RT Journal Article SR Electronic T1 Identified motoneurons and their innervation of axial muscles in the zebrafish JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 2267 OP 2277 DO 10.1523/JNEUROSCI.06-08-02267.1986 VO 6 IS 8 A1 M Westerfield A1 JV McMurray A1 JS Eisen YR 1986 UL http://www.jneurosci.org/content/6/8/2267.abstract AB The organization of spinal cord motoneurons and their innervation of axial (white) muscles in the zebrafish were studied. Motoneurons can be divided into 2 classes, primary and secondary, on the basis of their cell-body sizes and positions. Each side of each spinal segment contains 3 primary motoneurons that are uniquely identifiable as individuals by their stereotyped cell-body positions and peripheral branching patterns. Moreover, these motoneurons precisely innervate cell-specific subsets of contiguous muscle fibers in mutually exclusive regions of their own body segment. Individual muscle fibers receive inputs from a single primary motoneuron and, in addition, from up to 3 secondary motoneurons. The results demonstrate that the precision of innervation previously described in invertebrates is also present in some vertebrates.