Neuron :Supporting cells :CNS : neuroglia (glia)PNS : Schwann cells and satellite cellsFunctions :physical supportelectrical insulationmetabolic exchangeblood-brain barrierComposition of Nervous TissueComposition of Nervous TissueTypes and Functions of GliaName of Glial CellFunctionAstrocyte (Astroglia)Star-shaped cells that provide physical and nutritional support for neurons: 1) clean up braindebris; 2) transport nutrients to neurons; 3) hold neurons in place; 4) digest parts of dead neurons; 5) regulate content of extracellular space MicrogliaLike astrocytes, microglia digest parts of dead neurons.Oligo-dendrogliaProvide the insulation (myelin) to neurons in the central nervous system.Satellite CellsPhysical support to neurons in the peripheral nervous system.Schwann CellsProvide the insulation (myelin) to neurons in the peripheral nervous system.Neuroglia Neuroglia in the CNSin the CNSAble to replicate!Importance in nervous system function is VASTLY underestimated!Evidence is mounting: Nurturing roleSignaling role (Memory?)InflammationPainMany more to come!Neuroglia: Neuroglia: Distinguishing Distinguishing FeaturesFeatures1.Presence of tight junctions between the endothelial cells2.One of the notable features of endothelial cells in comparison to other cell is the lack of pinocytic vesicles3.Selective permeability to molecules based on their molecular weight and lipid solubility4.Presence of specific markers5.Rich in two enzymes: gamma glutamyl transpeptidase (GGTP) (for amino acid transport) and alkaline phosphatase (transport of phsopahte ions) used as marker for BBB.6.Others: glucose transporter (GLUT-1); endothelial barrier antigen (EBA; unknown function) and antigen recognized by the MRC OX-47 monoclonal antibody (important for cell-to-cell adhesion); transferrin receptor (transport of ferric ions).Properties of Blood Brain BarriersProperties of Blood Brain BarriersBBBBBB1. Neurons have TWO processes called axons and dendrites. Glial cells only have ONE. 2. Neurons CAN generate action potentials. Glial cells CANNOT, however, do have a resting potential. 3. Neurons HAVE synapses that use neurotransmitters. Glial cells do NOT have chemical synapses. 4. Neurons do NOT continue to divide. Glial cells DO continue to divide. 5. There are many MORE (10-50 times more) glial cells in the brain compared to the number of neurons.Glia are different from neurons:Glia are different from neurons:Nerve CellsNerve CellsNeurons, Glia, Neurons, Glia, Extracellular Space, Extracellular Space, and Bloodand BloodBidirectional Communication Partners Bidirectional Communication Partners in the CNSin the CNSReceiving signals from neighboring neurons and responding to them with release of neuroactive substancesExpress receptors for almost all neurotransmitters and neuromodulatorsIncrease of intracellular calcium concentrationMembrane depolarization in astrocytes are common responses to neural activityMetabolically coupled to neural activityMetabolism of Astrocytes and their Metabolism of Astrocytes and their Metabolic Cooperation with NeuronsMetabolic Cooperation with Neurons Glucose Amino acid metabolism Enzymes:glutamine synthetase(glutamate-glutamine cycle);glycogen phosphorylatase (glycogen mobilization); pyruvate carboxylase (anaplerotic synthesis of oxaloacetate); cysteine sulfinate decarboxylase (synthesis of taurine); glycine cleavage system, glycine metabolism. Three Types of Metabolic Three Types of Metabolic Cooperation of Astrocytes and Cooperation of Astrocytes and NeuronsNeurons1.Supply of the energy substrate lactate to neurons2.The recycling of neuronal glutamate by the glutamate-glutamine cycle3.The supply by astrocytes of precursors for neuronal glutathione (GSH) synthesis