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From the simple to the complex
Anatomy by Level of Organization

HelpLinked Module: Some types of synaptic specializations of dendrites. Linked Module: Tutorial 2: External Components of a NeuronLinked Module: Parts of the Nerve Cell and Their Functions
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History Module: La découverte du neuroneHistory Module: The discovery of the neuron

The Variety and Structural Complexity of Neurons

The next time you take a walk in the woods in the wintertime, take a good look at the trees and notice how similar they are in structure to neurons. The trees’ branches are like dendrites, and the buds on these branches are like dendritic spines. The trees’ trunks are like axons, and their roots are like the axons’ numerous terminal buttons.

From there it should be just a small leap to imagine that you are taking a wintertime stroll right through the middle of your own brain.


Neurons form networks through which nerve impulses travel. From each neuron’s dendrites to the sometimes very distant tip of its axon, these impulses propagate through the neural membrane in the form of electricity.

But because the neurons communicate with one another without touching one another, they use special molecules called neurotransmitters to pass nerve impulses from one neuron to the next.

This chemical transmission of nerve impulses causes the axon and the dendrites to develop specialized structures that facilitate it.

Thus, dendrites have thousands of “spines” sticking up out of their surface.

The bulb-like terminal buttons of the axons, which secrete the neurotransmitters, are positioned opposite these spines.

But the form of these component structures of the synapse varies tremendously, as does the overall form of the neurons themselves.

A neuron’s connections from and to other neurons.


Linked Module: Astrocyte electron microscopy pictureLinked Module: Microglia electron microscopy pictureLinked Module: Oligodendrocyte electron microscopy pictureLinked Module: Tutorial 4: Shapes and Roles of Glial Cells
Linked Module : La microglie impliquée dans le système immunitaire du cerveau Linked Module: Les composantes du systèmes nerveuxLinked Module  Les cinq résultats qui comptent

Glial Cells Too Are Sensitive to the Environment


Various types of glial cells, each in its own way, help the neurons of the central nervous system to function properly.

  • Star-shaped astrocytes provide neurons with mechanical support, supply them with nutrients, and maintain the equilibrium of the extracellular environment. They also digest and eliminate all kinds of debris.

  • The microglial cells constitute the first line of defence against foreign invaders. They are the macrophages of the brain.

Linked Module: La microglie impliquée dans le système immunitaire du cerveau (video from the program Découverte)

  • The oligodendrocytes form the myelin sheath that surrounds the axons of many neurons. The very special way in which the oligodendrocytes wrap around the axons accelerates neural conduction.

The glial cells that perform these same functions in the peripheral nervous system have different names. The glial cells that provide mechanical support are called satellite cells, while those that manufacture myelin are called Schwann cells.

But of all the glial cells, the astrocytes are probably the ones whose functions are the most complex.

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