Neuroglia/Histology

Neuroglia abundance

glia constitute a substantial proportion of CNS cells; he ratio of glia to neurons varies by region and species

Neuroglia morphology

generally smaller than neurons; routine HandE staining typically shows only their nuclei

Neuroglia prolifereation

unlike most mature neurons, some glial cells retain the abililty to divide throughout life

Neuroglia function

provide structural, metabolic, and protective support to neurons

Astrocytes

structural and metabolic support; maintain homeostasis

Oligodendrocytes

Form myelin around CNS axons

Microglia

immune defense and removal of cellular debris

Ependymal cells

line CNS cavities; aid CSF circulation

PNS neuroglia; Schwann cells

Myelinate PNS axons; support regeneration

PNS Neuroglia; Satellite cells

surround neuronal cell bodies in ganglia

Specialized ependymal cells inchoroid plexus

contribute to CSF production

Astrocytes function

-regulate extracellular K+, neurotransmitter, and pH

-Provide metabolic support and help maintain the blood-brain barrier (release signaling factors: GDNF)

-participate in synaptic regulation and tissue repair

Capillary endothelial cells

form the BBB through specialized tight junctions

Glucose transport

facilitate glucose uptake through GLUT1 transporters to support neuronal metabolixm

glycogen storage

store glycogen as an energy reserve for periods of increased neuronal activity

Metabolic support of axons

supply neurons with energy substrates, including lactate

Neuronal survival axon function

release neurotrophic factors, including nerve growth factor that support neuronal maintenance and survival

Astrocytes prevent

glutamate excitotoxicity

Glutamate

major excitatory neurotransmitter in the CNS; released from presynaptic axon terminals during neuronal signaling

Excitotoxicity

Excess extracellular glutamate causes prolonged receptor activationa nd neuronal injury

How do astrocytes remove excess glutamate?

through EAAT1/EAAT2 transporters

Gluatamte recycling:

convert glutamate to glutamine, which is returned to neurons for neurotransmitter synthesis

Microglia abundance

approximately 5-20$ of CNS glial cells varying by region and species

Microglia immune surveillance

resident immune cells that monitor CNS tissue

Microglia activation

respond to injury or infection by changing morphology and function

Microglia proliferation

can multiply locally following tissue injury

Microglia phagocytosis

engulf damaged cells, pathogens, and cellular debris

Microglia inflammation

releases cytokines that regulate immune responses

Oligodendrocytes (CNS)

-constitute approximately 20-30% of CNS glial cells, varying by region

-Form myelin sheaths around CNS axons

-a single oligodendrocyte can myelinate multiple axon segments

Schwann Cells (PNS)

-Myelinate axons in the peripheral nervous system

-Each myelinating Schwann cell forms one myelin segment of a single axon

-Support peripheral nerve repair and regeneration

Myelin sheath

-formed by repeated wrapping of glial cell membranes around axons

-electrically insulates axons and increases conduction velocity through saltatory conduction

Axon contact

glial cell processes extend and surround the axon

Membrane wrapping

the glial membrane repeatedly wraps around the axon, forming multiple layers

Myelin compaction

most cytoplasm is displaced between membrane layers, forming a compact myelin sheath

Myelination

electrically insulates axons and increases the speed of nerve impulse conduction; increases membrane resistance and decreases capacitance, accelerating impulse propagation

Larger axons

have lower internal resistance, allowing faster conuction

Saltatory conduction

Action potentials are regenerated at the nodes of Ranvier, enabling rapid transmission