Question

The bundles of nerve fibres are called
A. Fasciculi
B. Epineurium
C. Perineurium
D. Neurilemma

Answer 1

Hint: The nervous system in the animals are composed of two important parts which are the central nervous system and peripheral nervous system. The CNS or the central nervous system contain groups of long slender projections which are known as axons while the PNS or peripheral nervous system consists of nerves.

Complete answer:
The nervous system is the system that conducts the signals and impulses to different parts of the body. It is made up of special types of cells or the nerve cells. THe nerve cells are also known as neurons. The neurons consist of long and thin projections. The projections are known as the axons.
The nerves fibres are arranged in the form of bundles. These bundles are known as fasciculi. The fasciculi are in turn made up of several smaller bundles of nerve fibres. Each nerve cell is covered in its external position known as the epineurium. The epineurium is a dense sheath of connective tissues. It is a layer made up of flat cells. It is then followed by another layer which is known as the perineurium.
The perineurium forms a covering like structure around the bundles of nerve fibres or the fascicles. The inner membrane that covers the fascicles is known as the endoneurium. It consists of an internal layer of material which is known as the glycocalyx. It also consists of an outer delicate mesh like structures of the collagen fibres. Inside the endoneurium, the individual neurons are covered by a protein known as endoneurial fluid.
Neurilemma is the outermost cytoplasmic layer of nucleated cells known as the Schwann cells. The Schwann cells are also known as the neurolemmocytes and it surrounds the axon of the neuron. The neurilemma forms the outermost layer of the nerve fibres present in the peripheral nervous system. It is also known as the neurolemma or the sheath of Schwann.

Therefore, the correct option is option A.

Note: The arrangement of the nerve fibres in a bundle like fashion is known as fasciculi. The fascicules are formed by much smaller bundles of nerve fibres. It is surrounded by the perineurium. The perineurium is the innermost layer of cells and is followed by the epineurium which is present to the external.