Myelinated

Figure 37. Diagram of an axon and its covering sheats

- surrounded by both myelinated sheath and lemmacytes
- have a smaller diameter of axons than unmyelinated one. The diameter corresponds to the thickness of the myelin sheath. If the 1st is larger, the 2nd is thicker
- the development of the myelin during histogenesis represent the multiple wrapping of lemmacyte’s plasma membrane around the axon
- in this case the nucleus and most of cytoplasm of lemmacytes become displaced on the outside
- electron micrograph shows the lamellar texture of the myelin. The myelin sheath doesn’t uniformly cover the axon
- the myelin is absent between adjacent lemmacytes
- such areas are known as Node of Ranvier
- internode distance varies in dimension from 0.08-1μm
- along internode under the LM, myelin shows cone-shaped cleft: cleft of Schmidt-Lantermann
- they are actually helical tunnel from the outside of the sheath to the inside. They appear as sparsely dispersed lamella separated by cytoplasm

The myelinated axons are surrounded by a lipid rich layer called the myelin sheath. The myelinated axons conduct impulses more rapidly than unmyelinated due to the presence of the nodes of Ranvier, where the axolemma is exposed to extracellular fluids via the intercellular space. The nerve impulse is jumped from node to node and it is called saltatory or discontinuous conduction.

Literature

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