Zoran M J, Drewes C D, Fourtner C R, Siegel A J
Department of Zoology, Iowa State University, Ames 50010.
J Comp Neurol. 1988 Sep 1;275(1):76-86. doi: 10.1002/cne.902750107.
Neuroanatomical and ultrastructural studies of the paired lateral giant nerve fibers (LGFs) in posterior segments of the tubificid worm, Branchiura sowerbyi, demonstrate that the fibers are 1) segmental in origin (two cell bodies per segment), 2) joined longitudinally and transversely to form an intersegmental syncytial network, and 3) surrounded by a myelinlike sheath. The LGFs are unique among paired giant fiber systems because of their extreme asymmetry, the diameter of the left fiber being several times greater than that of the right. Electrophysiological studies demonstrate that the small, right fiber has a high input resistance and, during mechanosensory stimulation, functions as the locus for LGF spike initiation. The larger, left fiber contributes by enhancing the speed of LGF spike conduction along the animal. One physiological benefit of this asymmetric arrangement may be optimization of escape reflex sensitivity to mechanosensory inputs.
对颤蚓（Branchiura sowerbyi）后段成对的外侧巨神经纤维（LGFs）进行的神经解剖学和超微结构研究表明，这些纤维具有以下特点：1）起源于节段性（每节有两个细胞体）；2）纵向和横向连接形成节间合胞体网络；3）被类髓鞘包裹。LGFs在成对的巨纤维系统中是独特的，因为它们极度不对称，左侧纤维的直径比右侧大几倍。电生理研究表明，较小的右侧纤维具有高输入电阻，在机械感觉刺激期间，它作为LGF动作电位起始的位点发挥作用。较大的左侧纤维则通过提高LGF动作电位沿动物体传导的速度来发挥作用。这种不对称排列的一个生理益处可能是优化逃逸反射对机械感觉输入的敏感性。
