Leech hearts are hybrids; they are myogenic but need entrainment by a heartbeat central pattern generator (CPG) to execute functional patterns. Leech hearts are modular; two lateral segmented heart tubes running the length of the animal. Moving blood through the segmented heart tubes of leeches requires sequential constrictions, timed by a heartbeat CPG and relayed to each heart segment by likewise segmental motor neurons. The heartbeat CPG produces bilaterally asymmetric coordinations: rear-to-front peristaltic on one side and nearly synchronous on the other, periodically switching sides. We examined the neuromuscular transform (NMT) of isolated heart segments in response to electrical nerve-stimulation to identify the range of parameters (burst duration, intraburst pulse frequency, period) allowing the heart to constrict continuously and reliably. Constriction amplitudes increased with increasing intraburst frequencies and decreased with decreasing burst durations. Similar amplitudes were achieved with longer burst durations combined with lower frequencies or with shorter burst durations combined with higher frequencies. Long burst durations delayed relaxation, leading to summation and tetanus. The time, and its variability, between stimulus onset and time to constriction onset or to peak decreased with increasing frequency. Data previously obtained in vivo, showed that the HE motor neurons fired longer bursts at lower frequencies at long periods moving to shorter bursts with higher intraburst frequencies as the period shortened. In this scenario, active constriction started earlier, the time to reach full systole shortened allowing more time for relaxation. Relaxation time before the next motor neuron burst appears critical for maintaining constriction amplitude.

中文翻译：

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分割的心管的单个部分中的神经肌肉变换。

水蛭心是杂种；它们是生肌的，但需要由心跳中枢模式生成器 (CPG) 夹带来执行功能模式。水蛭心是模块化的；两个横向分段的心管，沿着动物的长度延伸。使血液通过水蛭的分段心管需要连续收缩，由心跳 CPG 计时，并通过同样的分段运动神经元传递到每个心脏节段。心跳 CPG 产生双边不对称协调：一侧是前后蠕动，另一侧几乎同步，周期性地切换两侧。我们检查了响应电神经刺激的孤立心脏节段的神经肌肉变换 (NMT)，以确定参数范围（突发持续时间、突发内脉冲频率、期间）允许心脏持续可靠地收缩。收缩幅度随着爆发内频率的增加而增加，并随着爆发持续时间的减少而减少。较长的突发持续时间与较低的频率相结合，或较短的突发持续时间与较高的频率相结合，可实现类似的振幅。长时间的爆发延迟了放松，导致总和和破伤风。刺激开始与收缩开始或达到峰值之间的时间及其可变性随着频率的增加而减少。先前在体内获得的数据表明，HE 运动神经元在长时间内以较低频率发射更长的爆发，随着时间的缩短，移动到具有较高内部爆发频率的较短爆发。在这种情况下，主动收缩更早开始，达到完全收缩的时间缩短，让您有更多时间放松。下一次运动神经元爆发之前的松弛时间对于维持收缩幅度至关重要。