Difference Between Myelinated and Unmyelinated Nerve Fibres

The key difference between myelinated and unmyelinated nerve fibres is that the myelinated nerve fibres have myelin sheaths around them while the unmyelinated nerve fibres do not have the sheath. Furthermore, the nerve impulse transmission is faster in myelinated nerve fibers while it is slower in unmyelinated nerve fibers.

A nerve cell has three components; namely cell body, dendrites, and axon. Nerve fibers are the slender processes of nerve cells. Axon is one of a nerve fiber. Axons carry nerve impulses (action potentials) away from the neuron cell body, and they are rapid in action. Moreover, compared to dendrites, axons are long. Mostly, one axon is present in one nerve cell. Myelin sheath is an insulating layer or covers formed around the axon to increase the speed of nerve impulse transmission. Schwann cells make the myelin sheath. However, axons can be myelinated or unmyelinated.

CONTENTS

1. Overview and Key Difference
2. What are Myelinated Nerve Fibres
3. What are Unmyelinated Nerve Fibres
4. Similarities Between Myelinated and Unmyelinated Nerve Fibres
5. Side by Side Comparison – Myelinated vs Unmyelinated Nerve Fibres in Tabular Form
6. Summary

What are Myelinated Nerve Fibres?

When an axon has a myelin sheath around it, we call it a myelinated axon or a myelinated nerve fiber. Since myelinated nerve fibers have an electrically insulating cover, their nerve impulse transmission is efficient and rapid.

Furthermore, they possess nodes of Ranvier. Because of these nodes of Ranvier, saltatory conduction of nerve impulse occurs and the speed of transmission increases. When a myelin sheath is present, the nerve fibers appear white in colour.

What are Unmyelinated Nerve Fibres?

Nerve fibers that do not have myelin sheaths around them are known as unmyelinated nerve fibers.

Since they do not cover with an electrically insulating layer, their impulse transmission is slow than myelinated nerve fibers.Unmyelinated nerve fibers are grey in colour.

What are the Similarities Between Myelinated and Unmyelinated Nerve Fibres?

• Both are present in the nervous system.
• They both transmit nerve impulses.

What is the Difference Between Myelinated and Unmyelinated Nerve Fibres?

Based on the presence and absence of a myelin sheath around a nerve fiber, there are two types of nerve fibers namely myelinated nerve fiber and unmyelinated nerve fiber respectively. As myelin sheath acts as an insulating cover for myelinated nerve fibers, they show quick transmission of nerve impulses while it is slower in unmyelinated nerve fibers. Furthermore, since myelin is a lipid, myelinated nerve fibers appear in white. But, unmyelinated nerve fibers appear in grey. The following infographic presents the difference between myelinated and unmyelinated nerve fibres in tabular form.

Summary – Myelinated vs Unmyelinated Nerve Fibres

A nerve cell has three components namely a cell body, dendrites and an axon. When the axon is myelinated, we call that neuron as a myelinated neuron. Axon is a slender process of a neuron which carries nerve impulses away from the nerve cell body. It is also known as a nerve fiber. When a nerve fiber has a myelin sheath around it, we call it a myelinated nerve fiber. On the other hand, when there is no myelin sheath around a nerve fiber, we call it unmyelinated nerve fiber. Myelin sheath forms an insulating cover. Hence, it increases the speed of impulse transmission. Therefore, myelinated nerve fibers transmit nerve impulses rapidly than unmyelinated nerve fibers. This is the difference between myelinated and unmyelinated nerve fibers.

Reference:

1.Morell, Pierre. “The Myelin Sheath.” Advances in Pediatrics., U.S. National Library of Medicine, 1 Jan. 1999. Available here 
2.Nature News, Nature Publishing Group. Available here  

Image Courtesy:

1.’Neuron with oligodendrocyte and myelin sheath’By Andrew c (talk) (Public Domain) via Commons Wikimedia  
2.’Saltatory Conduction’By Dr. Jana (CC BY 4.0) via Commons Wikimedia