Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 12 - Section 12.3 - Study Guide - Assess Your Learning Outcomes - Page 471: 2

Answer

The myelin sheath is a lipid-rich, insulating structure that wraps around and covers the axons of many neurons in both the central nervous system (CNS) and the peripheral nervous system (PNS). The myelin sheath is crucial for the efficient and rapid conduction of nerve impulses. The structure of the myelin sheath and how it is produced by glial cells in the CNS and PNS are as follows: **Structure of the Myelin Sheath:** The myelin sheath consists of multiple layers of specialized cell membranes that wrap around the axon. The key components and structure of the myelin sheath include: 1. **Lipid Bilayers:** The myelin sheath is primarily composed of lipid bilayers, which are layers of phospholipid membranes. These lipid bilayers are rich in lipids such as cholesterol and glycolipids. 2. **Proteins:** Although the myelin sheath is predominantly lipid-based, it also contains some proteins. These proteins are involved in maintaining the structure and function of the myelin sheath and axon. 3. **Nodes of Ranvier:** In between the myelin sheath, there are regularly spaced gaps called Nodes of Ranvier. These nodes play a critical role in the propagation of nerve impulses by allowing the action potential to "jump" from node to node, which speeds up signal conduction. **Production of the Myelin Sheath:** The myelin sheath is produced by different types of glial cells in the CNS and PNS: **In the Central Nervous System (CNS):** - Oligodendrocytes are responsible for producing the myelin sheath in the CNS. Each oligodendrocyte can extend multiple processes, each of which can wrap around and insulate different axons. However, unlike Schwann cells in the PNS, oligodendrocytes do not wrap around the entire axon but provide myelin segments at intervals along the axon. Multiple oligodendrocytes work together to myelinate a single axon. **In the Peripheral Nervous System (PNS):** - Schwann cells, also known as neurolemmocytes, are responsible for producing the myelin sheath in the PNS. Each Schwann cell wraps itself around a single axon and spirally produces multiple layers of myelin sheath around it. Schwann cells play a crucial role in insulating and protecting PNS axons and promoting rapid signal transmission. They also participate in axon regeneration after injury. The process of myelination involves the growth and extension of the glial cell processes around the axon, followed by the deposition of multiple layers of lipid-rich membranes, forming the myelin sheath. Myelination is vital for increasing the speed of action potential conduction and maintaining the health and function of axons in the nervous system.

Work Step by Step

The myelin sheath is a lipid-rich, insulating structure that wraps around and covers the axons of many neurons in both the central nervous system (CNS) and the peripheral nervous system (PNS). The myelin sheath is crucial for the efficient and rapid conduction of nerve impulses. The structure of the myelin sheath and how it is produced by glial cells in the CNS and PNS are as follows: **Structure of the Myelin Sheath:** The myelin sheath consists of multiple layers of specialized cell membranes that wrap around the axon. The key components and structure of the myelin sheath include: 1. **Lipid Bilayers:** The myelin sheath is primarily composed of lipid bilayers, which are layers of phospholipid membranes. These lipid bilayers are rich in lipids such as cholesterol and glycolipids. 2. **Proteins:** Although the myelin sheath is predominantly lipid-based, it also contains some proteins. These proteins are involved in maintaining the structure and function of the myelin sheath and axon. 3. **Nodes of Ranvier:** In between the myelin sheath, there are regularly spaced gaps called Nodes of Ranvier. These nodes play a critical role in the propagation of nerve impulses by allowing the action potential to "jump" from node to node, which speeds up signal conduction. **Production of the Myelin Sheath:** The myelin sheath is produced by different types of glial cells in the CNS and PNS: **In the Central Nervous System (CNS):** - Oligodendrocytes are responsible for producing the myelin sheath in the CNS. Each oligodendrocyte can extend multiple processes, each of which can wrap around and insulate different axons. However, unlike Schwann cells in the PNS, oligodendrocytes do not wrap around the entire axon but provide myelin segments at intervals along the axon. Multiple oligodendrocytes work together to myelinate a single axon. **In the Peripheral Nervous System (PNS):** - Schwann cells, also known as neurolemmocytes, are responsible for producing the myelin sheath in the PNS. Each Schwann cell wraps itself around a single axon and spirally produces multiple layers of myelin sheath around it. Schwann cells play a crucial role in insulating and protecting PNS axons and promoting rapid signal transmission. They also participate in axon regeneration after injury. The process of myelination involves the growth and extension of the glial cell processes around the axon, followed by the deposition of multiple layers of lipid-rich membranes, forming the myelin sheath. Myelination is vital for increasing the speed of action potential conduction and maintaining the health and function of axons in the nervous system.
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