Rather, each myelin sheath insulates the axon over a single long section and, in general, each axon comprises multiple long myelinated sections separated from each other by short myelin sheath-gaps called nodes of Ranvier. ... In the CNS, axons carry electrical signals from one nerve cell body to another.
If a cell was to undergo all the activities, eg cell division my mitosis, it results in growth. When we were still zygotes, cell division happened by mitosis resulting in the grown ups we are now. Over division results in growth of cancer cells. And if the body exercises, Lymphocytes are produced more, resulting in more of them circulating in blood preventing disease attacks
It is a 25% chance of both of them being heads.