Lecture 11 - Hearing and Vestibular Systems

Question 1

What are sound waves?

Answer 1

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.

Question 2

How do sound waves travel through the air?

Answer 2

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.

Question 3

What is the speed at which sound waves travel in the air?

Answer 3

Sound waves travel away from their source at about 700 miles per hour.

Question 4

What role does the eardrum play in hearing?

Answer 4

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.

Question 5

What is transduction in the context of hearing?

Answer 5

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.

Question 6

What is the range of sound wavelengths that the human ear can transduce?

Answer 6

The human ear can transduce sound wavelengths ranging from 0.017 to 17 meters.

Question 7

At what frequency range can human hearing occur?

Answer 7

Human hearing occurs with vibrations between 20 and 20,000 times per second.

Question 8

How is loudness determined in sound waves?

Answer 8

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.

Question 9

What does pitch refer to in the context of sound?

Answer 9

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).

Question 10

How does timbre contribute to our perception of sound?

Answer 10

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.

Question 11

What characterizes noise in terms of sound waves?

Answer 11

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.

Question 12

If a musician plays a note on different instruments, how would timbre help you identify them?

Answer 12

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.

Question 13

What is the role of the outer ear?

Answer 13

The outer ear, including the pinna, funnels sound waves into the ear canal and causes the tympanic membrane (eardrum) to vibrate.

Question 14

What happens to sound as it travels through the ear canal?

Answer 14

Sound waves cause the tympanic membrane to vibrate, transmitting these vibrations to the middle ear.

Question 15

What are the three bones in the middle ear called?

Answer 15

The three small bones in the middle ear are called ossicles: the malleus, incus, and stapes.

Question 16

How do the ossicles function in hearing?

Answer 16

The vibrations from the tympanic membrane cause the ossicles to vibrate, which then transmits these vibrations to the oval window membrane.

Question 17

What is the cochlea, and what is its significance in hearing?

Answer 17

The cochlea is a fluid-filled, coiled structure in the inner ear that contains sensory neurons responsible for sound transduction.

Question 18

What occurs when the stapes pushes against the oval window?

Answer 18

The movement of the stapes against the oval window causes the membrane behind the round window to bulge outward.

Question 19

How does the basilar membrane respond to different sound frequencies?

Answer 19

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.

Question 20

Where on the basilar membrane are high-pitched and low-pitched sounds detected?

Answer 20

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.

Question 21

Describe the structure and function of the organ of Corti.

Answer 21

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.

Question 22

What are hair cells, and how do they function in hearing?

Answer 22

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.

Question 23

How do the cilia of outer and inner hair cells differ in their attachment?

Answer 23

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.

Question 24

Explain the mechanism of sound transduction in the cochlea.

Answer 24

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.

Question 25

If a person hears a very low bass note, which part of the basilar membrane is primarily activated?

Answer 25

The thick and wide end of the basilar membrane is primarily activated when a person hears a very low bass note.

Question 26

What are inner hair cells?

Answer 26

Inner hair cells are sensory cells in the cochlea that transmit auditory information to the brain and are essential for hearing.

Question 27

What are outer hair cells?

Answer 27

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.

Question 28

How do outer hair cells influence the sensitivity of inner hair cells?

Answer 28

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.

Question 29

How many outer hair cells are there compared to inner hair cells?

Answer 29

There are three times more outer hair cells than inner hair cells in the cochlea.

Question 30

What happens to individuals without functional inner hair cells?

Answer 30

Individuals without functional inner hair cells are completely deaf and cannot transmit auditory information to the brain.

Question 31

What is the impact of lacking functional outer hair cells?

Answer 31

Individuals lacking functional outer hair cells can hear but often experience poor hearing and may have difficulty detecting certain sounds.

Question 32

What are cilia in the context of hair cells?

Answer 32

Cilia are hair-like projections on hair cells that play a crucial role in detecting sound vibrations.

Question 33

What are tip links?

Answer 33

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.

Question 34

What is an insertional plaque?

Answer 34

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.

Question 35

How do loud noises affect hair cell cilia?

Answer 35

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.

Question 36

What happens to tip links after exposure to loud noises?

Answer 36

Tip links usually regenerate within a few hours after being broken, resulting in temporary hearing loss that typically resolves.

Question 37

How does the breakage of tip links serve as a protective mechanism?

Answer 37

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).

Question 38

What is place coding in auditory perception?

Answer 38

Place coding is the principle that different frequencies of sound stimulate hair cells at different locations on the basilar membrane, indicating the fundamental frequency (pitch) of the sound wave.

Question 39

How are moderate to high frequencies primarily encoded in the auditory system?

Answer 39

Moderate to high frequencies are primarily encoded through place coding, which is important for understanding human speech.

Question 40

What is rate coding (temporal coding) in the context of auditory perception?

Answer 40

Rate coding refers to the encoding of very low frequencies, where the frequency of action potentials in auditory neurons corresponds to the frequency of the sound wave.

Question 41

What is place coding in pitch perception?

Answer 41

Place coding refers to the mechanism where different frequencies of acoustic stimuli cause varying movements along the basilar membrane, with higher frequencies bending the membrane closer to the stapes, increasing hair cell activity in that area.

