1. HISTOLOGY 1.14.: NERVOUS TISSUE: GLIAL CELLS
Neuroglia comprise over 90 % of the cells of the nervous system.
Glial cells are relatively small.
Their function is to provide structural support
form the CNS boundary
ensheath and insulate axons
maintain the ionic homeostasis of the extracellular space
phagocyte cell debris
produce scar tissue
Classification of neuroglia:
in the central nervous system (CNS): ependyma
astrocytes
oligodendrocytes
microglial cells
in the peripheral nervous system (PNS): neurolemmocytes: Schwann cells
satellite cells

2. Neuroglia of the CNS: ependymal cells
Ependymal cells line ventricular cavities in the brain
and the central canal of the spinal cord.
They are cuboidal or columnar cells tightly packed together.
Their luminal surface is ciliated and microvilliated.
The cerebrospinal fluid is produced by modified ependymal cells
(choroid plexus) EM LM

3. Neuroglia of the CNS: astrocytes
They have the largest nuclei among glial cells.
They are stellate-shaped with numerous processes:
in the white matter: long slender processes: fibrous astrocytes
in the gray matter: shorter branching processes: protoplasmic astrocytes.
They contain glial fibrillary acidic protein (GFAP) forming glial filaments.
Astrocyte processes form expanding endfeets which adjoin into limiting
membranes:
membrana limitans gliae superficialis (at the surface of CNS)
membrana limitans gliae perivascularis (blood-brain barrier).
Astrocytes provide structural support,
form diffusion barriers around synapses,
take up extracellular potassium ions
are capable of phagocytosis
proliferate to form a scar in the case of injury

4. Schematic drawing of a protoplasmic astrocyte:
Nucleus
Glial filaments
Not found
Capillary
Endfeet of the astroglia around capillary
Basal lamina of the capillary endothelium
Endfeet around a synapse
Presynaptic terminal
Spiny dendrite
Myelinated axon
Initial segment of an axon
Axo-axonic synapse
Axospinous synapse
Dendritic spine

5. Neuroglia of the CNS: oligodendrocytes
They have small spherical nuclei in routinely stained sections.
Their processes are thin and difficult to visualize.
Their function in the gray matter is perineuronal satellite-like, in white
matter they form the myelin sheaths around axons. LM
Oligodendrocyte
Tapering process of oligodendrocyte
Axon
Myelin sheath
Synapse at node of Ranvier
Soma of a neuron
Axon hillock
Synaptic boutons

6. Neuroglia of the CNS: microglia
Microglia are cells of mesodermal origin that invade the CNS
when it is vascularized.
They have antigen presenting and phagocytic abilities.
They have small elongated chromophilic nuclei.
Other cell types in the CNS
with phagocytotic activity:
astrocytes,
oligodendrocytes,
pericytes,
hematogenous macrophages
Silver impregnation

7. Neuroglia of the PNS: neurolemmocytes
They are glial cells responsible for the myelination of peripheral axons
(Schwann cell), or encapsulate neuronal cell bodies as satellite cells.
They provide a protected immediate environment for PNS neurons.
They can become phagocytic upon nerve damage.
Cross-section of a myelinated
peripheral axon at the level of
a Schwann cell nucleus EM LM
Schwann cells (arrows)

8. Satellite cells ( yellow arrow and
no. 3) around a pseudounipolar
neuron from the spinal ganglion

9. NERVE FIBERS: MYELINATED AXONS
Node of Ranvier LM EM LM
Red arrow: outer mesaxon
Blue arrow: inner mesaxon
Small red arrow: neuro-
filament
Small blue arrow: micro-
tubulus EM
Cross-section
Longitudinal section

10. NERVE FIBERS: NON-MYELINATED AXONS
Schwann cell nucleus
Mesaxon
Cross-section of the axon

11. Structure of a peripheral nerve
1-6. Layers of epineurium
7. Myelinated fiber with Schwann cell
8. Non-myelinated fibers in a Schwann
cell
9. Capillary
Endoneurium
12. Perineurium
13. Fibrocyte