myelin sheath
The sheath of Schwann is also called the myelin sheath. It is a layer of fatty material that surrounds and insulates nerve fibers, allowing for faster transmission of nerve impulses.
The Schwann cell forms a myelin sheath around the axon of the nerve.
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Surrounding the myelin sheath, there is a thin membrane called neurilemmal sheath. This is also called neurilemma or sheath of Schwann. This contains Schwann cells, which have flattened and elongated nuclei. The cytoplasm is thin and modified to form the thin sheath of neurilemma enclosing the myelin sheath. One nucleus is present in each internode of the axon. The nucleus is situated between myelin sheath adn neurilemma. At the node of Ranvier (where myelin sheath is absent), the neurilemma invaginates and runs up to axolemma in the form of a finger like process. In nonmyelinated nerve fiber, the neurilemma continuously surrounds axolemma. Neurilemma is absent in central nervous system. Neurilemma is necessary for the formation of myelin sheath (myelinogeneis).
Its the Neurilemma.
Schwann cells form a myelin sheath around peripheral nerve fibers in the peripheral nervous system.
Myelin Sheath Cytoplasm Dendrites Cell Body
another name for the sheath of schwann is neurilemma.
Neurilemma
The cells that are thought to enable myelination to take place are called Glial Cells, which wrap themselves around the axions in a spiral fashion. This creates a sheath, or insulation, around the axion. It is often referred to as 'White Matter'.
The formation of myelin sheath around the axon is called the myelinogenesis. In the peripheral nerve, the myelinogenesis starts at 4th month of intrauterine life. It is completed only in the second year after birth. Before myelinogeneis, Schwann cells of the neurilemma are very close to axolemma as in the case of unmyelinated nerve fiber. The membrane of the schwann cell is double layered. The schwann cells wrap up and rotate around the axis cylinder in many concentric layers. The concentric layers fuse to produce the myelin sheath but the cytoplasm of the cells is not deposited. Outermost membrane of Schwann cell remains as neurilemma. Nucleus of these cells remains in between myelin sheath and neurilemma. In the central nervous system, the schwann cells are absent and the myelin sheath is formed by the neuroglial cells called the oligodendroglia.
The Schwann cells wrap themselves tightly around the axon like a jellyroll. During the wrapping process, the cytoplasm is squeezed from between adjacent layers of the Schwann cell membranes, so that when the process is completed a tight core of plasma membrane material encompasses the axon. This wrapping is the myelin sheath. The Schwann cell nucleus and the bulk of its cytoplasm end up just beneath the outermost portion of its plasma membrane. This peripheral part of the Schwann cell and its exposed plasma membrane is the neurilemma.