Question

Myelin sheath covers
A) Muscle fibre
B) Nerve fibre
C) Collagen fibre
D) Tendon

Answer 1

Hint: Myelin sheath is a lipid or fatty substance produced by schwann cells. It provides insulation and increases the rate of transmission of impulse along the axon. It is important for signal transduction.

Complete answer:
To answer this question, we will look at the structure of each of these cells.
A) Muscle cell-Muscle cells are called sarcomeres, they are long cylindrical structures bound by the plasma membrane (sarcolemma). The cytoplasm is called sarcoplasm which contains the sarcoplasmic reticulum. Sarcomere consists of actin and myosin filaments which help in the contraction and relaxation of muscles.
B) Nerve cell- A nerve cell consists of a cell body, an axon and dendrites. An impulse travels from the cell body to the axon and is transmitted to another nerve cell. In some nerve cells, Schwann cells secrete a lipid layer called myelin sheath which covers the axon of the nerve cell. It acts as an insulator and helps in the transmission of the impulse.
C) Collagen fibre- Collagen fibres are made up of collagen, a fibrous protein. They have high tensile strength. Along with elastic and reticulate fibres, they form connective tissues.
D) Tendons- Tendon is a type of dense connective tissue, composed of collagen fibres. It joins the muscle to bone.

We can conclude that the myelin sheath covers the axon of the nerve cell. Hence, the correct answer is option B.

Note: A nerve cell is also called a neuron. The axon of neurons of the Peripheral Nervous System (PNS) is covered by a myelin sheath, which is formed by the Schwann cells. Axons that have the myelin sheath are called myelinated axons while the axons which do not have the myelin sheath are called non-myelinated neurons