Chapter 11: Hearing Flashcards
What is the physical and perceptual definition of sound?
Physical: Sound is a pressure change in the air or other medium
Perceptual: sound is the experience we have of what we hear.
What is a sound wave and how are they described?
It a pattern of compression and refraction that travels through the air.
Sound waves can be described by frequency (the number of cycles per second, described as pitch) and amplitude (height of the sound wave, intensity of sound)
What is a complex tone? A periodic waveform?
Complex waves are made from combinations of pure tones. Each different component is called a harmonic.
Periodic waveform is the pattern of amplitude and frequency that repeat in a complex tone.
What is timbre?
Timbre is the quality that distinguishes 2 tones that have the same loudness, pitch, and duration but still sound the same. For example it is the difference between middle C on the panio and middle C on the guitar.
What are the main structures of the outer ear and their function?
Structures: Pinnae, auditory canal.
Functions: to protect the eardrum and facilitate resonance. The pinnae and ear canala reflect sound waves which interact with incoming sound waves to reinforce some over others. The sound wave most reinforced is called the resonant frequency and in humans this is the frequency associated with speech.
What are the main structures of the middle ear and their functions?
The Tympanic Membrane: Vibrates when the sound waves reach it.
Ossicles: Smallest bones called Malleus, Incus, and Stapes. they amplify the vibrations so that they can travel through the denser fluid of the inner ear. Ossicles have muscles attached to them that contract to dampen the vibrations of loud sounds (this is why our own voice or chewing is not deafening)
Oval Window: where vibrations move to the inner ear. Stapes transmits vibrations to the oval window
What are the main structures of the inner ear and their functions?
The cochlea: is divided into three main sections
- Scala Vestibuli (top canal)
- Scala Tympani (bottom Canal)
- Cochlear Partition (Middle canal, contains the basilar membrane and the organ of corti
The Basilar membrane vibrates in response to sound which causes movement in the organ of corti.
The organ of corti contains two types of hair cells which are the cite of transduction for the hearing system:
- inner hair cells (1 row)
- outer hair cells (3 rows)
The tectorial membrane extends over top of the hair cells.
How do Hair cells transduce sound into electrical signals
Hair cells bend in response to movement from the organ of corti. Because the hair cells are against the tectorial membrane, their tops (stereocilia) bend and pull open tiplinks which open up ion channels. When the hair cells bend back the tiplinks close stopping the flow of ions in the hair cells. The electrical signals triggered by the flow of ions travel from the hair cell to the auditory nerve fiber.
What is phase locking?
Auditory nerves fire in synchrony with the rise and fall of pressure from a pure tone.
How do nerve fibers signal frequency?
They signal frequency by which cells are firing, specific groups of hair cells respond to specific frequencies. Different locations on the basilar membrane vibrate stronger in response to different frequencies. Increased the hair cells that get vibrated the most will fire the most, indicating the frequency of the sound wave.
Describe the physical properties of the basilar membrane.
The base of the membrane is the end closest to the stapes. It is narrower and much stiffer than the apex. As such hair cells at the base respond to higher frequencies than hair cells at the apex.
What structure acts as the cochlear amplifier and how does it work?
The outer hair cells act as the cochlear apmplipher. Ion flow into the outer hair cells cause mechanical changes inside the cell that cause it to expand or retract which then pushes it at different pressures against the basilar membrane, affecting it’s sensitivity to specific frequencies.
What is the auditory pathway to the brain?
From the auditory nerve fibers –> Cochlear nucleus (separate for each ear) –> Superior olivary nucleus (bineural input) –> inferior colliculus of the midbrain –> medial geniculate nucleus of the thalamus –> auditory cortex in the temporal lobe
What are pitch neurons and where are they found?
Neurons that respond to specific ranges of pitch. In humans the neurons most responsive to pitch are in the anterior auditory cortex.
What are different types of hearing loss/deafness?
Prebycosis: hair cell damage resulting from the cumulative effects over time of noise exposure, or from the ingestion of hair cell damaging drugs, or from age related degeneration.
Noise Induced Hearing Loss: loud noises causing degeneration of hair cells (e.g. going to a concert)
Hidden Hearing Loss: Difficulty hearing in noisy environments. Caused by damage to auditory nerve fibers and is often undetected by standard hearing tests.
