Over time, myelinated fibers undergo structural changes. In a developing nervous system, the myelin sheath thickens and becomes more organized. In mature neurons, the myelin sheath is well-formed, with clearly defined nodes of Ranvier. However, in aging or pathological conditions, myelination can deteriorate. Histologically, this can be seen as thinner myelin sheaths, irregularities in myelin layering, and in severe cases, complete demyelination.
