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Nervous System Glial Cells Reference Cheat Sheet
A printable reference covering CNS glia, PNS glia, myelination, support roles, and nervous system protection for grades 10-12.
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Glial cells are the support cells of the nervous system, but they do much more than hold neurons in place. This cheat sheet helps students compare the major glial cell types in the central nervous system and peripheral nervous system. It is useful for understanding brain function, nerve repair, myelination, and how neurons stay healthy. Students in grades 10 to 12 need these comparisons because glial cells often appear together but have different locations and jobs. The core idea is that neurons send signals, while glia protect, nourish, insulate, clean, and regulate the environment around neurons. CNS glia include astrocytes, oligodendrocytes, microglia, and ependymal cells. PNS glia include Schwann cells and satellite cells. Myelin increases signal speed by insulating axons and allowing action potentials to jump between nodes of Ranvier.
Key Facts
- CNS glia are found in the brain and spinal cord, while PNS glia are found in nerves and ganglia outside the brain and spinal cord.
- Astrocytes support neurons, help form the blood-brain barrier, regulate ions and neurotransmitters, and guide repair after injury.
- Oligodendrocytes form myelin in the CNS, and one oligodendrocyte can myelinate segments of several different axons.
- Schwann cells form myelin in the PNS, and one Schwann cell myelinates one segment of one axon.
- Microglia act as immune cells in the CNS by detecting damage, removing debris, and responding to infection or inflammation.
- Ependymal cells line brain ventricles and the central canal of the spinal cord, and they help produce and circulate cerebrospinal fluid.
- Myelination rule: more myelin generally means faster nerve impulse conduction along an axon.
- Saltatory conduction means an action potential jumps from node of Ranvier to node of Ranvier, which increases conduction speed and saves energy.
Vocabulary
- Glial cell
- A non-neuron nervous system cell that supports, protects, nourishes, or insulates neurons.
- Astrocyte
- A star-shaped CNS glial cell that supports neurons, regulates the extracellular environment, and contributes to the blood-brain barrier.
- Oligodendrocyte
- A CNS glial cell that forms myelin around axons in the brain and spinal cord.
- Schwann cell
- A PNS glial cell that forms myelin around peripheral axons and helps damaged peripheral nerves regenerate.
- Microglia
- A CNS immune glial cell that removes pathogens, damaged cells, and cellular debris.
- Myelin sheath
- A fatty insulating layer around an axon that increases the speed of electrical signal transmission.
Common Mistakes to Avoid
- Saying glial cells are just filler cells is wrong because glia actively regulate neuron survival, signaling, immunity, and insulation.
- Confusing oligodendrocytes with Schwann cells is wrong because oligodendrocytes myelinate axons in the CNS, while Schwann cells myelinate axons in the PNS.
- Assuming one myelinating cell always covers an entire axon is wrong because myelin is divided into segments separated by nodes of Ranvier.
- Forgetting that microglia are immune cells is wrong because their main role is defense, cleanup, and response to injury in the CNS.
- Thinking myelin creates the nerve impulse is wrong because neurons generate action potentials, while myelin mainly speeds conduction and reduces signal loss.
Practice Questions
- 1 A neuron in the spinal cord has myelin on its axon. Which glial cell most likely made that myelin?
- 2 A peripheral nerve axon has 12 myelinated segments. If each segment is made by one Schwann cell, how many Schwann cells are needed?
- 3 One oligodendrocyte myelinates 4 axon segments. How many axon segments could 6 oligodendrocytes myelinate in total?
- 4 Explain why damage to myelin can slow communication in the nervous system even if the neuron itself is still alive.