3.6 Overview of Glial Cells and Their Functions

Overview of Brain Cells

  • The brain is not made up entirely of neurons but contains various types of cells that play essential roles in brain function.

Types of Glial Cells

  • Glial cells, or neuroglia, are the most abundant cells in the brain, serving as support cells for neurons.

  • Glial cells are not a single type but include several types:

    • Microglia

    • Function: Act as the brain's immune cells.

    • Role: Remove debris, dead cells, and pathogens.

    • Analogy: Considered the "bodyguards" of neurons, they respond to injury by clearing out waste and mounting defensive responses against pathogens.

    • Oligodendrocytes

    • Function: Produce myelin, which is essential for the conduction of electrical impulses along axons.

    • Process: They create extensions that wrap around axons to form myelin sheaths, thus facilitating faster signal transmission.

    • Astrocytes

    • Function: Provide physical support to neurons and maintain the environment around them.

    • Historical View: Initially thought that astrocytes made up most of the brain's glial cells. The term "glial" translates to "glue" in Latin, emphasizing their supportive role.

    • Responsibilities: Help to deliver nutrients and energy to neurons, promoting their health and function.

Role of Glial Cells in Disease

  • Glial cells are implicated in neurodegenerative disorders such as multiple sclerosis (MS).

    • Process in MS:

    • The immune response, regulated by microglia, mistakenly targets myelin produced by oligodendrocytes.

    • This leads to the destruction of myelin, which is erroneously labeled as a foreign pathogen by the immune system.

Effects of Myelin Damage

  • Myelin's Role in Electrical Signal Conduction:

    • Saltatory Conduction:

    • Definition: The process by which electrical impulses "jump" from one node of Ranvier to another.

    • Mechanism: Myelin sheaths create nodes of Ranvier, allowing impulses to skip the myelinated portions of the axon, resulting in faster signal transmission.

    • Consequences of Myelin Loss:

    • If microglia destroy myelin, neurons experience slower electrical signal transmission.

    • This deterioration affects neuronal communication, leading to a range of functional impairments.

Implications of Glial Cell Dysfunction

  • Progressive Damage and Functional Impairment:

    • The specific type of functional impairment varies depending on the areas of the brain affected by the damage.

    • Common outcomes include:

    • Deterioration of basic functions like swallowing and movement control.

    • Loss of independence as the disease progresses, often requiring assistance for daily living activities.