Properties of motor units in the transversus abdominis muscle of the garter snake.
Properties of motor units in the transversus abdominis muscle of the garter snake.
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DOI：
10.1113/jphysiol.1987.sp016827
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发表时间：
1987-12
期刊：
影响因子：
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通讯作者：
J. Lichtman;R. S. Wilkinson
中科院分区：
文献类型：
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作者：
J. Lichtman;R. S. Wilkinson
1.研究了吊带蛇单纤维腹横肌运动单位的组织结构。这种小的节段性肌肉(60-100个纤维)包含三种不同的纤维类型(较快的抽动，F；较慢的抽动，S；和紧张性的，T)，它们主要以重复模式F，T，S，T，F，T等排列。2.运动单位图是通过激活单个运动轴突并识别由该轴突支配的所有肌肉纤维而获得的，使用活动诱导的细胞外标记分子的摄取来标记受刺激的轴突的突触前终末，或者使用系统的细胞内记录来识别由轴突激活的肌肉纤维。3.每条肌肉含有三种运动单位(F、T和S)，它们与三种类型的纤维相对应。运动单元中的所有肌肉纤维都是同一类型的。每个节段性肌肉包含大致相同数量的运动单位：一到两个较快的抽动，三到四个较慢的抽动和三个强直。4.各运动单位广泛分布于肌肉各处。运动单位内的纤维既不聚集也不反聚集。这表明，尽管轴突被限制为支配适当类型的纤维，但每个运动单位的分布并不产生纤维类型的交替模式。5.在几个实验中，对肌肉的一个节段性成分中的所有抽动运动单位进行了标测。任何一个轴突的投射都是随机的，不仅与肌肉的纤维类型有关，而且与其他轴突的神经供应有关。6.抽搐运动单元按大小等级排列。在每一块被检查的肌肉中，最大的运动单位是较快的抽动；一个较快的抽动运动轴突通常支配肌肉中所有较快的抽动纤维(14到24个纤维)。紧随其后的是三到四个较慢的抽搐运动单元，其大小从八到十个纤维到只有四到五个纤维的非常小的运动单元不等。7.每个紧张性运动神经轴突平均支配93个终板。与抽动运动单位相比，张力性运动单位的尺寸相对较大，这与张力性肌肉纤维将多神经元神经支配保留到成年的能力有关，这既是通过每个纤维提供5到7个终板位置，也是通过允许来自不同张力性运动轴突的末梢共同支配同一终板。
1. The organization of motor units in the single‐fibre‐thick transversus abdominis muscle of the garter snake has been studied. This small segmental muscle (60‐100 fibres) contains three distinct fibre types (faster twitch, F; slower twitch, S; and tonic, T) which are predominantly arranged in the repeating pattern F, T, S, T, F, T, etc. 2. Motor‐unit maps were obtained by activating an individual motor axon and identifying all of the muscle fibres innervated by that axon, using either the activity‐induced uptake of extracellular marker molecules to label presynaptic terminals of the stimulated axon, or systematic intracellular recording to identify muscle fibres activated by the axon. 3. Each muscle contained three types of motor units (F, T and S) that corresponded to the three types of fibres. All of the muscle fibres in a motor unit were of the same type. Each segmental muscle contained approximately the same number of motor units: one to two faster twitch, three to four slower twitch, and three tonic. 4. Each motor unit was dispersed widely throughout the muscle. Fibres within a motor unit were neither clustered nor anticlustered. This suggests that despite the fact that axons are constrained to innervate fibres of the appropriate type, the distribution of each motor unit does not generate the alternating pattern of fibre types. 5. In several experiments, all of the twitch motor units in one segmental component of the muscle were mapped. The projection of any one axon appeared random not only with respect to the muscle's fibre type pattern, but also with respect to the innervation supplied by other axons. 6. Twitch motor units were arranged according to a hierarchy of sizes. In each muscle examined, the largest motor unit was faster twitch; a single faster twitch motor axon usually innervated all of the faster twitch fibres in the muscle (fourteen to twenty‐four fibres). This was followed by three to four slower twitch motor units which varied in size from eight to ten fibres to very small motor units containing only four to five fibres. 7. Each tonic motor axon innervated an average of ninety‐three end‐plates per segmental muscle. The relatively large size of tonic motor units compared to twitch motor units is related to the ability of tonic muscle fibres to retain polyneuronal innervation into adulthood, both by providing five to seven end‐plate sites per fibre, and by allowing terminal boutons from different tonic motor axons to co‐innervate the same end‐plate.(ABSTRACT TRUNCATED AT 400 WORDS)