Stokes D R, Josephson R K
Department of Biology, Emory University, Atlanta, GA 30322, USA.
J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2004 Apr;190(4):279-90. doi: 10.1007/s00359-003-0490-3. Epub 2004 Jan 24.
Sound production in cicadas is powered by a pair of large muscles whose contractions cause buckling of cuticular tymbals and thereby create sound pulses. Sound is modulated by control muscles that alter the stiffness of the tymbals or change the shape of the abdominal resonance chamber. Muscle ultrastructure and contractile properties were characterized for the tymbal muscle and two control muscles, the ventral longitudinal muscle and the tymbal tensor, of the periodical cicada Magicicada septendecim. The tymbal muscle is a fast muscle that is innervated by a single motoraxon. The control muscles are an order of magnitude less massive than the tymbal muscles, but their innervation patterns were considerably more complex. The tensor muscle is innervated by two axons, each of which evokes rather slow twitches, and the ventral muscle is innervated by at least six axons, some of which produce fast and the others slow contractions. Muscle contraction kinetics correlated well with ultrastructure. Fibers of the tymbal muscle and the portions of the ventral muscle thought to be fast were richly supplied with transverse tubules (T-tubules) and sarcoplasmic reticulum (SR); slow portions of the ventral muscle and the tensor muscle had relatively little SR.
蝉的发声是由一对大型肌肉驱动的，这些肌肉的收缩会导致表皮鼓膜弯曲，从而产生声脉冲。声音通过控制肌肉进行调节，这些控制肌肉会改变鼓膜的硬度或改变腹部共鸣腔的形状。对周期蝉七叶蝉的鼓膜肌以及两块控制肌肉（腹侧纵肌和鼓膜张肌）的肌肉超微结构和收缩特性进行了表征。鼓膜肌是一种快速肌肉，由单一运动轴突支配。控制肌肉的质量比鼓膜肌小一个数量级，但其神经支配模式要复杂得多。张肌由两条轴突支配，每条轴突引发的抽搐相当缓慢，而腹侧肌由至少六条轴突支配，其中一些产生快速收缩，另一些产生缓慢收缩。肌肉收缩动力学与超微结构密切相关。鼓膜肌的纤维以及腹侧肌中被认为是快速收缩部分的纤维富含横管（T管）和肌浆网（SR）；腹侧肌和张肌的缓慢收缩部分的肌浆网相对较少。
