Takahashi-Iwanaga H
Department of Anatomy, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
Ital J Anat Embryol. 2001;106(2 Suppl 1):481-7.
The fine structure of sensory nerve endings and their topographical relationships with surrounding tissues were examined by a combination of scanning and transmission electron microscopy in order to analyze the mechanism of mechanoreception. Observations were reported on Ruffini endings in periodontal ligaments of rat incisors, and on longitudinal lanceolate endings surrounding rat sinus hairs. Both types of receptors exhibited the triplet structure known as the axon-Schwann cell complex; a flattened axon terminal was sandwiched between two Schwann cell lamellae. The two receptor types additionally revealed their specific modifications at each distal end, where fine tuft-like processes of Schwann cells projected into surrounding tissues with finger-like projections of an axon terminal attached to their bases. In the Ruffini endings of the periodontal ligament, the terminal tufts coiled about collagen bundles in favor of continuous transmission of tissue distortions to their accompanying axon fingers. In the lanceolate endings of sinus hair follicles, the Schwann cell tufts were suspended in an amorphous matrix with only their end feet anchored to rigid connective tissue elements. Terminal axon fingers associated with these Schwann cell processes were supposed to transiently deflect during acceleration and deceleration phases of a given hair movement because of inertia. The present study proposes the terminal tuft of Schwann cell processes and their accompanying axon fingers as a structural complex which potentially contributes to mechano-electric transduction.
为了分析机械感受机制，运用扫描电子显微镜和透射电子显微镜相结合的方法，研究了感觉神经末梢的精细结构及其与周围组织的拓扑关系。报告了对大鼠切牙牙周膜中鲁菲尼小体以及大鼠鼻窦毛周围纵向梭形末梢的观察结果。两种类型的感受器均呈现出被称为轴突 - 施万细胞复合体的三联体结构；扁平的轴突终末夹在两个施万细胞板层之间。此外，两种感受器在各自的远端还显示出特定的修饰，施万细胞的细簇状突起向周围组织突出，轴突终末的指状突起附着在其基部。在牙周膜的鲁菲尼小体中，终末簇围绕胶原束盘绕，有利于将组织变形持续传递给其伴随的轴突指状结构。在鼻窦毛囊的梭形末梢中，施万细胞簇悬浮在无定形基质中，只有其终足锚定在坚硬的结缔组织成分上。与这些施万细胞突起相关的终末轴突指状结构由于惯性，在给定毛发运动的加速和减速阶段可能会短暂偏转。本研究提出施万细胞突起的终末簇及其伴随的轴突指状结构是一种潜在有助于机械 - 电转换的结构复合体。
