Question

Which has the highest speed of nerve impulse?
A. Medullated nerve
B. Non-medullated nerve
C. Cranial nerve
D. Spinal nerve

Answer 1

Hint: Nerve fibres can be myelinated as well as non-myelinated that depends on the presence of myelin sheath. The presence or absence of myelin sheath in nerve fibres determines the speed of impulse generation and transmission.

Complete answer: The basic working unit of the brain, which is specialized and is designed to transmit some information to the other cells. These cells are divided into three parts- cell body, an axon, and dendrites. Nodes of ranvier are microscopic gaps found between myelinated axons. They help to speed up the propagation of action potentials along the axon via saltatory conduction. They are periodic gaps present on the axons of the neurons and are insulated by the myelin sheath and it helps in the rapid conduction of nerve impulses. In the peripheral nervous system, schwann cells synthesize myelin sheaths around the neuronal axons. The myelin sheath consists of myelin. The myelin sheath is made up of water-soluble ions and lipids. They are a type of glial cells that help in keeping myelinated and unmyelinated nerve fibres alive. The sheath made by schwann cells is not continuous. They are derived from neural crest cells. They help in maintaining and regeneration of axons of the neurons. Various neurotrophic factors help in the regulation of schwann cells. When the nerve fibres do not have myelin sheath they are known as non-myelinated or non-medullated fibres and the one with myelin sheath is known as myelinated/medullated fibers. The medullated neurons are present in the white matter of the brain and spinal cord as well as spinal and cranial nerves. Non-medullated neurons are found in the autonomous nervous system. Myelinated neurons have a high speed of nerve impulse as compared to non-myelinated neurons.
Hence, the correct option is (A)-Medullated nerve.

Note: In vertebrates, the action potential travels along the myelin-coated axons which are regenerated at the nodes of ranvier that lack myelination and are identified by the tight junctions between the axons and the glial cells. Specific proteins are enriched in this region of the nodes.