Neuroglia: Supporting Cells of the Nervous System

Neuroglia (glia): These are the supporting cells of the nervous system, making up approximately 90% of the cells.
Function: Protect, nourish, and support neurons and their surrounding environment.
Types in CNS: Astrocytes, microglia, ependymal cells, and oligodendrocytes.
Types in PNS: Satellite cells and Schwann cells.
Key Difference from Neurons: Glia can divide and reproduce, which is crucial for maintaining a healthy nervous system.

Origin of Name: "Micro-" meaning small.
Function: Part of the defense system within the central nervous system.
Role: Act as patrolling scavenger cells.
Structure: Multiple processes extending from the cell body to sense threats in the extracellular space.
Mechanism: Use phagocytosis to ingest and digest potentially threatening particles, thus removing the threat.
Involvement: Involved in inflammatory processes in the central nervous system.

Shape: Star-shaped, hence the name.
Function: Provide structural and chemical support and protection to neurons.
Structure: Multiple processes extending from the cell body (larger than microglia).
Two Main Roles:
- Blood-Brain Barrier (BBB): Astrocytes form a structural part of the BBB. Blood vessels are made of endothelium, a single layer of squamous epithelial cells. Astrocytes provide an additional layer of structural barrier, regulating substances entering the CNS from the systemic circulation.
- Neuronal Communication: Astrocytes protect the conversation between neurons at synapses (the meeting points of neurons), where chemical communication occurs via neurotransmitters.
Synaptic Function:
- Monitoring: Astrocytes hover around synapses, ensuring neurotransmitters bind correctly and monitoring their concentration.
- Regulation: They absorb excess neurotransmitters and regulate the concentration of ions and other molecules in the extracellular space around neurons.
Glial Scar Formation:
- Repair: When neurons in the CNS are damaged (neurons have minimal regeneration capability), astrocytes form glial scars to repair but not regenerate nervous tissue.

Location: Peripheral nervous system.
Role: Similar to astrocytes; they protect and support neuronal cell bodies in the PNS.
Structure: Sit on top of neurons or neuronal cell bodies.

Function: Form ependyma, which are specialized structures that produce cerebrospinal fluid (CSF).
Location: Line the ventricles (empty spaces) of the brain and spinal cord.
Mechanism:
- Secretion: Secrete CSF into the ventricles.
- Circulation: Aid in the circulation of CSF in the CNS.
- Structure: The apex of the cell faces the ventricle, and they have cilia to help move fluid along the surface.

Location: Central nervous system.
Function: Produce myelin, a protein-lipid complex that wraps around axons of neurons.
Role: Ensure the protection and maintenance of electrical signals flowing through neurons, thus maintaining neuronal communication.
Mechanism: Processes extend from the cell body and attach to multiple axons (up to 15).
Analogy: Similar to Spider-Man shooting webs, the processes wrap around axons to protect and myelinate them.

Location: Peripheral nervous system.
Function: Same as oligodendrocytes; they produce myelin and coat axons of neurons forming nerves in the PNS.
Difference from Oligodendrocytes: One Schwann cell myelinates a single axon.
Regenerative Capacity: Schwann cells possess a limited regenerative capacity, allowing some regeneration of damaged neurons/axons in the PNS.
Regeneration Comparison: Unlike oligodendrocytes, which cannot provide similar service in the CNS (damage is generally irreparable).

Central Nervous System:
- Microglia
- Astrocytes
- Oligodendrocytes
- Ependymal cells
Peripheral Nervous System:
- Satellite cells (similar to astrocytes)
- Schwann cells (similar to oligodendrocytes; make myelin and insulate axons)