Question 42

How do higher frequency sounds affect the basilar membrane?

Answer 42

Higher frequency sounds cause the basilar membrane to bend closest to the stapes, resulting in increased activity of hair cells in that region.

Question 43

What is rate coding in the context of pitch perception?

Answer 43

Rate coding is a system for processing low frequency sounds, where the pattern of neurotransmitter release from hair cells furthest from the stapes determines the perception of these low frequencies.

Question 44

Why is rate coding important for low frequency pitch perception?

Answer 44

Rate coding is crucial for identifying the pitch of low frequency sounds because it relies on the specific patterns of activity from hair cells, which respond to different sound frequencies.

Question 45

How does anatomical coding of pitch function?

Answer 45

Anatomical coding of pitch works by having different frequency stimuli maximally deform distinct regions of the basilar membrane, which corresponds to the perception of pitch.

Question 46

What does the sensitivity of inner hair cells reveal about their response to sound?

Answer 46

The sensitivity of inner hair cells is represented by tuning curves, indicating that they respond to faint sounds only at specific frequencies and also to louder sounds across a range of frequencies.

Question 47

What happens to inner hair cells when outer hair cells are lesioned?

Answer 47

Lesions targeted at outer hair cells disrupt the responsiveness of inner hair cells to specific sounds, affecting pitch perception.

Question 48

How are moderate to high frequencies encoded in pitch perception?

Answer 48

Moderate to high frequencies are primarily encoded by place coding, which involves the location of hair cell activation on the basilar membrane.

Question 49

What determines loudness perception in sound?

Answer 49

Loudness is determined by the total number of active hair cells and their overall activity levels in response to a sound.

Question 50

How is timbre perceived in sound?

Answer 50

Timbre is perceived by assessing the specific mixture of hair cells activated throughout the cochlea, which provides information about the quality of the sound.

Question 51

What is the fundamental frequency of a sound wave?

Answer 51

The fundamental frequency is the lowest frequency present in a sound wave, which serves as the base frequency for the sound.

Question 52

How are overtones related to the fundamental frequency?

Answer 52

Overtones are higher frequencies that are generally integer multiples of the fundamental frequency, contributing to the overall quality of natural sounds.

Question 53

Imagine hearing a deep bass sound at a concert. How is the pitch of that sound likely perceived?

Answer 53

The pitch of the deep bass sound is likely perceived through rate coding, as it corresponds to lower frequency sounds processed by the hair cells furthest from the stapes.

Question 54

What is timbre?

Answer 54

Timbre refers to the specific mixture of frequencies (fundamental frequency plus overtones) emitted by different instruments when playing the same note, reflecting the complexity of the sound wave.

Question 55

What is the fundamental frequency?

Answer 55

The fundamental frequency is the lowest and most intense frequency of a complex sound, perceived as the basic pitch.

Question 56

What are overtones?

Answer 56

Overtones are frequencies at integer multiples of the fundamental frequency.

Question 57

How does timbre help identify musical instruments?

Answer 57

Timbre helps identify the instrument producing the sound by analyzing how the timbre changes over time.

Question 58

What mechanism do cochlear implants use to stimulate the cochlea?

Answer 58

Cochlear implants utilize the cochlea’s place coding system to stimulate different locations along the cochlea using 20 to 24 evenly spaced electrodes.

Question 59

How does loudness control work in cochlear implants?

Answer 59

The frequency of stimulation in cochlear implants regulates the perceived loudness of the sound.

Question 60

At what frequency range is speech best understood with cochlear implants?

Answer 60

Speech is best understood when stimulating frequencies between 250 Hz to 6500 Hz.

Question 61

What is the role of overtones in speech understanding?

Answer 61

The presence of overtones aids in perceiving the fundamental tone of human speech, which has a fundamental frequency of 100-250 Hz.

Question 62

What are interaural cues?

Answer 62

Interaural cues are differences in sound perception between the two ears that assist in localizing sounds.

Question 63

How does the brain determine sound direction using timing difference?

Answer 63

The brain analyzes which ear hears the sound first to determine the direction of the sound.

Question 64

How do high-frequency sounds assist in sound localization?

Answer 64

For sounds above 800 Hz, interaural loudness differences help locate the sound, as high-frequency sounds are dampened by the head.

Question 65

How are low-frequency sounds localized by the brain?

Answer 65

For sounds below 800 Hz, the brain uses phase differences between the ears to localize sound, effective only for wavelengths longer than the width of the head.

Question 66

What limitation do previous sound localization cues have?

Answer 66

Previous cues do not identify if a sound comes from the front, back, or above.

Question 67

How does timbre analysis assist in identifying the height of a sound?

Answer 67

The shape of the outer ear creates direction-selective filters that enhance or attenuate different frequencies depending on the sound's direction.

Question 68

Why is localization of sound height considered a learning process?

Answer 68

Localization of sound height requires learning through integrating visual and auditory perceptions, and changes in outer ear shape can affect this ability.

Question 69

What is the function of the organ of Corti in the auditory pathway?

