Ultrastructure Labeled (IMAGE) University of Wisconsin-Madison Caption In the mutant spinal cord, the oligodendrocyte, a cell that makes myelin, is surrounded by conductive fibers (called axons, marked with *) that lack myelin sheaths. On higher magnification, this cell has a huge increase in microtubules (arrows) that fill the cytoplasm and line up with cell membranes. Credit Benjamin August Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.