Hoyle G
J Exp Biol. 1978 Apr;73:173-203. doi: 10.1242/jeb.73.1.173.
The jumping muscle of orthopterous insects contains fibres that possess an intrinsic rhythm (IR) of slow contraction. The contributing fibres are generally synchronized, but as many as three or four pacemakers are present. The frequency, amplitude and duration of IR contractions fluctuate erratically over a 24 h period. Metathoracic DUM neurone bursts suppress IR for a few minutes. Other, unidentified dorsal neurones enhance its amplitude. In addition to IR, the extensor tibiae shows intrinsic basic tonus (BT). BT is relaxed for several s by low-frequency burst output from unidentified metathoracic dorsal neurones. DUM neurone bursts may enhance extensor BT, relax it, or leave it unaffected. The effects on IR of various regimes of activity in the slow extensor tibiae (SETi) and the common inhibitor (CI) axons were examined. CI affects IR when stimulated at frequencies above 2 Hz. It causes amplitude depression and reduced duration of individual IR contractions as well as increased frequency. At 30 Hz and above, CI completely suppresses IR. An enhanced IR contraction starts within a few milliseconds of the termination of a CI train. At low frequencies (below 10 Hz) SETi causes increased frequency and decreased amplitude of IR, with a depressed IR contraction following cessation of the SETi burst. At frequencies above 15 Hz the SETi-evoked contraction dominates tension development, though IR summates with it during the rising phase. In quiescent preparations not showing IR, SETi stimulation at 10 Hz often started up IR. Single SETi or FETi impulses can initiate an IR contraction, and cause altered phasing, with up to a quintupling of frequency. After a critical period has elapsed following the onset of an IR contraction, a single single impulse in any one of the three axons will terminate it abruptly. The early termination is followed by a reduced interval which is proportional to the reduced IR contraction time. The rhythm of accumulated readiness to go into an IR contraction is independent of the pacemaker rhythm that initiates the contraction.
直翅目昆虫的跳跃肌含有具有缓慢收缩固有节律（IR）的纤维。起作用的纤维通常是同步的，但存在多达三或四个起搏器。IR收缩的频率、幅度和持续时间在24小时内不规则波动。后胸DUM神经元爆发会抑制IR几分钟。其他未识别的背侧神经元会增强其幅度。除了IR，胫节伸肌还表现出固有基础张力（BT）。未识别的后胸背侧神经元的低频爆发输出会使BT松弛几秒钟。DUM神经元爆发可能增强、松弛或不影响伸肌BT。研究了慢胫节伸肌（SETi）和共同抑制（CI）轴突的各种活动模式对IR的影响。当以高于2Hz的频率刺激时，CI会影响IR。它会导致单个IR收缩的幅度降低、持续时间缩短以及频率增加。在30Hz及以上时，CI会完全抑制IR。在CI序列终止后的几毫秒内会开始增强的IR收缩。在低频（低于10Hz）时，SETi会导致IR频率增加、幅度降低，在SETi爆发停止后会出现抑制的IR收缩。在高于15Hz的频率时，SETi诱发的收缩主导张力发展，尽管在上升阶段IR会与之叠加。在不显示IR的静止标本中，以10Hz刺激SETi通常会启动IR。单个SETi或FETi冲动可以启动IR收缩，并导致相位改变，频率增加高达五倍。在IR收缩开始后的关键时期过后，三个轴突中任何一个的单个冲动都会突然终止它。早期终止之后是间隔缩短，这与IR收缩时间缩短成正比。积累的准备进入IR收缩的节律与启动收缩的起搏器节律无关。
