🧫 Nervous System Lesson

AMOS EP: six glial cell types

Glial cells outnumber neurons 10 to 1 — these support cells do the essential background work that makes neuron function possible.

Astro.

Microgl.

Oligo.

Schwann

Ependym.

Peripheral

📖 Full Breakdown

Six glial types, split between the CNS and PNS, each with a specialized job

Four types work in the CNS; two types work in the PNS — a clean division worth memorizing alongside each cell's function.

Astrocytes (CNS)

Blood-brain barrier and nutrient support

Provide structural support and help maintain the blood-brain barrier, regulating what substances can pass from blood into brain tissue.

Microglia (CNS)

The immune cells of the CNS

Function as the CNS equivalent of macrophages, phagocytosing pathogens and cellular debris.

Oligodendrocytes (CNS)

Myelinate CNS axons — one cell, multiple axons

A single oligodendrocyte myelinates SEVERAL different axons simultaneously — this cell type is specifically damaged in multiple sclerosis.

Ependymal cells (CNS)

Produce and circulate CSF

Line the ventricles of the brain and are responsible for producing cerebrospinal fluid.

Schwann cells (PNS)

Myelinate PNS axons — one cell per axon

Unlike oligodendrocytes, each Schwann cell myelinates only ONE axon segment — this different one-to-one relationship is part of why the PNS can regenerate after injury.

Satellite cells (PNS)

Support neurons within PNS ganglia

Provide structural and metabolic support to neuron cell bodies located in peripheral ganglia.

🩺 Clinical / Exam Application

A patient with multiple sclerosis develops progressive neurological symptoms as their body's immune system attacks oligodendrocytes, destroying the myelin sheaths these cells maintain around CNS axons. Because a SINGLE oligodendrocyte myelinates multiple axons at once (unlike Schwann cells in the PNS, which myelinate just one axon each), damage to relatively few oligodendrocytes can disrupt signal transmission across a disproportionately large number of axons — helping explain why MS can produce such widespread, seemingly unrelated neurological symptoms from what is fundamentally a single type of cell damage.

⚠️ Exam Alert

The one-cell-multiple-axons (oligodendrocytes, CNS) versus one-cell-one-axon (Schwann cells, PNS) distinction is frequently tested, since it directly relates to why CNS myelin damage (as in MS) can be so functionally devastating compared to more localized PNS nerve damage.

🚧 Common Trap

Don't assume all six glial cell types perform the same "support" function in the same way. Astrocytes, microglia, oligodendrocytes, and ependymal cells all have genuinely distinct jobs (barrier maintenance, immune defense, myelination, and CSF production respectively) — "glial cell" is a broad category covering very different specialized functions.

✅ Quick Check

Why can damage to a relatively small number of oligodendrocytes in multiple sclerosis affect a disproportionately large number of axons?

📝 Exam Prep

Common Exam Questions

❓ What are the main glial cell types in the CNS and PNS?

✅ CNS glial cells include astrocytes (blood-brain barrier), microglia (immune cells), oligodendrocytes (myelination), and ependymal cells (CSF production). PNS glial cells include Schwann cells (myelination) and satellite cells (support neurons in ganglia).

❓ What is the key structural difference between oligodendrocytes and Schwann cells?

✅ A single oligodendrocyte (CNS) myelinates multiple axons, while each Schwann cell (PNS) myelinates only one axon segment — this difference is part of why the PNS has better regenerative capacity than the CNS.