组织学与胚胎学 内分泌系统 双语教学07Nerve Tissue.pptVIP

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * (2). Myelin sheath LM: sponge like (H E), Black (OsO4). The myelin is complex of lipids(80%) and proteins, lipids are dissolved out by lipid solvents. In EM it shows a series of concentrically arranged light and dark lamellae Incisure of myelin /Schmidt-Lanterman incisure : cone-shaped clefts (contain cytoplasm of the Schwann cell ). Incisure of myelin During the development of the myelin sheath, the schwann cell first fixes to the surface of the axon and axon penetrates into the groove of the schwann cell cytoplasm. The edges of the groove fuse together to form a . The mesaxon start to rotate around the axon, then form myelin lamella. Formation 轴突系膜 mesaxon 2. Myelinated nerve fibers in CNS Similar to Myelinated nerve fibers in PNS; No neurolemma, no incisures of myelin; Difference of myelinated nerve fiber in PNS and in CNS 1. The myelin-forming cells in peripheral nervous system are the Schwann cells, but in the central nervous system are oligodendrocytes. 2. In PNS, one Schwann cell forms one internodal segment, but in CNS one oligodendrocyte forms several internodal segments. 3. In PNS, each myelinated fiber is delimited by a basal lamina, and such fibers are separated from each other by connective tissue of the endoneurium. However, in the CNS, there is no basal lamina or endoneurium surrounding myelinated nerve fibers. 4. Mesaxons are present in peripheral myelinated nerve fibers, but not in the myelinated nerve fibers of the CNS. Myelin sheath is formed by processes of oligodendrocytes which can form several internode. 3. Unmyelinated nerve fibers (1) PNS Thin axons (single or group) indented into Schwann cells; No myelin sheath and nodes of Ranvier. (2) CNS Free axons among other myelinated nerve fibers and glial processes : Myelin sheath serving as an insulator, the nerve impulses jump from node to node