title: Stapes Vibration in the Chinchilla Middle Ear: Relation to Behavioral and Auditory-Nerve Thresholds.
abstract: The vibratory responses to tones of the stapes and incus were measured in the middle ears of deeply anesthetized chinchillas using a wide-band acoustic-stimulus system and a laser velocimeter coupled to a microscope. With the laser beam at an angle of about 40 ° relative to the axis of stapes piston-like motion, the sensitivity-vs.-frequency curves of vibrations at the head of the stapes and the incus lenticular process were very similar to each other but larger, in the range 15-30 kHz, than the vibrations of the incus just peripheral to the pedicle. With the laser beam aligned with the axis of piston-like stapes motion, vibrations of the incus just peripheral to its pedicle were very similar to the vibrations of the lenticular process or the stapes head measured at the 40 ° angle. Thus, the pedicle prevents transmission to the stapes of components of incus vibration not aligned with the axis of stapes piston-like motion. The mean magnitude curve of stapes velocities is fairly flat over a wide frequency range, with a mean value of about 0.19 mm(.)(s Pa(-1)), has a high-frequency cutoff of 25 kHz (measured at -3 dB re the mean value), and decreases with a slope of about -60 dB/octave at higher frequencies. According to our measurements, the chinchilla middle ear transmits acoustic signals into the cochlea at frequencies exceeding both the bandwidth of responses of auditory-nerve fibers and the upper cutoff of hearing. The phase lags of stapes velocity relative to ear-canal pressure increase approximately linearly, with slopes equivalent to pure delays of about 57-76 μs.
authors.affiliation: Instituto de Ciencias Biomédicas (Facultad de Medicina), Universidad de Chile, Santiago, Chile.
authors.forename: Luis
authors.initials: L
authors.lastname: Robles
authors.forename: Andrei N
authors.initials: AN
authors.lastname: Temchin
authors.forename: Yun-Hui
authors.initials: YH
authors.lastname: Fan
authors.forename: Mario A
authors.initials: MA
authors.lastname: Ruggero
mesh_terms: D000818:Animals; D001309:Auditory Threshold; D001522:Behavior, Animal; D002682:Chinchilla / Q000502:physiology*; D003056:Cochlear Nerve / Q000502:physiology; D007188:Incus / Q000502:physiology; D008297:Male; D013199:Stapes / Q000502:physiology*; D014732:Vibration