Kennedy W R, Webster H F, Yoon K S
J Neurocytol. 1975 Dec;4(6):675-95. doi: 10.1007/BF01181630.
The primary sensory innervation of muscle spindles obtained by muscle biopsy of normal human volunteers was studied with the light and electron microscopes. The parent IA sensory fibre branched 4-6 times, became unmyelinated for 25-30 mum, then formed sensory terminals on each nuclear bag and chain intrafusal muscle fibre. The first 4--5 mum of the unmyelinated segment is believed to be an encoder zone because the plasmalemma was undercoated by a dense granular layer similar to that under other membranes where action potentials originate. A reconstruction from micrographs of serial longitudinal sections showed that the primary sensory ending on a nuclear bag fibre is an irregular coil with branches and varicose swellings. The terminals contain central aggregates of microfilaments often surrounded by mitochondria, small numbers of vesicles, cisterns and tubular profiles. The latter merge with the plasma membrane. Junctional complexes between the plasma membranes of the terminals and intrafusal muscle resemble fascia adherns and are postulated to act as attachment plaques. These could contribute to the transduction process by incresing the degree of distortion of the terminal's membrane when stretch is applied to the spindle. A mechanism is described which could account for some of the differences in sensitivity of the primary and secondary sensory endings.
通过对正常人类志愿者进行肌肉活检，利用光学显微镜和电子显微镜研究了肌梭的初级感觉神经支配。初级传入A类感觉纤维分支4 - 6次，在25 - 30微米的长度内变为无髓鞘，然后在每个核袋和核链肌梭内肌纤维上形成感觉终末。无髓鞘段的前4 - 5微米被认为是一个编码区，因为其质膜下有一层致密颗粒层，类似于动作电位起源的其他膜下的致密颗粒层。对连续纵向切片显微照片的重建显示，核袋纤维上的初级感觉末梢是一个带有分支和曲张肿胀的不规则线圈。终末含有微丝的中央聚集体，周围常有线粒体、少量囊泡、池和管状结构。后者与质膜融合。终末质膜与梭内肌之间的连接复合体类似于粘着小带，推测其作用为附着斑。当对肌梭施加牵张时，这些附着斑可通过增加终末膜的变形程度来促进转导过程。本文描述了一种机制，该机制可以解释初级和次级感觉末梢在敏感性上的一些差异。
