大鼠听神经单纤维的活动

ACTIVITIES OF SINGLE COCHLEAR NERVE FIBERS IN RATS

本文以声压级(SP)的dB值为单位,用不同频率(从音频到超声)的声刺激,对大鼠听觉一级神经元325根单一纤维的活动进行了观察。结果表明:每一纤维都有自己的最佳频率和相应的最低阈值。测得最佳频率的最低值为0.58kHz,最高值为62.6kHz; 最低阈值为6dBSPL,其相应频率为27.49kHz;最敏感的频率范围在20—50kHz。频率-阈值曲线在比最佳频率高的一侧斜度陡峭,低的一侧倾斜缓慢。频率-阈值曲线的锐度若以Q值表示,它对最佳频率分布的回归曲线由最佳频率的低频向高频方向逐渐升高,且Q10,Q20,Q30,Q40,Q50,dB的回归曲线具有相似的倾斜度。绝大多数纤维都有自发放电。给最佳频率持续音作用时,随刺激强度的增强,放电速率增加,但到阈上30dB左右皆达饱和。由各频率的最低阈值绘成的听反应阈曲线与行为测听所得的听力曲线颇为近似。

Activities of 325 single cochlear nerve fibers in response to pure tones at variousfrequencies including ultrasonic sounds were observed in rats.The stimulus soundswere measured with a probe tube inserted into an ear canal and a microphone and.expressed in dB SPL.The best frequency(BF,characteristic frequency)and thethreshold at BF were determined in every fiber.The measured BF rangedfrom 0.58 kHz to 62.6 kHz.BF and the threshold at BF of a fiber with the lowestBF-threshold were 27.49kHz and 6dB SPL respectively.The highest sensitivitywas found in fibers with BF from 20 to 50 kHz. The tuning curve rose from BF and its slope was steeper for the high side thanthe low one as observed in other animals.The sharpness of the tuning curve was.expressed by Q_N values,where Q_N is the ratio of BF to the band width at N dB abovethe BF threshold.Mean and the variance of Q_(10dB),Q_(20dB),Q_(30dB),Q(40dB),Q_(50dB),all increased as the BF did. Almost all fibers had spontaneous discharge.The discharge rate increasedwith the increase in sound intensity and saturated at about 30 dB above the thresh-old.The auditory threshold curve obtained from distribution of the lowest BF-threshold of 325 fibers was consistent with the audiograms determined behaviorally.