Question

Myelin sheath is formed by
A)Ranvier cells
B)Muscle cells
C)Schwann cells
D)Axon

Answer 1

Myelin sheath is a layer rich in fat and it surrounds the axons of neurons. It acts as an insulating layer and also helps in increasing the rate of conduction of electrical signals. Also, the axon is covered by many myelinated areas each separated by gaps known as nodes of Ranvier.

Complete answer:
Following are the parts of a neuron :

Dendrites: These are branching structures which perform the function of receiving messages from other neurons and transmitting them to the cell body.

Cell body: It is composed of Golgi body, ER nucleus and mitochondria

Axon: Signals are transmitted from the cell body to axon which transmits them to other neurons.

Myelin is produced by glial cells known as oligodendrocytes in the central nervous system and by Schwann cells in the peripheral nervous system. It acts as an insulating layer which is rich in lipids. Hence option c) Myelin health is formed by Schwann cells is correct.

Based on the presence or absence of myelin sheath neurons are classified into myelinated and unmyelinated neurons.
In myelinated fibres Schwann cells wrap around the axon and in unmyelinated fibres, Schwann cells form grooves instead of wrapping around the axon.
Myelinated fibres appear white and have nodes and internodes whereas unmyelinated nerve fibres are grey and do not have nodes and internodes.
Speed of transfer of signals in myelinated fibres is faster than unmyelinated fibres. Nodes of Ranvier are also present in myelinated fibres and absent in unmyelinated fibres.

Hence, the correct answer is option (C)

Note: Myelin health is formed when oligodendrocytes or Schwann cells wrap around the axon. It is an insulating layer and also reduces the capacitance of the membrane of the axon. Myelin sheath is discontinuous and has nodes of Ranvier. Action potentials transmit from one node of Ranvier to the other and reach the terminal end. Myelin is white and also constitutes a white matter of CNS.