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Biological Sciences
Stefan Rusyniak

LECTURES 10 & 11 – NERVOUS TISSUES Cells of the CNS GLIAL CELLS EPENDYMAL NEURON Oligodendr- Astrocyte MICROGLIA CELLS ocyte Structure - Cell body (soma or perikaryon), nucleus, - Cell body - Largest neuroglial cells - Smallest - Form a simple axon, dendrites, abundant Nissl substance separate from neuroglial cells columnar (RER), myelin myelin - Oval cell bodies covering the - Myelin - Nucleus - Believed to ventricles of the  Protects and insulates nerve fiber - Unbranched originate in the CNS (axon) cytoplasmic bone marrow - In contact with  Helps speed up transmission of processes - Part of the astrocytes  impulse – salutatory conduction Mononuclear forms a barrier  Composition: 70-80% lipid, and Phagocyte System - Not true some protein  made from a (MPS) basement - Originate from membrane cellular membrane monocytes - Have surface  In the CNS, is generated by oligodendrocytes cilia and  In the PNS, is generated by microbilli Schwann cells Nucleus Large, very pale nucleus (lots of Oval Small, elongated euchromatin) with a dense nucleolus nucleus, nucleus (Owl’s eye nucleus) clear space around nucleus Processes - Cellular processes not normally visible Un-branched Short, “spiny” (not all neurons look the same) cytoplasmic processes  - Many, short highly branched dendrites processes processes appear to - One axon – transmits action potential to wrap around have small spikes other cells/neurons nerve fibers  A single - Dendrites cell can thus  Short afferent processes produce  Variable diameter along length – it several internodes changes  May display Nissl substance  Unmyelinated  Some have „dendritic spines‟  important for proper brain development; highly elongated in young people and shorten with age - Axon  Axon Hillock is normally free of any ribosomes or RER = poor staining  Initial Segment follows  Less Nissl substance, pale  Diameter affects speed of impulse transmission  diameter more uniform throughout  More mature than dendrites  Can be myelinated (increases action potential speed) or unmyelinated (does not mean “naked”)  Can have collateral braches  End in telodendria and terminal boutons at the synapse Abundance 10% of cells in the CNS 90% of cells 90% of cells in the CNS Not common or in the CNS easily identifiable on slides Different 1) Unipolar: Other cell‟s axons terminate 1) Protoplasmic Astrocytes Types on the cell body  no dendrites, one  Found mostly in gray axon matter 2) Bipolar: A single dendrite enters the cell body (can still have an extensive  Have many short, dendritic tree) and a single axon leaves broad, branched 3) Multipolar: Many dendrites enter the cellular processes cell body, one axon leaves  Sometimes described 4) Pseudounipolar: Cell body looks as “mossy” unipolar, but afferent and efferent 2) Fibrous Astrocytes fibers merge before entering the cell  Found mostly in white body matter  Have fewer processes (long and slender) Function - Axonal transport: retrograde (to cell - Produces 1) Support blood vessels and - Have phagocytic - Involved in body) and anterograde (to termini) myelin neurons  may play a properties the secretion of sheath in the role in transferring - Their activity is CSF CNS metabolites (nutrients) and somewhat (cerebrospinal - Doesn‟t wastes between blood controlled by fluid) support the stream and neurons  astrocytes - Surface cilia axon controls - Equivalent to the help circulate metabolically microenvironment macrophage of the CSF 2) Appear to be involved in CNS - Microvilli aid the blood-brain barrier in absorption of production  have large the CSF “perivascular feet” which terminate on blood vessel walls 3) Takes up NTs at the synapse 4) Produce important
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