Eatock Ruth Anne, Hurley Karen M, Vollrath Melissa A
The Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Tex 77005, USA.
Audiol Neurootol. 2002 Jan-Feb;7(1):31-5. doi: 10.1159/000046860.
Mammalian vestibular afferents respond robustly to head movements at low frequencies and provide input to reflexes that control eye, head and body position. Vestibular organs have distinctive regions and hair cells: Type II cells receive bouton afferent endings and type I cells receive large calyx afferent endings. In the rodent utricle, type II cells are broadly tuned to frequencies between 10 and 30 Hz. Other recent data suggest that otolith organs function in this frequency range, which is higher than previously imagined. Some of the tuning derives from adaptation of the transducer current, which is best fitted with a double exponential decay with time constants of approximately 4 and 40 ms. Further tuning is provided by basolateral conductances, principally outwardly rectifying, voltage-gated K+ conductances. The kinetics of the K+ currents tend to vary with location in the sensory epithelium and therefore may contribute to regional variation in afferent physiology. Type I hair cells have a large, negatively activating K+ conductance, g(K,L), that confers a very low input resistance and therefore attenuates the receptor potential. This may reduce nonlinearity in the receptor potential, a possibly useful feature for the motor reflexes served by the vestibular system. On the other hand, the small receptor potentials together with unusually negative resting potentials are hard to reconcile with calcium-mediated quantal transmission. This problem may be overcome by factors that inhibit g(K,L)'s activation at resting potential. Also, the calyx may support nonquantal transmission.
哺乳动物的前庭传入神经对低频头部运动有强烈反应，并为控制眼睛、头部和身体位置的反射提供输入。前庭器官有不同的区域和毛细胞：II型细胞接受纽扣状传入末梢，I型细胞接受大花萼状传入末梢。在啮齿动物的椭圆囊中，II型细胞对10至30赫兹之间的频率有广泛的调谐。最近的其他数据表明，耳石器官在这个频率范围内起作用，这比之前想象的要高。一些调谐来自换能器电流的适应性，它最适合用时间常数约为4和40毫秒的双指数衰减来拟合。进一步的调谐由基底外侧电导提供，主要是外向整流的电压门控钾电导。钾电流的动力学往往随感觉上皮中的位置而变化，因此可能导致传入生理学的区域差异。I型毛细胞有一个大的、负向激活的钾电导g(K,L)，它赋予非常低的输入电阻，因此减弱受体电位。这可能会减少受体电位中的非线性，这对前庭系统服务的运动反射可能是一个有用的特征。另一方面，小的受体电位加上异常负的静息电位很难与钙介导的量子传递相协调。这个问题可能通过在静息电位下抑制g(K,L)激活的因素来克服。此外，花萼可能支持非量子传递。
