of the ampullary cupula causes the endolymph in the semicircular ducts to move in the direction opposite of the body's rotation, bending hair cells
Activation of Crista Ampullares: Bending of Hairs
- Bending hairs in the cristae causes depolarization, resulting in a faster rate of impulses reaching the brain
- Bending hairs in the opposite direction causes hyperpolarization, resulting in fewer impulses reaching the brain
- Rotational acceleration is a fast-adapting sense, meaning that after a few seconds, the static equilibrium sensors are responsible for providing equilibrium information
Push-Pull Activation of Semicircular Canals
- Three semicircular canals are present on each side of the head, enabling detection of all possible head rotation angles
- Each semicircular canal is paired on the opposite side of the head
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