What are the Outer Hair Cells?
The outer hair cells (OHCs) are structures located within the cochlea of the inner ear. There are three rows of OHCs that sit on top of the basilar membrane and below the floating tectorial membrane. They act as basilar membrane motion detectors and are displaced by the tectorial membrane when the traveling wave of the basilar membrane occurs from incoming sound frequencies.
What are the functions of the Outer Hair Cells?
OHCs have many functions, but their primary role is the active mechanism. The active mechanism is a phenomenon where the OHCs amplify sound as the basilar membrane goes into motion. This active amplification occurs on the basilar membrane at the characteristic frequency of the incoming sound. For example, if the characteristic frequency of an incoming sound was 1000 Hz, the highest peak of the traveling wave would occur at 1000 Hz, due to the amplification of sound from the work of the OHCs. OHCs respond to vibration of the basilar membrane by stretching and contracting at a rate equal to the stimulating frequency.
How does Outer Hair Cell loss affect one's hearing?
The loss of OHCs is considered a sensorineural hearing loss and can greatly impact our hearing. OHC loss affects solely the inner ear because that is where the OHCs are located. As stated above, the active mechanism is crucial for amplifying sound at the characteristic frequency of the incoming sound source. Without the active mechanism, there would be less amplification of sound. This leads to a reduced and broader frequency selectivity of the sound source. A narrow and high peak response of the basilar membrane is critical in hearing because it amplifies the characteristic frequency of a sound, helping us distinguish between objects such as animals, musical instruments, and other things in our environment.
With this reduction in frequency selectivity, a person with OHC loss would have an increase in their hearing threshold (what we can just hear at the lowest level of sound) and they would also have a loss in sensitivity, particularly affecting their ability to hear quiet sounds, or to hear in a noisy environment. For example, one with OHC loss may have difficulty hearing their friend whisper into their ear, or hearing their friend talk while they walk through a busy city. OHC loss often leads to people using hearing aids, for they are designed to help amplify sound.
It is important to note, however, that without OHCs, the auditory nerve would still respond, but only to louder sounds because of the missing active mechanism. Also, although there is a loss of amplification of incoming sound without OHCs, people with OHC loss can still hear sound with using the temporal code.
The outer hair cells (OHCs) are structures located within the cochlea of the inner ear. There are three rows of OHCs that sit on top of the basilar membrane and below the floating tectorial membrane. They act as basilar membrane motion detectors and are displaced by the tectorial membrane when the traveling wave of the basilar membrane occurs from incoming sound frequencies.
What are the functions of the Outer Hair Cells?
OHCs have many functions, but their primary role is the active mechanism. The active mechanism is a phenomenon where the OHCs amplify sound as the basilar membrane goes into motion. This active amplification occurs on the basilar membrane at the characteristic frequency of the incoming sound. For example, if the characteristic frequency of an incoming sound was 1000 Hz, the highest peak of the traveling wave would occur at 1000 Hz, due to the amplification of sound from the work of the OHCs. OHCs respond to vibration of the basilar membrane by stretching and contracting at a rate equal to the stimulating frequency.
How does Outer Hair Cell loss affect one's hearing?
The loss of OHCs is considered a sensorineural hearing loss and can greatly impact our hearing. OHC loss affects solely the inner ear because that is where the OHCs are located. As stated above, the active mechanism is crucial for amplifying sound at the characteristic frequency of the incoming sound source. Without the active mechanism, there would be less amplification of sound. This leads to a reduced and broader frequency selectivity of the sound source. A narrow and high peak response of the basilar membrane is critical in hearing because it amplifies the characteristic frequency of a sound, helping us distinguish between objects such as animals, musical instruments, and other things in our environment.
With this reduction in frequency selectivity, a person with OHC loss would have an increase in their hearing threshold (what we can just hear at the lowest level of sound) and they would also have a loss in sensitivity, particularly affecting their ability to hear quiet sounds, or to hear in a noisy environment. For example, one with OHC loss may have difficulty hearing their friend whisper into their ear, or hearing their friend talk while they walk through a busy city. OHC loss often leads to people using hearing aids, for they are designed to help amplify sound.
It is important to note, however, that without OHCs, the auditory nerve would still respond, but only to louder sounds because of the missing active mechanism. Also, although there is a loss of amplification of incoming sound without OHCs, people with OHC loss can still hear sound with using the temporal code.
In summary, people without OHCs would:
Go to the "Speech and Music Perception" page to learn about how OHC loss affects these elements of hearing!
- have a broader frequency selectivity
- have difficulty hearing quiet sounds
- have difficulty distinguishing between vowels during speech
- have difficulty listening in noise
- still be able to hear otherwise, using predominantly the temporal code
Go to the "Speech and Music Perception" page to learn about how OHC loss affects these elements of hearing!