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Fundamentals of the Nervous System and Nervous Tissue

PART 2. Fundamentals of the Nervous System and Nervous Tissue. Classification of Neurons. Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons Found in some special sensory organs

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Fundamentals of the Nervous System and Nervous Tissue

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  1. PART 2 Fundamentals of theNervous System andNervous Tissue

  2. Classification of Neurons • Structural classification • Multipolar – possess more than two processes • Numerous dendrites and one axon • Bipolar – possess two processes • Rare neurons • Found in some special sensory organs • Unipolar (pseudounipolar) – possess one short, single process • Start as bipolar neurons during development

  3. Neurons Classified by Structure Figure 12.10a

  4. Neurons Classified by Structure Figure 12.10b

  5. Neurons Classified by Structure Figure 12.10c

  6. Functional Classification of Neurons • Functional classification is • According to the direction the nerve impulse travels • Sensory (afferent) neurons

  7. Functional Classification of Neurons • Transmit impulses toward the CNS • Virtually all are unipolar neurons • Cell bodies in ganglia outside the CNS • Short, single process divides into • The central process – runs centrally into the CNS • The peripheral process – extends peripherally to the receptors

  8. Functional Classification of Neurons • Motor (efferent) neurons • Carry impulses away from the CNS to effector organs • Most motor neurons are multipolar • Cell bodies are within the CNS • Form junctions with effector cells • Interneurons (association neurons) – most are multipolar • Lie between motor and sensory neurons • Confined to the CNS

  9. Neurons Classified by Function Figure 12.11

  10. Supporting Cells • Six types of supporting cells • Four in the CNS • Two in the PNS • Provide supportive functions for neurons • Cover nonsynaptic regions of the neurons

  11. Neuroglial in the CNS • Neuroglia • Glial cells have branching processes and a central cell body • Outnumber neurons 10 to 1 • Make up half the mass of the brain • Can divide throughout life

  12. Neuroglia in the CNS • Astrocytes are the most abundant glial cell type • Sense when neurons release glutamate • Extract blood sugar from capillaries for energy • Take up and release ions in order to control environment around neurons • Involved in synapse formation in developing neural tissue • Produce molecules necessary for neuronal growth (BDTF) • Propagate calcium signals involved with memory

  13. Neuroglia in the CNS Figure 12.12a

  14. Neuroglia in the CNS • Microglia – smallest and least abundant glial cell • Phagocytes – the macrophages of the CNS • Engulf invading microorganisms and dead neurons • Derive from blood cells called monocytes Figure 12.12b

  15. Neuroglia in the CNS • Ependymal cells • Line the central cavity of the spinal cord and brain • Bear cilia – help circulate the cerebrospinal fluid • Oligodendrocytes – have few branches • Wrap their cell processes around axons in CNS • Produce myelin sheaths

  16. Neuroglia in the CNS Figure 12.12c, d

  17. Neuroglia in the PNS • Satellite cells – surround neuron cell bodies within ganglia • Schwann cells (neurolemmocytes) – surround axons in the PNS • Form myelin sheath around axons of the PNS Figure 12.13

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