Overview
This lecture introduces different types of glial cells in the nervous system, their locations (CNS vs. PNS), and their key functions, with a focus on astrocytes, microglia, and oligodendrocytes.
Types of Nervous System Cells
- The nervous system includes neurons and glial (neuroglia) cells.
- Glial cells are found in both the central nervous system (CNS: brain and spinal cord) and peripheral nervous system (PNS: nerves outside CNS).
Astrocytes (CNS Glia)
- Astrocytes are star-shaped glial cells found only in the CNS.
- They provide scaffolding to guide neuron growth and positioning.
- Astrocytes remove toxic waste and excess neurotransmitters (e.g., glutamate) from cerebrospinal fluid.
- Astrocytes connect via gap junctions to form a syncytium, sharing and dispersing chemical loads.
- They can transmit signals using calcium waves, helping compartmentalize brain regions.
- Astrocytes form the blood-brain barrier by wrapping around capillaries and reinforcing tight junctions, controlling what enters brain tissue.
Blood-Brain Barrier
- The blood-brain barrier limits direct blood exposure to neural tissue and only allows selective transport of materials.
- Lipid-soluble substances can cross easily; polar molecules need specific transporters.
- The blood-brain barrier is not fully developed in newborns, making them vulnerable to neurotoxins like glutamate.
Microglia (CNS Glia)
- Microglia are small, macrophage-like cells that clean up damaged brain tissue and debris.
Oligodendrocytes (CNS Glia)
- Oligodendrocytes form myelin sheaths around axons in the CNS, increasing the speed of neural signaling.
- Myelin is lipid-rich and essential for effective nerve transmission.
- Diseases that damage myelin (demyelination diseases) are linked to oligodendrocyte dysfunction.
Key Terms & Definitions
- Glial cells — Non-neuronal cells in the nervous system that support and protect neurons.
- Astrocytes — Star-shaped CNS glial cells involved in support, waste removal, compartmentalization, and blood-brain barrier formation.
- Syncytium — A network of interconnected cells sharing chemical loads through gap junctions.
- Blood-brain barrier — A selective barrier that protects brain tissue from direct blood exposure.
- Microglia — Resident macrophage cells of the CNS, clearing debris and damaged cells.
- Oligodendrocytes — CNS glial cells that produce myelin sheaths around axons.
Action Items / Next Steps
- Review functions and differences among CNS glial cells.
- Prepare for upcoming discussion on glial cells of the PNS.
- Ensure understanding of the blood-brain barrier’s role and vulnerability in infants.