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• The presynaptic plasmalemma has electron-dense plaques along its
cytoplasmic surface. Synaptic vesicles tend to cluster around these regions.
The presynaptic telodendria may assume one of the following shapes:

• Terminal bulbs or boutons: the axon terminates as bulbous enlargement.
• Passage synapse: some telodendria have multiple preterminal bulbs that form

several synapses along its course.
• Calyx synapse: the telodendria are calyx-like and embrace the postsynaptic

structure.
Synaptic cleft

• The presynaptic membrane is separated from the plasma membrane of the
opposed neuron or effector cell by a narrow intercellular gap of uniform width
(20-30 nm) called the synaptic cleft.

• The cleft contains a protein-carbohydrate substance that may serve to hold pre-
and-post-synaptic membranes in apposition.

Postsynaptic membrane

• It is the cell membrane of the adjacent neuron and it may have thicker
accumulation of electron-dense substance. It is not associated with synaptic
vesicles.

• The cytoplasm beneath the postsynaptic membrane often contains a network of
fine fibrils known as the postsynaptic web that forms desmosome-like
structures that help to maintain the integrity of the synapse.

NEUROGLIA

• They are a group of highly branched cells that occupy the spaces between
neurons providing both mechanical and metabolic support. They are all derived
from the ectoderm, except microglia that is mesodermal in origin.

Neuroglia of the CNS

Oligodendrocytes (Oligodendroglia) (Oligodendroglia, oligos, small,
dendron, tree)

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