Desenvolvimento do sistema nervoso - Mielinização

Summary

In this video, Débora, a biomedical scientist and Ph.D. candidate in neuroscience, explains the crucial process of myelination in the nervous system. She covers the dynamic neurodevelopment process that occurs from prenatal to postnatal stages, highlighting the roles of oligodendrocytes and Schwann cells in forming myelin. The video also discusses the differences between central and peripheral myelination, the factors influencing whether axons are myelinated, and the consequences of demyelination, such as in autoimmune diseases like multiple sclerosis. It offers insights into the vital role of myelination in efficient neural communication and its implications in health.

Takeaways

• 😀 The process of myelination is crucial during the development of the nervous system, occurring both in prenatal and postnatal periods.
• 😀 Neurodevelopment extends over the first two decades of life, involving processes like neurogenesis, synaptogenesis, and the formation of glial cells.
• 😀 Myelination, the process of forming the myelin sheath around neurons, begins in the third trimester of pregnancy and continues throughout the first two decades of life.
• 😀 The myelin sheath is primarily made of lipids and serves as an insulating layer, helping action potentials travel efficiently down axons.
• 😀 Myelinated axons allow for rapid, saltatory conduction, where the action potential jumps between nodes of Ranvier, speeding up neural transmission.
• 😀 Unmyelinated axons have slower action potential propagation, but they are used for local communication within the same region of the nervous system.
• 😀 Oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system are responsible for myelination, but they differ in function.
• 😀 Oligodendrocytes can myelinate multiple axons, while Schwann cells myelinate only one axon at a time.
• 😀 The geometry of the axon, such as its curvature and diameter, influences whether myelination occurs, with straight, thicker axons being more likely to be myelinated.
• 😀 Issues with myelination can lead to demyelination, which is often associated with inflammatory diseases like multiple sclerosis or Guillain-Barré syndrome.

Q & A

What is myelination, and why is it important in neurodevelopment?

Myelination is the process of forming a protective sheath of myelin around the axons of neurons. This process is crucial for efficient and rapid signal transmission between neurons, which is essential for proper functioning of the nervous system. Myelination starts in the third trimester of pregnancy and continues through the first two decades of life, significantly impacting cognitive and motor development.

Which cells are responsible for myelination in the central and peripheral nervous systems?

In the central nervous system (CNS), oligodendrocytes are responsible for myelination, whereas in the peripheral nervous system (PNS), Schwann cells perform this function.

What role do oligodendrocytes and Schwann cells play in myelination?

Oligodendrocytes in the CNS can myelinate multiple axons simultaneously, while Schwann cells in the PNS myelinate individual axons. These cells wrap their cytoplasm around the axons to form the myelin sheath, which isolates the axons and increases the speed of nerve signal transmission.

How does myelination affect the conduction of action potentials?

Myelination allows for faster and more efficient conduction of action potentials along axons. The myelin sheath acts as an insulator, preventing ion exchange along the axon, which speeds up signal transmission. Additionally, the nodes of Ranvier, gaps in the myelin, enable the action potential to 'jump' from node to node, further enhancing speed.

What is the difference between myelinated and unmyelinated axons in terms of signal conduction?

Myelinated axons conduct action potentials faster due to the insulating properties of the myelin and the rapid 'jumping' of the action potential between nodes of Ranvier. In contrast, unmyelinated axons have slower conduction because the action potential must propagate along the entire length of the axon, resulting in a less efficient signal transmission.

What are the functional differences between the myelination in the central and peripheral nervous systems?

The primary difference lies in the type of cell involved in myelination. In the CNS, oligodendrocytes myelinate multiple axons, while Schwann cells in the PNS myelinate individual axons. Additionally, oligodendrocytes have their cell bodies farther from the axons they myelinate, whereas Schwann cells are located closer to the axons.

How does the structure of axons influence the myelination process?

The structure and size of axons influence the degree of myelination. Larger, more robust axons are typically myelinated more extensively, facilitating faster signal transmission over long distances. Smaller, thinner axons may either have less myelin or no myelin at all, and their function is typically localized to shorter communication distances within the nervous system.

What happens when myelination goes wrong or is disrupted?

When myelination is disrupted, it leads to a condition called demyelination, where the myelin sheath is damaged or degraded. This can result in slower signal transmission and can lead to various neurological impairments, including cognitive, motor, or sensory dysfunctions. Demyelination is often seen in autoimmune diseases like multiple sclerosis.

What are some diseases related to demyelination?

Some of the common diseases associated with demyelination include multiple sclerosis, Guillain-Barré syndrome, and chronic inflammatory demyelinating polyneuropathy. These diseases typically involve an immune system attack on myelinating cells, leading to damage or loss of the myelin sheath and subsequent neurological symptoms.

How can the body repair damaged myelin?

The body can repair damaged myelin through a process called remyelination, where other oligodendrocytes or Schwann cells take over the role of myelinating the affected axons. However, if the damage is too severe, axonal degeneration may occur, which can lead to permanent loss of function.