Outer hair cells respond better than inner hair cells to low-frequency sound

Evidence

Three rows of outer hair cells and one row of inner hair cells line the length of the cochlea. The outer hair cells are responsible for enhancing the vibration on the basilar membrane, particularly at low levels, sharpening the tuning of the vibration on the basilar membrane, and compressing the range of vibration represented by the basilar membrane. These hair cells lead to the mammalian ability to hear very low level sounds, and loss of these hair cells can cause a reduction in hearing sensitivity up to about 60 dB (Sellick et al., 1982). The inner hair cells transduce the vibratory signal into neural activity and synapse with the auditory nerve. Most afferent neurons (the neurons that send signals to higher auditory centers) synapse with the inner hair cells, and the tonotopic organization of the BM is maintained. Loss of either inner hair cells, their synaptic connections to the auditory nerve, or auditory nerve fibers has the potential to cause complete deafness. The amount of hearing loss and the frequencies affected will depend on the severity and location of the damage. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 228

The current biophysical experiments reveal a significant effect of LF sound exposure on the inner ear, and specifically on the function of OHCs. The observed effects are reflected in significant changes of quadratic distortion products, but importantly, in changes of SOAEs, which (for the ears that exhibit them) allows for a least-invasive evaluation of inner ear function. As the low-frequency stimuli used in this study are intense, mechanisms associated with acoustic overexposure and recovery thereof could in principle be responsible for the Bounce phenomenon. Temporary or permanent damage to OHCs represent an unlikely cause, as recovery from acoustic overexposure with sounds in the sensitive range of hearing is typically monotonic, does not oscillate and no hypersensitivity can be seen. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3744

Categorization

• DEFINE: Cleanly partitions the outer (mechanical amplifier) and inner (transducer) hair cell roles — the core functional division of the cochlea.
• corroborated: 4 independent passages support this claim — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 228; Dijk, Pim van, Physiology, Psychoacoustics and…, 3744
• XREF: connects to: Low-frequency sound’s after-effects arise from calcium homeostasis in outer hair cells — Dijk, Pim van, Physiology, Psychoacoustics and…, 3701; Low-frequency sound triggers larger cochlear responses than comparable higher frequencies. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3704; Perceptual insensitivity to low-frequency sound masks its physiological impact on the inner ear

Broader Connections

• Low-frequency sound’s after-effects arise from calcium homeostasis in outer hair cells #expands (0.85) — Dijk, Pim van, Physiology, Psychoacoustics and…, 3701
• Low-frequency sound triggers larger cochlear responses than comparable higher frequencies. #corroborates (0.80) — Dijk, Pim van, Physiology, Psychoacoustics and…, 3704
• Perceptual insensitivity to low-frequency sound masks its physiological impact on the inner ear #complicates (0.75)