Final answer:
Myelinated nerve fibers include those in the CNS and peripheral nervous system, with oligodendrocytes in the CNS and Schwann cells in the peripheral system creating the myelin sheath. Myelin enhances signal speed and efficiency and appears as deep, dark layers in electron micrographs due to staining.
Step-by-step explanation:
The types of nerve fibers that are myelinated includes those associated with the central nervous system (CNS), where oligodendrocytes form the myelin sheath, and peripheral nerve fibers, where Schwann cells are responsible for myelination. Myelin sheath is composed of multiple layers of cell membrane and insulates axons to improve the speed and efficiency of electrical signal transmission. In electron micrographs, such as those from the University of Michigan WebScope, the myelin sheath is often visible due to the stain reacting with the compact layers of myelin, making them appear deep, dark, and black. This enables easier identification of myelinated versus unmyelinated nerve fibers.
Within the sympathetic system, myelinated fibers are called white rami communicantes. They are contrasted with gray rami communicantes, which are unmyelinated. Myelin itself consists of fat-containing cells, providing insulation properties, and is characteristically separated by unmyelinated gaps known as nodes of Ranvier. The myelination process vastly increases the speed at which nerve impulses are transmitted compared to unmyelinated axons, reduces energy consumption, and prevents 'cross talk' between adjacent nerves. These aspects underscore the importance of myelin for efficient functioning of the nervous system.