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Nervous Tissue

Nervous Tissue. Graduate Microanatomy Spring 1999 Sandra H. Bolanos. Central Nervous System. Brain Spinal Cord. Brain. Cranium (brain case) Cortex Gray matter Nerve cell bodies Interior Portion White matter Axons Ventricles CSF. Spinal Cord.

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Nervous Tissue

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  1. Nervous Tissue Graduate Microanatomy Spring 1999 Sandra H. Bolanos

  2. Central Nervous System • Brain • Spinal Cord

  3. Brain • Cranium (brain case) • Cortex Gray matter Nerve cell bodies • Interior Portion White matter Axons Ventricles CSF

  4. Spinal Cord • Occupies two-thirds of the vertebral canal • Enveloped by meninges • Cervical and lumbar enlargements • Gray matter centrally located

  5. Meninges • 3 layers of connective tissue membranes • Surround and protect brain and spinal cord Pia Mater Arachnoid Dura Mater

  6. Peripheral Nervous System 31 pairs of spinal nerves 12 pairs of cranial nerves • Nerves that emerge from central nervous system:

  7. Sympathetic Parasympathetic Autonomic Nervous System

  8. Cellular Composition of CNS • Neurons and their processes • Support cells: Astrocytes Oligodendrocytes Ependymal cells Microglia

  9. Astrocytes • In developing NS, form structural framework to guide migration of developing neurons • In developed NS, form • structural scaffolding for • more specialized neural • elements • Clear ECM of by-products • of neural activity and • contain glycogen reserves • Extend foot processes around • blood capillaries

  10. Blood Brain Barrier • Capillaries of the CNS not fenestrated and have intercellular tight junctions between endothelial cells • Highly resistant to passage of ions or small molecules • Do not exhibit transendothelial transport in small vesicles • Astrocytes may influence capillaries to express these unique properties

  11. Oligodendrocytes • Produce myelin within CNS • Each cell sends out several processes and myelinates several nearby axons

  12. Ependymal Cells • Epithelial-like • Ciliated • Line cavities of brain ventricles and central canal of spinal cord forming sheets of cuboidal cells in contact with CSF

  13. Microglia • Specialized macrophages • In areas of injury, proliferate and become actively phagocytic in clearing cellular debris and ingesting damaged myelin

  14. Composition of PNS • Ganglia - a peripheral collection of nerve cell bodies together with efferent and afferent axons and support cells • Nerves - a collection of axons linked together by support tissue into an anatomically defined trunk

  15. Ganglia • Sensory (spinal sensory ganglia) • Non-sensory (sympathetic or parasympathetic) • Dorsal root ganglia, cranial ganglia, autonomic ganglia • Neuron cell bodies, support cells, loose fibrocollagenous tissue

  16. Nerves • Motor Innervate skeletal muscle (CNS) Innervate smooth muscle (PNS) • Sensory • Myelinated or Non-myelinated • Axons, Schwann cells, fibroblast cells, blood vessels

  17. - 3 types of support tissue in a nerve trunk: • Endoneurium Surrounds individual axons, their associated Schwann cells, and capillary blood vessels • Perineurium Surrounds groups of axons and endoneurium to form fascicles • Epineurium binds individual nerve fascicles into a nerve trunk

  18. Endoneurium Collagen fibers that are longitudinally oriented ECM rich in GAGs and sparse fibroblasts • Perineurium 7-8 concentric layers of epithelium-like flattened cells separated by layers of collagen and joined by junctional complexes Each layer of cells surrounded by an external lamina • Epineurium Outer sheath of loose fibrocollagenous tissue May also include adipose tissue and muscular artery that supplies the nerve trunk Epi Peri Fascicle Endo

  19. Schwann Cells • PNS • Myelinate only one axon

  20. Neurons • Gather information from sensory receptors • Process information and provide a memory • Generate appropriate signals to effector cells • Cell body, dendrites, axon, and synaptic bouton

  21. Cell Body • Pale-staining • Conspicuous nucleolus • Little heterochromatin • Nissl bodies • Golgi complex • Mitochondria • Lysosomes • Neurofilaments • Microfilaments • Microtubules

  22. Dendrites • Radiating processes of the cell body • Receive signals (synapses) from other neurons • Broader than axons • Extensive branching increases cell surface available for receiving signals from other neurons • Organelles similar to those of the perikaryon (no Golgi bodies) • As distance from cell body increases, smooth ER and NFs reduced but MTs and mitochondria still prominent

  23. Axons • A single long process capable of generating a nerve impulse • More slender and usually longer than dendrites • Branch at right angles • Can be quite long (spinal motor neurons that supply foot muscles 40 inches in length) • Axon Hillock is conical extension of cell body from which axon arises • Axoplasm lacks Nissl bodies

  24. Branches as it approaches its end forming small expansions • Terminal boutons contact other cells to form a synapse • At synapse, chemicals or electrical signals pass from one neuron to another cell known as the effector cell • Neurotransmitters act rapidly and locally to activate their target cells and neuromodulators that regulate these events

  25. Neuron Shapes

  26. Neuron Types

  27. Myelin • Insulation minimizes leakage of current from membrane speeds up conduction along axons • Reduction of electrical capacitance wide axons lower capacitance than narrow ones increases diameter of axons increases speed of nerve conduction • Myelin-producing cells Oligodendrocytes (CNS) Schwann cells (PNS) • Nodes of Ranvier space between each unit of myelin increase efficiency of nerve conduction

  28. Myelin

  29. Synapses • Specialized region of contact where NT released from axon to stimulate another cell

  30. Axonal Transport • Anterograde or retrograde • Fast or slow • Microtubules • Motor proteins • Ca2+ • ATP Minus end Plus end Kinesin Dynein

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