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When a peripheral fiber is severed, the myelin sheath provides a track along which regrowth can occur. However, the myelin layer does not ensure a perfect regeneration of the nerve fiber. Some regenerated nerve fibers do not find the correct muscle fibers, and some damaged motor neurons of the peripheral nervous system die without regrowth.
Myelin is formed by oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.Therefore, the first stage of myelinogenesis is often defined as the differentiation of oligodendrocyte progenitor cells (OPCs) or Schwann cell progenitors into their mature counterparts, [4] followed by myelin formation around axons.
Sensory fiber types Type Erlanger-Gasser Classification Diameter Myelin Conduction velocity Associated sensory receptors; Ia: Aα: 13–20 μm: Yes: 80–120 m/s [5] Muscle spindle fibres Ib Aα: 13–20 μm: Yes: 80–120 m/s: Golgi tendon organ: II: Aβ: 6–12 μm: Yes: 33–75 m/s: All cutaneous mechanoreceptors including pacinian ...
The myelin sheath insulates the nerve fiber from the extracellular fluid and speeds up signal conduction along the nerve fiber. [34] In the peripheral nervous system, Schwann cells are responsible for myelin production. These cells envelop nerve fibers of the PNS by winding repeatedly around them. This process creates a myelin sheath, which not ...
The insulation must be proportional to the diameter of the fibre inside. The optimal ratio of axon diameter divided by the total fiber diameter (which includes the myelin) is 0.6. [24] Oligodendrocytes in rat cerebellum stained with antibody to myelin basic protein in red and for DNA in blue. Two oligodendrocyte cell bodies are clearly visible ...
Structure of a typical neuron with Schwann cells in the peripheral nervous system. Neurons are highly specialized for the processing and transmission of cellular signals. Given the diversity of functions performed in different parts of the nervous system, there is a wide variety in their shape, size, and electrochemical properties.
Lamellar microtubules: They are the microtubules that eventually wrap around the axon, forming the myelin sheath. Actin-based: These include terminal foot processes of podocytes and dendritic spines (small protrusions arising from dendrites). [3] IF-based: The predominant cytoskeletal element within astrocyte processes at birth is microtubules.
Spontaneous myelin repair was first observed in cat models. [49] It was later discovered to occur in the human CNS as well, specifically in cases of multiple sclerosis (MS). [50] Spontaneous myelin repair does not result in morphologically normal oligodendrocytes and is associated with thinner myelin compared to axonal diameter than normal ...