QUANTITATIVE STUDIES ON MATURATION OF CENTRAL AND PERIPHERAL PARTS OF INDIVIDUAL VENTRAL MOTONEURON AXONS .2. INTERNODAL LENGTH

  • 1 January 1978
    • journal article
    • research article
    • Vol. 127  (SEP) , 1-15
Abstract
The lengths of internodes on peripheral and central stretches of the same ventral motoneuron axons were measured in 6 day old rats. The former were more than twice as long as the latter. The distribution of peripheral internodal lengths was broader and was shifted to the right relative to that of central internodes. Short internodes were present centrally and peripherally throughout the early period of rapid myelination occurring immediately after birth. All such internodes appeared normal centrally, as did a proportion found peripherally. Some peripheral examples appeared to be degenerating. Some short internodes, both peripherally and centrally, increased in length to achieve a normal appearance. Many central stretches of ventral motoneuron axons which were myelinated at some levels possessed unmyelinated segments at other levels where they were covered by numerous short glial processes. Such bare stretches commonly occurred immediately deep to the cord surface. The lengths of the unmyelinated stretches decreased as age advanced, perhaps due to the extension of adjacent myelinated segments along them.