What is the Difference Between Schwann Cell and Myelin Sheath

The main difference between Schwann cell and myelin sheath is that Schwann cells wrap around the axon of the neuron to form the myelin sheath while myelin sheath serves as an electrically insulating layer.  

Schwann cell and myelin sheath are two types of structures in the axon of the neuron. Furthermore, Schwann cells produce myelin while myelin sheath increases the speed of signal transmission.

Key Areas Covered 

1. What is Schwann Cell
     – Definition, Features, Role
2. What is Myelin Sheath
     – Definition, Features, Role
3. What are the Similarities Between Schwann Cell and Myelin Sheath
     – Outline of Common Features
4. What is the Difference Between Schwann Cell and Myelin Sheath
     – Comparison of Key Differences

Key Terms 

Myelin, Myelin Sheath, Node of Ranvier, Saltatory Conduction, Schwann Cell, Transmission of Nerve Impulses

What is Schwann Cell 

A Schwann cell is a type of principal glial cell in the peripheral nervous system (PNS), supporting the PNS.  Furthermore, Schwann cells were named after the physiologist, Theodor Schwann. There are two main types of Schwann cells in the PNS as myelinating Schwann cells and non-myelinating Schwann cells. However, only myelinated Schwann cells produce myelin.  

Figure 1: Schwann Cells

In addition to the formation of the myelin sheath, Schwann cells play a major role in the regeneration of nerves. Schwann cells aid in the destruction of axons via phagocytosis in response to the damages of neurons. This forms a tunnel which guides the regeneration. Also, Schwann cells are important to keep the nerve cells alive. 

What is Myelin Sheath 

Myelin sheath is a layer found on the myelinated nerve fibers. It consists of Schwann cells. Typically, a Schwann cell covers 100 μm of an axon. Thus, 10,000 Schwann cells cover up 1 m length of an axon. There is a gap between two Schwann cell units called the node of Ranvier. Moreover, the myelinating Schwann cells produce myelin, a fatty, white substance that serves as an electrical insulator.  

Figure 2: Myelin Sheath

Furthermore, the peripheral nervous system of vertebrates relies on the insulation of axons by a myelin sheath to speed up the transmission of nerve impulses. Here, the myelin sheath decreases the capacitance of the axon and the action potential transmits jumping from one node to the other. Hence, this process is known as saltatory conduction. It can increase the conduction velocity by 10 times. 

Similarities Between Schwann Cell and Myelin Sheath 

• Schwann cell and myelin sheath are two types of structures found on the axon of the neurons. 
• Both of them occur on the neurons of the peripheral nervous system. 
• In addition, their main function is to speed up the transmission of nerve impulses by electrically insulating the axon. 

Difference Between Schwann Cell and Myelin Sheath 

Definition 

Schwann cell refers to a glial cell that wraps around the nerve fiber in the peripheral nervous system, and forms the myelin sheaths of peripheral axons while myelin sheath refers to the insulating covering that surrounds an axon with multiple spiral layers of myelin, that is discontinuous at the nodes of Ranvier, and that increases the speed at which a nerve impulse can travel along an axon. These definitions explain the basic difference between Schwann cell and myelin sheath.

Significance 

Schwann cell is a cell that wraps around the axon of the neuron while myelin sheath consists of myelinating Schwann cells. 

Function 

Their function is also a major difference between Schwann cell and myelin sheath. Schwann cells secrete myelin while myelin sheath serves as an electrical insulator, speeding up the signal transmission through neurons. 

Conclusion 

Schwann cell wraps around the axon of the neurons, providing support. In addition, it produces myelin, which is an electrical insulator. Schwann cells form the myelin sheath, which is involved in the saltatory conduction where the speed of the signal transmission increases. Therefore, the main difference between Schwann cell and myelin sheath is their structure and function.

Reference:

1. “Schwann cell myelination” Cold Spring Harbor perspectives in biology vol. 7,8 a020529. doi:10.1101/cshperspect.a020529. Available Here

Image Courtesy:

1. “Neuron” (CC BY-SA 3.0) via Commons Wikimedia  
2. “Neuron with oligodendrocyte and myelin sheath” By Neuron_with_oligodendrocyte_and_myelin_sheath.svg: *Complete_neuron_cell_diagram_en.svg: LadyofHatsderivative work: Andrew c (talk) – Neuron_with_oligodendrocyte_and_myelin_sheath.svg (Public Domain) via Commons Wikimedia