Lecture 11 - Hearing and Vestibular Systems Flashcards
What are sound waves?
Sound waves are fluctuations in air pressure generated by vibrating objects, causing surrounding air molecules to alternately condense and rarefy, which allows the sound to travel.
How do sound waves travel through the air?
Sound waves travel through the air by causing air molecules to alternately come closer together and pull apart, creating regions of high and low pressure.
What is the speed at which sound waves travel in the air?
Sound waves travel away from their source at about 700 miles per hour.
What role does the eardrum play in hearing?
The eardrum moves in and out in response to changes in air pressure caused by sound waves, allowing the conversion of sound waves into neural signals.
What is transduction in the context of hearing?
Transduction is the process by which the human ear converts fluctuations in air pressure from sound waves into neural signals that the brain can interpret.
What is the range of sound wavelengths that the human ear can transduce?
The human ear can transduce sound wavelengths ranging from 0.017 to 17 meters.
At what frequency range can human hearing occur?
Human hearing occurs with vibrations between 20 and 20,000 times per second.
How is loudness determined in sound waves?
Loudness in sound waves is determined by the wave’s amplitude, which is the size of the air pressure changes between compressed (high-pressure) and rarified (low-pressure) areas. The bigger this difference, the louder the sound we hear.
What does pitch refer to in the context of sound?
Pitch is how high or low a sound is, and it depends on how fast the sound wave vibrates, measured in hertz (Hz), which tells you how many cycles occur per second.
A high pitch (like a whistle) occurs when the sound wave has a high frequency, meaning it vibrates many times per second (for example, 1000 Hz means 1000 cycles per second).
A low pitch (like a drumbeat) occurs when the sound wave has a low frequency, meaning it vibrates fewer times per second (for example, 50 Hz means 50 cycles per second).
How does timbre contribute to our perception of sound?
Timbre is the unique quality or “voice” of a sound that allows us to distinguish between different sources, even if they have the same pitch and loudness. It arises from the complexity of the sound wave, including its overtones and frequencies. For example, timbre lets us tell the difference between a guitar and a piano playing the same note.
What characterizes noise in terms of sound waves?
Noise is sound that doesn’t follow a regular pattern or rhythm, meaning the air pressure variations are random and irregular. Unlike music or tones, which have repeating patterns that can be recognized as specific pitches or notes, noise lacks this structure, making it harder to identify or categorize.
If a musician plays a note on different instruments, how would timbre help you identify them?
Timbre helps you identify the source of the sound by allowing you to distinguish the unique quality and complexity of each instrument’s sound wave.
What is the role of the outer ear?
The outer ear, including the pinna, funnels sound waves into the ear canal and causes the tympanic membrane (eardrum) to vibrate.
What happens to sound as it travels through the ear canal?
Sound waves cause the tympanic membrane to vibrate, transmitting these vibrations to the middle ear.
What are the three bones in the middle ear called?
The three small bones in the middle ear are called ossicles: the malleus, incus, and stapes.
How do the ossicles function in hearing?
The vibrations from the tympanic membrane cause the ossicles to vibrate, which then transmits these vibrations to the oval window membrane.
What is the cochlea, and what is its significance in hearing?
The cochlea is a fluid-filled, coiled structure in the inner ear that contains sensory neurons responsible for sound transduction.
What occurs when the stapes pushes against the oval window?
The movement of the stapes against the oval window causes the membrane behind the round window to bulge outward.
How does the basilar membrane respond to different sound frequencies?
The basilar membrane is a structure in the cochlea of the inner ear that helps detect sound vibrations. It moves in response to sound frequencies: high and medium frequencies cause different parts of the basilar membrane to move, while low frequencies make the tip of the membrane move in sync with the sound vibrations. This movement allows the brain to interpret different sound pitches.
Where on the basilar membrane are high-pitched and low-pitched sounds detected?
High-pitched sounds are detected at the thick and narrow end of the basilar membrane (closest to the oval window), while low-pitched sounds are detected at the thin and wide end.
Describe the structure and function of the organ of Corti.
The organ of Corti is the receptive organ within the cochlea, consisting of the basilar membrane at the bottom, the tectorial membrane at the top, and auditory hair cells in the middle.
What are hair cells, and how do they function in hearing?
Hair cells are the sensory cells responsible for sound transduction, with cilia that move in response to sound vibrations, leading to the opening of ion channels and changes in their membrane potential.
How do the cilia of outer and inner hair cells differ in their attachment?
The cilia (hair-like structures) of outer hair cells are directly connected to the stiff tectorial membrane in the cochlea, so they move as this membrane moves in response to sound vibrations. In contrast, the cilia of inner hair cells are not attached to the tectorial membrane and instead move freely in the fluid around them, responding to pressure changes caused by vibrations. This difference allows outer hair cells to amplify sound signals, while inner hair cells focus on transmitting these signals to the brain.
Explain the mechanism of sound transduction in the cochlea.
Sound waves cause the basilar membrane to move relative to the tectorial membrane, resulting in the bending of hair cell cilia, which opens ion channels and alters the membrane potential of the hair cells.
If a person hears a very low bass note, which part of the basilar membrane is primarily activated?
The thick and wide end of the basilar membrane is primarily activated when a person hears a very low bass note.
What are inner hair cells?
Inner hair cells are sensory cells in the cochlea that transmit auditory information to the brain and are essential for hearing.
What are outer hair cells?
Outer hair cells are sensory cells in the cochlea that act like tiny motors to adjust hearing sensitivity. When they detect sound, they contract and expand in response to vibrations, amplifying these vibrations in the tectorial membrane above them. This amplification increases sensitivity to faint sounds and improves our ability to distinguish between different pitches and volumes, making them crucial for fine-tuning sound perception.
How do outer hair cells influence the sensitivity of inner hair cells?
Outer hair cells adjust the flexibility of the tectorial membrane by contracting or elongating in response to sound. This alters the membrane’s interaction with the inner hair cells’ stereocilia, enhancing or reducing the sensitivity of inner hair cells to specific sound frequencies. By fine-tuning this interaction, outer hair cells help improve the detection of different frequencies, ensuring that the auditory system responds with greater accuracy across a range of sounds.
How many outer hair cells are there compared to inner hair cells?
There are three times more outer hair cells than inner hair cells in the cochlea.
What happens to individuals without functional inner hair cells?
Individuals without functional inner hair cells are completely deaf and cannot transmit auditory information to the brain.
What is the impact of lacking functional outer hair cells?
Individuals lacking functional outer hair cells can hear but often experience poor hearing and may have difficulty detecting certain sounds.
What are cilia in the context of hair cells?
Cilia are hair-like projections on hair cells that play a crucial role in detecting sound vibrations.
What are tip links?
Tip links are tiny, stretchy fibers connecting the tips of adjacent cilia on hair cells, helping them coordinate movement to detect sound vibrations more effectively.
What is an insertional plaque?
An insertional plaque is the spot where a tip link, a tiny filament, connects two cilia (hair-like structures). This plaque contains an ion channel that opens or closes based on tension in the tip link, allowing ions to enter as sound vibrations move the cilia.
How do loud noises affect hair cell cilia?
Loud noises can break the tip links connecting the cilia, leading to temporary hearing loss since hair cells cannot transmit auditory information without these links.
What happens to tip links after exposure to loud noises?
Tip links usually regenerate within a few hours after being broken, resulting in temporary hearing loss that typically resolves.
How does the breakage of tip links serve as a protective mechanism?
Breakage of tip links may prevent excessive glutamate release onto the cochlear nerve, which can cause permanent cell death through excitotoxicity (excessive stimulation of neurons by excitatory neurotransmitters).
