FREQUENCY-RESPONSE AND OTHER PROPERTIES OF SINGLE FIBERS IN GUINEA-PIG COCHLEAR NERVE
FREQUENCY-RESPONSE AND OTHER PROPERTIES OF SINGLE FIBERS IN GUINEA-PIG COCHLEAR NERVE
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DOI：
10.1113/jphysiol.1972.sp009984
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发表时间：
1972-01-01
影响因子：
5.5
通讯作者：
EVANS, EF
中科院分区：
文献类型：
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作者：
EVANS, EF
1.取戊巴比妥钠和氨基甲酸乙酯麻醉豚鼠耳蜗神经的100多根单纤维作微电极记录。声学系统在鼓膜和阈值声级测量上进行了校准，并进行了修正。纤维的最小阈值接近文献报道的行为阈值的10-20分贝。例外的是来自制剂的纤维，这些材料有证据表明由于异常低血流灌注或局部损伤而导致耳蜗功能障碍，以及一些高频纤维。除去这些高阈值纤维，任何一种动物在给定频率下的阈值范围都不到20分贝。对于特征频率低于2 kHz的光纤，频率-阈值曲线(调谐曲线)的低频截止和高频截止的斜率分别为10-60和20-125分贝/倍频程，对于特征频率约为8 kHz的光纤，分别增加到90-180和200-600分贝/倍频程。这些斜率代表高频截止的最小值，在某些情况下，在高于阈值的较高水平上，高频截止增加到每八度1000分贝。在高于阈值30-50分贝时，低频截止突然变得不那么陡峭，接近于每八度5分贝。对于特征频率低于2 kHz的光纤，频率-阈值曲线的相对锐度范围为1-4，对于特征频率接近10 kHz的光纤，其相对锐度为3-15。大多数异常高阈值纤维的频率-阈值曲线的斜率和Q10分贝测量值接近或低于豚鼠基底膜振动模式的类似测量值。五分之四的耳蜗神经纤维自发放电频率大于1次/秒。除了近一半的高阈值纤维是静默的，没有观察到这种活动的速率和反应特性之间的一致关系。在这些和其他方面，对音调和滴答声刺激的反应特性类似于猫的耳蜗神经纤维。未观察到单音对自发放电的抑制作用。结论是，与早期报道相反，豚鼠的耳蜗神经纤维比现有的豚鼠基底膜位移的测量结果具有更强的频率选择性。就带宽而言，这种差异接近十倍。在最佳制备方法中发现了相当大范围的频带宽度，以及与病理性耳蜗纤维的机械功能近似的频率阈值曲线，这为基底膜移位模式后在耳蜗内发生的生理脆弱的锐化机制提供了间接证据。
1. Micro‐electrode recordings were obtained from over 100 single fibres in the cochlear nerve of the pentobarbitone or urethane anaesthetized guinea‐pig. The acoustic system was calibrated at the tympanic membrane and threshold sound level measurements so corrected.2. The minimum thresholds of the fibres approached with 10–20 dB of the behavioural thresholds reported in the literature. Exceptions to this were fibres from preparations where there was evidence of malfunction of the cochlea either from abnormally low perfusion or local damage, and a few high frequency fibres. With these high threshold fibres excepted, the range of thresholds at a given frequency in any one animal was less than 20 dB.3. The slopes of the low and high frequency cut‐offs of the frequency—threshold curves (‘tuning curves’) within 25 dB of minimum threshold, ranged from 10 to 60 and from 20 to 125 dB/octave respectively for fibres with characteristic frequencies below 2 kHz, increasing to 90–180 and 200–600 dB/octave respectively for fibres with characteristic frequencies at about 8 kHz. These slopes represent the minimum values for the high‐frequency cut‐offs, which increase towards 1000 dB per octave in some cases at higher levels above threshold. At 30–50 dB above threshold, the low frequency cut‐offs become suddenly less steep and approximate to 5 dB per octave.4. The relative sharpness of the frequency—threshold curves, measured as the ‘Q10 dB’, i.e. the ratio of characteristic frequency to the band width at 10 dB above minimum threshold, ranged from 1 to 4 for fibres with characteristic frequencies below 2 kHz, to 3–15 for fibres with characteristic frequencies near 10 kHz.5. The slopes and ‘Q10 dB’ measures of the frequency—threshold curves of most of the abnormally high threshold fibres approximated to, or were lower than those of analogous measurements of the guinea‐pig basilar membrane vibration patterns.6. Four fifths of the cochlear nerve fibres had spontaneous discharge rates greater than 1/sec. No consistent relationship was observed between the rate of this activity and response properties, with the exception that nearly half of the high threshold fibres were silent. In these and other respects the response properties to tonal and click stimuli resembled those of cochlear nerve fibres in the cat. In no case was inhibition of the spontaneous discharge by single tones observed.7. It is concluded that, contrary to earlier reports, the cochlear nerve fibres of the guinea‐pig are substantially more frequency selective than the existing measurements of the guinea‐pig basilar membrane displacement. In terms of band width, this discrepancy approaches a factor of ten. The finding of a considerable range of band widths within optimal preparations, and frequency—threshold curves approximating to the mechanical functions in fibres from pathological cochleas, provides circumstantial evidence for a physiologically vulnerable sharpening mechanism occurring within the cochlea subsequent to the displacement pattern of the basilar membrane.