Part 2 – Glial Cell Functions, Neuron Anatomy, Axon Transport & Myelin Sheaths

What is the function of astrocytes?

They support and brace neurons, anchor them to nutrient supplies, and help control the chemical environment around neurons by regulating ion and neurotransmitter levels.

Where are astrocytes found?

In the Central Nervous System (CNS).

How do astrocytes contribute to the blood–brain barrier?

Their end-feet wrap around capillaries, helping control what substances enter the brain tissue.

What additional roles do astrocytes play?

They influence neuronal growth, repair damaged tissue, and help recycle neurotransmitters.

What are microglia?

Small, thorny glial cells in the CNS that act as macrophages.

What is the function of microglia?

They monitor neuron health and phagocytize microorganisms, debris, and dead neurons.

Why are microglia important?

Because immune cells have limited access to the CNS, microglia provide the brain’s main defense system.

What are ependymal cells?

Ciliated glial cells lining the central cavities of the brain and spinal cord.

What is the function of ependymal cells?

They form a permeable barrier between cerebrospinal fluid (CSF) and the nervous tissue and help circulate CSF with their cilia.

What are oligodendrocytes?

Glial cells in the CNS that wrap their extensions around nerve fibers.

What is the function of oligodendrocytes?

They form the myelin sheath around CNS axons, providing electrical insulation and speeding impulse conduction.

What are satellite cells?

PNS glial cells that surround neuron cell bodies in ganglia.

What is the function of satellite cells?

They regulate the environment around neuron cell bodies, similar to astrocytes in the CNS.

What are Schwann cells?

Glial cells in the PNS that surround and myelinate axons.

What is the function of Schwann cells?

They form the myelin sheath in the PNS and assist in regeneration of damaged peripheral nerve fibers.

What is the cell body (soma) of a neuron?

The biosynthetic center containing the nucleus and organelles.

What organelles are prominent in the soma?

Rough endoplasmic reticulum (Nissl bodies) and mitochondria for high metabolic activity.

What are Nissl bodies?

Rough endoplasmic reticulum clusters that synthesize proteins for neuron maintenance and repair.

What are dendrites?

Short, branching extensions that receive input and convey electrical signals toward the cell body.

What are axons?

Long processes that transmit impulses away from the cell body toward other neurons or effectors.

Where do most axons arise from?

A cone-shaped region of the soma called the axon hillock.

What is the axon terminal?

The knoblike distal endings of an axon that release neurotransmitters into a synapse.

What are axon collaterals?

Occasional branches along the length of an axon that allow communication with multiple targets.

What are telodendria?

Fine terminal branches of an axon ending in synaptic terminals.

What is axonal transport?

The movement of materials between the cell body and axon terminals.

What are the two types of axonal transport?

Anterograde (from soma to terminal) and retrograde (from terminal to soma).

What substances move by anterograde transport?

Mitochondria, membrane components, and enzymes.

What substances move by retrograde transport?

Organelles for recycling, signaling molecules, and viruses such as herpes and rabies.

What is myelin?

A fatty, segmented sheath around most long axons.

What is the purpose of myelin?

It protects and electrically insulates fibers, increasing the speed of nerve impulse transmission.

How is myelin formed in the CNS?

Oligodendrocytes wrap extensions of their plasma membranes around multiple axons.

How is myelin formed in the PNS?

Schwann cells wrap themselves completely around a single axon segment, forming concentric layers.

What is a neurilemma?

The outermost layer of the Schwann cell that contains the nucleus and cytoplasm.

What are nodes of Ranvier?

Gaps between adjacent Schwann cells where the axon membrane is exposed.

What occurs at the nodes of Ranvier?

Voltage-gated ion channels are concentrated there, allowing saltatory (jumping) conduction of action potentials.

What is white matter?

Regions of the CNS containing dense collections of myelinated fibers.

What is gray matter?

Regions of the CNS containing neuron cell bodies, dendrites, and unmyelinated fibers.

What is the functional significance of myelin thickness?

Thicker myelin increases conduction velocity and efficiency of impulse transmission.

What happens to damaged myelin in the CNS?

It cannot regenerate effectively; oligodendrocyte damage leads to disorders such as multiple sclerosis (MS).