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Download - Describe the roles of the different types of glial cells
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- Describe the roles of the different types of glial cells - there are 3 types of glial cells: astrocytes, schwann cells/oligodendrocytes and microglial cells. - Astrocytes have multiple functions. One function is helping to keep the integrity of the BBB. Astrocytes’ feet wrap around the capillaries in the brain to further tighten up the tight junctions and prevent any leakage of unwanted substances into the brain. This helps create a very finely and tightly regulated environment and keeps out any potential toxins. Astrocytes also release various neurotrophic factors which regulate axonal growth and neuronal transport - Schwann cells and oligodendrocytes form the myelin sheath around neurons which insulates the axon and helps increase conduction speed in the axon. Neurons which have become demyelinated can be so due to autoimmune diseases like MS and this interferes with proper conduction of signals. - Microglial cells are the immune cells of the CNS. They respond to insult or injury by changing their morphology and number. However, excessive activation is deleterious and can contribute to degeneration. – Identify the key cellular features of a neuron, include the locations of VGIC, LGIC, GPCR, Transporters, myelin sheath, dendrites, axon, soma - Soma – cell body of a neuron. This is where the DNA is stored and proteins are manufactured. Can have some axons/dendrites synapsing onto the cell body where total signals are then added and this determines whether the signal will be sent down this axon too – only if it reaches over the threshold - Axon – the part of the neuron that transmits signals to other neurons. Covered in a myelin sheath with Nodes of Ranvier between big chunks of insulation. These nodes are densely packed with transporters and ion channels so the voltage/depolarization skips from node to node - Dendrites – branches of a neuron and can synapse with other dendrites, axons or cell bodies. Pass the signal downwards to the cell body and then axon - Myelin sheath – insulation of the axon made of multiple layers of membrane. Made from Scwann/oligodendrocyte cells. This allows faster conduction speeds and stops ‘leakage of the signal’. Damaged in some diseases like MS. Can also be damaged by drugs - Transporters – located on presynaptic terminals or astrocytes. These take up the NT after it has been released and facilitate its quick removal from the synapse. This is important as NT concentrations can rise from nM to mM following an AP and some NTs like glutamate can cause excitotoxicity and need to be quickly removed. Some rely on conc gradients of other substances. Family 1 transports (GABA, glycine, 5HT, dop etc) use 1-3Na and Cl- while family 2 transporters used for glutamate and aspartate use 3Na+, H+ and K+ to transport NT (very powerful). - GPCR – g protein coupled receptors are located postsynaptically and are activated based on a signal that is communicated by the release of NT. They are 7 transmembrane domain proteins and the alpha subunit (either alpha I, s or q) acts on adenylate cyclase to either inhibit (i) or stimulate (s) it. The betagamma subunit acts on other enzymes and proteins - LGIC – ligand gated ion channels use the NT to bind and then open a central pore in the channel which allows the particular ion to pass through. These channels have immediate responses and are also often located postsynaptically e.g. nAChRs VGIC – voltage gated ion channels are opened and activated by voltage. E.g. Ca2+ vg ion channels are located presynaptically. When the current comes it activates these