Chapter 16 - Section 16.4 - Study Guide - Assess Your Learning Outcomes - Page 625: 14

Outer hair cells (OHCs) play a critical role in tuning the cochlea to improve its sensitivity to differences in pitch, a process known as cochlear amplification or the cochlear amplifier. This mechanism enhances the cochlea's ability to discriminate between different frequencies and contributes to our ability to hear sounds with greater precision. Here's how OHCs achieve this tuning and amplification: 1. **Cochlear Amplification:** - OHCs have a unique property called electromotility. This means that when OHCs receive an electrical signal from the brain, they can change their length by contracting or elongating. - When sound vibrations travel through the cochlea, they create mechanical movements that cause the stereocilia on both inner and outer hair cells to bend. However, the mechanical sensitivity of OHCs is significantly greater than that of inner hair cells (IHCs). - This increased sensitivity allows OHCs to convert the weak mechanical vibrations of sound into electrical signals with high fidelity, enhancing the overall responsiveness of the cochlea to various frequencies. 2. **Cochlear Tuning:** - The cochlea is tonotopically organized, with different frequencies of sound vibrating specific regions of the basilar membrane. - OHCs play a role in fine-tuning this tonotopic organization. They act as an active mechanical filter that amplifies the vibrations of the basilar membrane in response to specific frequencies. - The OHCs' electromotility allows them to change their length in response to the incoming sound frequency. When a particular frequency of sound reaches the cochlea, the OHCs near that specific region of the basilar membrane elongate or contract. - This active process enhances the mechanical responsiveness of the basilar membrane at that frequency, essentially sharpening its tuning and improving the cochlea's ability to discriminate between slight differences in pitch. 3. **Otoacoustic Emissions (OAEs):** - OHCs' mechanical amplification can produce sound waves of their own, known as otoacoustic emissions (OAEs). These emissions are generated in response to the OHCs' active movements and can be measured using sensitive instruments. - OAEs are commonly used in clinical settings as a diagnostic tool to assess cochlear function and to detect hearing loss, particularly in newborns. In summary, outer hair cells (OHCs) are not just passive receptors of sound but actively contribute to cochlear amplification and tuning. By electromotility and their role in producing otoacoustic emissions, OHCs enhance the cochlea's sensitivity to differences in pitch and improve its ability to discriminate between different frequencies. This process is essential for our accurate perception of sounds and our ability to distinguish between various tones and pitches.

Outer hair cells (OHCs) play a critical role in tuning the cochlea to improve its sensitivity to differences in pitch, a process known as cochlear amplification or the cochlear amplifier. This mechanism enhances the cochlea's ability to discriminate between different frequencies and contributes to our ability to hear sounds with greater precision. Here's how OHCs achieve this tuning and amplification: 1. **Cochlear Amplification:** - OHCs have a unique property called electromotility. This means that when OHCs receive an electrical signal from the brain, they can change their length by contracting or elongating. - When sound vibrations travel through the cochlea, they create mechanical movements that cause the stereocilia on both inner and outer hair cells to bend. However, the mechanical sensitivity of OHCs is significantly greater than that of inner hair cells (IHCs). - This increased sensitivity allows OHCs to convert the weak mechanical vibrations of sound into electrical signals with high fidelity, enhancing the overall responsiveness of the cochlea to various frequencies. 2. **Cochlear Tuning:** - The cochlea is tonotopically organized, with different frequencies of sound vibrating specific regions of the basilar membrane. - OHCs play a role in fine-tuning this tonotopic organization. They act as an active mechanical filter that amplifies the vibrations of the basilar membrane in response to specific frequencies. - The OHCs' electromotility allows them to change their length in response to the incoming sound frequency. When a particular frequency of sound reaches the cochlea, the OHCs near that specific region of the basilar membrane elongate or contract. - This active process enhances the mechanical responsiveness of the basilar membrane at that frequency, essentially sharpening its tuning and improving the cochlea's ability to discriminate between slight differences in pitch. 3. **Otoacoustic Emissions (OAEs):** - OHCs' mechanical amplification can produce sound waves of their own, known as otoacoustic emissions (OAEs). These emissions are generated in response to the OHCs' active movements and can be measured using sensitive instruments. - OAEs are commonly used in clinical settings as a diagnostic tool to assess cochlear function and to detect hearing loss, particularly in newborns. In summary, outer hair cells (OHCs) are not just passive receptors of sound but actively contribute to cochlear amplification and tuning. By electromotility and their role in producing otoacoustic emissions, OHCs enhance the cochlea's sensitivity to differences in pitch and improve its ability to discriminate between different frequencies. This process is essential for our accurate perception of sounds and our ability to distinguish between various tones and pitches.