A) neuroglial cells
B) Schwann cells
C) nerve cells
D) All of these
Correct Answer: B
Solution :
Myelin sheaths in the peripheral nervous system are formed by Schwann cells, which indent to receive an axon and then wrap themselves around it in a jelly roll fashion. Initially the wrapping is loose but the Schwann cell cytoplasm is gradually squeezed from between the membrane layers. When the wrapping process is complete many concentric layers of Schwann cell plasma membrane enclose the axon much-like gauze wrapped around an injured finger. This tight coil of wrapped membranes is the myelin sheath. Myelin protects and electrically insulates fibres from one another and it increases the speed of transmission of nerve impulses. The neurons (nerve cells) are the structural units of the nervous system. They are highly specialized cells that conduct messages in the form of nerve impulses from one part of the body to another. Neurons associated closely with much smaller cells called neuroglia or glial cells. Neuroglia in the central nervous system are astrocytes, microglia, ependymal cells and oligodendrocytes, while the neuroglia in peripheral nervous system are satellite cells and Schwann cells.
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