Neural Glial Cells and Myelin Sheath

Neural Glial Cells and Myelin Sheath

Overview

• Neural glial cells, or neuroglia, are support cells in the nervous system.

• Six types of neuroglia play various roles in homeostasis and the well-being of nervous tissue.

• The myelin sheath and its relationship to glial cells will also be discussed.

Supporting Cells of the Nervous System

• There are six types of supporting cells in the nervous system, divided into those found in the central nervous system (CNS) and the peripheral nervous system (PNS).

• Four cell types are in the CNS and two in the PNS.

• These cells provide different functions crucial for the health and operation of the nervous system.

Gray Matter vs. White Matter

• The brain and spinal cord consist of gray matter and white matter.

• Gray matter contains a higher concentration of neuronal cell bodies, giving it a darker coloration.

• White matter contains axons, many of which are covered in myelin, a white fatty substance.

• Myelin gives the white matter its color.

Central Nervous System Neuroglia

Astrocytes

• Astrocytes are the largest and most abundant neuroglial cell type in the CNS.

• They have a star-shaped appearance.

• Functions:

  • Maintain and regulate ion concentration in the interstitial fluid.

  • Play a minor role in the blood-brain barrier, which is mainly regulated by endothelial cells lining capillaries without intercellular clefts and limited vesicular transport.

  • Support neurons by storing and supplying nutrients like glycogen (a polysaccharide form of glucose).

  • Act as a nutrient reserve for neurons, which are highly metabolically active.

  • Fill spaces in the nervous tissue with scar tissue if neurons are damaged due to their 3D anatomy.

Microglia

• Microglia are the phagocytes of the CNS.

• They are the smallest glial cells.

• Functions:

  • Eat up microbes that bypass the blood-brain barrier.

  • Consume debris and waste.

  • They resemble macrophages with pseudopodia to engulf and phagocytose items.

Ependymal Cells

• Ependymal cells are cuboidal to columnar epithelial cells with processes contacting other glial cells.

• They are ciliated to facilitate movement.

• Line ventricles (holes) in the brain and the central canal in the spinal cord.

• They help in circulating and regulating the contents of cerebrospinal fluid (CSF).

• Possess microvilli to absorb substances from the CSF, aiding in monitoring and regulating its contents.

• Have anchoring feet at their base that connect to tissue and other glial cells.

• They are part of the choroid plexus tissue associated with each ventricle.

Oligodendrocyte

• The name means "cells with a few branches".

• These cells myelinate axons in the CNS.

• One oligodendrocyte myelinates multiple axons or segments of axons.

  • This is different from Schwann cells in the PNS, where one cell myelinates only one segment of one axon.

• Myelination by oligodendrocytes significantly increases the speed of action potential conduction along the axons, enabling rapid communication within the CNS.

• They contribute to the structural integrity of the white matter in the brain and spinal cord.

• Disruption of oligodendrocyte function or loss of these cells can lead to demyelinating diseases, such as multiple sclerosis (MS), which impair nerve function and cause various neurological symptoms.