Macefield Vaughan G, Knellwolf Thomas P
School of Medicine, Western Sydney University , Sydney , Australia.
Neuroscience Research Institute , Sydney , Australia.
J Neurophysiol. 2018 Aug 1;120(2):452-467. doi: 10.1152/jn.00071.2018. Epub 2018 Apr 18.
Muscle spindles are ubiquitous encapsulated mechanoreceptors found in most mammalian muscles. There are two types of endings, primary and secondary, and both are sensitive to changes in muscle length and velocity, with the primary endings having a greater dynamic sensitivity. Unlike other mechanoreceptors in the somatosensory system, muscle spindles are unique in possessing motor innervation, via γ-motoneurons (fusimotor neurons), that control their sensitivity to stretch. Much of what we know about human muscles spindles comes from studying the behavior of their afferents via intraneural microelectrodes (microneurography) inserted into accessible peripheral nerves. We review the functional properties of human muscle spindles, comparing and contrasting with what we know about the functions of muscle spindles studied in experimental animals. As in the cat, many human muscle spindles possess a background discharge that is related to the degree of muscle stretch, but mean firing rates are much lower (~10 Hz). They can faithfully encode changes in muscle fascicle length in passive conditions, but higher level extraction of information is required by the central nervous system to measure changes in muscle length during muscle contraction. Moreover, although there is some evidence supporting independent control of human muscle spindles via fusimotor neurons, any effects are modest compared with the clearly independent control of fusimotor neurons observed in the cat.
肌梭是大多数哺乳动物肌肉中普遍存在的被囊化机械感受器。存在两种类型的末梢，即初级末梢和次级末梢，二者都对肌肉长度和速度的变化敏感，其中初级末梢具有更高的动态敏感性。与躯体感觉系统中的其他机械感受器不同，肌梭的独特之处在于其通过γ运动神经元（梭内运动神经元）接受运动神经支配，这些神经元控制着肌梭对拉伸的敏感性。我们对人类肌梭的许多了解都来自于通过插入可触及外周神经的神经内微电极（微神经ography）研究其传入纤维的行为。我们回顾了人类肌梭的功能特性，并将其与我们对实验动物中研究的肌梭功能的了解进行比较和对比。与猫一样，许多人类肌梭具有与肌肉拉伸程度相关的背景放电，但平均放电频率要低得多（约10赫兹）。它们能够在被动条件下忠实地编码肌肉束长度的变化，但中枢神经系统需要更高层次的信息提取来测量肌肉收缩期间的肌肉长度变化。此外，尽管有一些证据支持通过梭内运动神经元对人类肌梭进行独立控制，但与在猫中观察到的梭内运动神经元的明显独立控制相比，任何影响都较小。
