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Unit IV NERVOUS SYSTEM HISTOLOGY

Biology 220 Anatomy & Physiology. Unit IV NERVOUS SYSTEM HISTOLOGY. Chapter 11 pp. 387-396. E. Gorski/ E. Lathrop-Davis/ S. Kabrhel. Functions. Sensory – recognize changes in environment [stimuli] Integration – analysis of sensory information, storage of information, decisions

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Unit IV NERVOUS SYSTEM HISTOLOGY

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  1. Biology 220 Anatomy & Physiology Unit IVNERVOUS SYSTEM HISTOLOGY Chapter 11 pp. 387-396 E. Gorski/ E. Lathrop-Davis/ S. Kabrhel

  2. Functions • Sensory – recognize changes in environment [stimuli] • Integration – analysis of sensory information, storage of information, decisions • Motor – initiates impulses to effectors [muscles or glands] that do work)

  3. Organization Fig. 11.2, p. 388

  4. Cells Neurons and Supporting Cells • neurons • produce impulses to transfer information • amitotic (mostly), high metabolic rates, long-lived • supporting cells – support, protect, nurture neurons • neuroglia (glial cells) • astrocytes, oligodendrocytes, ependymocytes, microglia, satellite cells, Schwann cells (neurolemmocytes) • in CNS, tumors arise from abnormal divisions of glial cells

  5. Supporting Cells in the CNS • Astrocytes – connect neurons to blood supply • Microglia – phagocytic Fig. 11.3, p. 389

  6. Supporting Cells in the CNS • Oligodendrocytes – produce myelin sheath • Ependymal cells – epithelial lining of brain ventricles and central canal of spinal cord • produce cerebrospinal fluid Fig. 11.3, p. 389

  7. Supporting Cells in PNS • Satellite cells –surround neuron cell bodies in ganglia • Schwann cells (neurolemmocytes) • form myelin sheaths around larger nerve fibers • play role in regeneration of nerve fibers Fig. 11.3, p. 389

  8. Myelination (Myelin Sheath) • formed by oligodendrocytes (CNS), Schwann cells (PNS) • surrounds some axons (fibers) in CNS and PNS • composed of lipids and proteins (neurolemma = cell membrane of Schwann cell in PNS) • nodes of Ranvier = spaces between sheath cells • importance of myelin sheath: • increase speed of impulse conduction • decrease energy required (Na+/K+ pump only active at nodes) Multiple sclerosis– destruction of myelin sheath in CNS  diminishes impulse conduction

  9. Development of Myelin Sheath Fig. 11.5, p. 393

  10. Neurons General: • most are amitotic (no cell division) • communicate with each other at synapses • neuron-neuron • neuroeffector junction (NEJ) • neuromuscular junction (NMJ) • neuroglandular junction (NGJ) • high rate of aerobic respiration

  11. Neuron Cell body (perikaryon) • contains nucleus • rich in ribosomes & rough ER (Nissl bodies) • produces proteins for export to axon or dendrite • lots of mitochondria • neurofibrils

  12. Neuron Processes Dendrites (d) • bring depolarization toward cell body • no myelin Axons (a) • generally take action potential (impulse) away form cell body • myelinated or unmyelinated • axon hillock • telodendria • synaptic end bulb d Fig. 11.4, p. a

  13. Classification of Neurons • Based on structure – number of processes extending from cell body • unipolar • bipolar • multipolar • Based on function – type & direction of information • sensory • motor • association (interneurons)

  14. Major Structural Classes Unipolar neurons • Unipolar neurons • dendrites short, lead to myelinated axon (central and peripheral processes) before cell body • generally sensory neurons within peripheral nervous system Table 11.1, p. 395

  15. Major Structural Classes Bipolar Neurons • Bipolar neurons • one axon, one dendrite • sensory, including retina of eye and olfactory mucosa Table 11.1, p. 395

  16. Major Structural Classes Multipolar Neurons • Multipolar : • one axon, several dendrites • interneurons, motor neurons • may be myelinated or unmyelinated Table 11.1, p. 395

  17. Functional Classes of Neurons Based on type and direction of information (impulse) transmission • Sensory: • afferent (brings sensory info to CNS) • most unipolar or bipolar • Interneurons: • integration between sensory & motor in CNS • most multipolar • Motor: • efferent (goes toward/to effector) • most multipolar

  18. Other Definitions • Nerve fiber:long axon (primarily in PNS) • Nerve:bundle of neuron processes (fibers) in PNS • Tract:bundle of neuron processes in CNS • Ganglion (ganglia): cluster of cell bodies in PNS • Nucleus (nuclei): cluster of cell bodies in CNS • White matter: myelinated nerve processes in CNS • outside in spinal cord; inside in brain • Gray matter: unmyelinated nerve processes in CNS • inside in spinal cord, outside in brain

  19. Nerve Structure • Nerves = bundles of neuron processes (axons) in PNS • Coverings: • endoneurium: wraps individual fibers (over myelin sheath); composed of areolar CT • perineurium: groups fibers into bundles called fascicles; composed of dense irregular CT • epineurium: encloses fascicles, arteries, veins; composed of dense irregular connective tissue Fig. 13.2, p. 481

  20. Peripheral Nerve Types • Sensorynerves carry afferent fibers only • Motornerves carry efferent fibers only • Mixednerves carry both kinds of fibers 1 = epineurium 2 = perineurium 3 = endoneurium

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