Answer 69

The organ of Corti transmits auditory information to the brain via the cochlear nerve.

Question 70

In which part of the brain do signals first synapse after leaving the cochlear nerve?

Answer 70

Signals first synapse in the cochlear nuclei in the medulla, where they are analyzed in parallel paths.

Question 71

What is the role of the superior olivary nuclei?

Answer 71

The superior olivary nuclei are involved in sound localization.

Question 72

Where does auditory information go after the inferior colliculi?

Answer 72

Auditory information is relayed to the medial geniculate nucleus in the thalamus, which then sends it to the primary auditory cortex in the temporal lobe.

Question 73

What is tonotopic representation?

Answer 73

Tonotopic representation refers to the organization of the primary auditory cortex by frequency, where different areas respond best to specific sound frequencies.

Question 74

How is the primary auditory cortex organized?

Answer 74

The primary auditory cortex is organized by frequency, with different regions responding optimally to different sound frequencies.

Question 75

Where is the primary auditory cortex located?

Answer 75

The primary auditory cortex is located in the upper section of the temporal lobe, largely hidden in the lateral fissure.

Question 76

What are the belt and parabelt regions in the auditory cortex?

Answer 76

The belt and parabelt regions refer to the auditory association cortex that processes complex auditory information.

Question 77

What are the two processing streams of auditory information?

Answer 77

The two processing streams are the posterior (dorsal) auditory pathway, involved in sound localization, and the anterior auditory pathway, important for recognizing the source of sounds.

Question 78

How does the posterior auditory pathway function?

Answer 78

The posterior auditory pathway is involved in sound localization and integrates with the "where" vision pathway in the parietal lobe.

Question 79

What is the role of the anterior auditory pathway?

Answer 79

The anterior auditory pathway extends from the temporal lobe into the frontal lobe and is important for recognizing the source of sounds, functioning as an auditory object recognition pathway.

Question 80

What is auditory agnosia?

Answer 80

Auditory agnosia is a condition resulting from damage to the auditory association cortex, leading to difficulty in processing complex auditory forms like music and language.

Question 81

How do different areas of the auditory association cortex process complex auditory information?

Answer 81

Different areas of the auditory association cortex process elements such as melody, rhythm, harmony, and the perception of consonance (pleasant) versus dissonance (unpleasant), affecting emotional responses.

Question 82

What is amusia?

Answer 82

Amusia is the inability to perceive or produce melodic music, affecting the recognition and production of melodies

Question 83

How do individuals with amusia typically function in other auditory aspects?

Answer 83

Individuals with amusia can often converse, understand speech, recognize environmental sounds, and perceive emotions in music, but struggle to distinguish between consonant and dissonant music.

Question 84

What is the primary function of the vestibular system?

Answer 84

The vestibular system detects gravity and the tilts and turns of the head, contributing significantly to balance and maintaining an upright head position.

Question 85

What symptoms can arise from disruptions in the vestibular system?

Answer 85

Issues within the vestibular system can lead to symptoms such as dizziness and nausea.

Question 86

What are the otolith organs?

Answer 86

The otolith organs are structures in the vestibular system that comprise two distinct parts, the utricle and the saccule, which monitor head position and linear acceleration.

Question 87

What are the functions of the utricle and saccule?

Answer 87

The utricle monitors the angle of the head and linear acceleration, while the saccule also contributes to detecting head angle and linear acceleration.

Question 88

How do the otolith organs detect the position of the head?

Answer 88

The otolith organs detect the position of the head relative to gravity using the weight of small calcium carbonate stones (otoliths) to indicate head orientation and acceleration.

Question 89

What are the semicircular canals?

Answer 89

The semicircular canals are three ring-like, fluid-filled structures arranged in different planes that detect changes in head rotation (angular acceleration).

Question 90

Describe the mechanism by which the semicircular canals signal the brain about head movements.

Answer 90

When the head moves, fluid in the canals shifts, causing a gelatinous mass called the cupula to bend. This bending opens hair cells, which send signals to the brain regarding the head’s rotational movements.

Question 91

How do the otolith organs determine head movement in multiple directions?

Answer 91

One otolith is positioned in the horizontal plane, while the other is in the vertical plane, allowing the vestibular system to detect head movements in multiple directions.

Question 92

If a person quickly turns their head to the left, which vestibular structure primarily helps them sense this movement?

Answer 92

The semicircular canals primarily help sense the head's rotational movement when the head turns quickly, detecting angular acceleration.

Question 93

Consider someone on a roller coaster. How do the otolith organs and semicircular canals work together during sudden drops and turns?

Answer 93

During a sudden drop, the otolith organs detect changes in linear acceleration due to gravity, while the semicircular canals sense rapid changes in head rotation, allowing the brain to process the experience of motion and balance.

Question 94

How does the brain determine the horizontal and vertical location of a sound?

Answer 94

Horizontal localization (left vs. right): - Low-frequency sounds: Uses phase differences (time difference between ears). - High-frequency sounds: Uses loudness differences (volume difference between ears). Vertical localization (up vs. down): - Uses timbre (mixture of overtones/harmonics in the sound).