Lecture 2- Glia Flashcards
Neuroglia of the CNS
Astrocytes
Oligodendrocytes
Ependymal cells
Microglia
Neuroglia of the PNS
Satellite cells
Schwann cells
Astrocytes
Most numerous
Function
- Recycle neurotransmitters
-Secrete neurotrophic factors that stimulate neuron growth
- Dictate number of synapses formed and modulating synapses according to activity (use i or lose it)
-Maintaining ionic composition
-Formation of the blood-brain barrier
Blood-Brain Barrier
Mediates communication between CNS and periphery
Protects brain from, and regulates transport of neurotoxins and serum factors
Acts more selectively as a transport interface, secretory body and a metabolic barrier
Composition of BBB
Endothelial cells with tight junctions
Thickened basement membrane
Pericytes with contractile proteins
Astrocyte end feet to regulate ions and water
Oligodendrocytes
Form myelin sheaths
Microglia
Intrinsic immune effector cells that underlie the immune response
Ependymal cells
Epithelial-like cells that line the ventricles of the brain and central canal of spinal cord
Schwann cells
Forms myelin sheath
Satellite cells
Envelope cell bodies in autonomic and spinal ganglia with astrocte-like functions
Myelination
Ensheathment of the axon by the glial cell and extrusion of the cytoplasm from parts of the glial cell
Allows for saltatory conduction, therefore increasing speed
Process of myelination
Invagination of a single axon into the support cell which brings its outer membrane into close apposition and seals them together to form a sheet of internal membrane
Support cells wraps numerous layers of mesaxon around axon
Schwann cells myelinate only 1 axon as time, oligodendrocytes myelinate several and remain connected with several inter-nodes via cytoplasmic bridges
Process of regeneration and repair
As it is severed, distal portion begins to degenerate as a result of protease activity
Cytoskeleton begins to breakdown, followed by dissolution of the cell membrane
Axonal regeneration in PNS
Regeneration in PNS
Cytoskeleton and membrane degrade
Schwann cells that surround axons at the distal ends shed their myelin
Phagocytotic cells (macrophages) clear myelin and axon debris and produce cytokines which enhance axon growth
Regeneration begins proximally to distally
New axons sprout from nodes of Ranvier
2-5mm per day
Regeneration in the CNS
Macrophages infiltrate more slowly, therefore delaying removal of inhibitory myelin
Cell adhesion molecules at distal end are not upregulated as much as in the PNS, limiting macrophage recruitment
Astrocytes proliferate similar to Schwann cells but instead become “reactive astrocytes” which produce glial scars and inhibit regeneration
