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Biology for Advanced Level Secondary Schools

           nervous system comprises the cranial and  Types of neuroglia
           spinal nerves, which are packed together    Task 4.1
           with their  motor and sensory endings.      Search for information  from internet
           The  nervous  tissue  is the  main  tissue   sources and the library on neuroglia.
           component of the nervous system and it      Note  their  categories  and  specific
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           consists of closely packed nerve cells or   functions in the nervous system.
           neurones  with  very  small  intercellular   There  are  six types of neuroglia,  four
           spaces. Nervous tissue contains two types   of which are found in the CNS and two
           of cells, namely neurones and neuroglia.  in  the  PNS.  The  neuroglia  found in  the
           Neurones are specialised nerve cells that   CNS include astrocytes, microglia  cells,
           generate  and  conduct  nerve  impulses.   ependymal  cells  and oligodendrocytes,
           Neuroglia are non-neuronal cells which     while those found in PNS include satellite
                                                      cells and Schwann cells (Figure 4.1 a to f).
           assist in propagation of the nerve impulses   The collection of glia cells residing within

           and provision of nutrients to the neurones.  the walls of intestinal tract, beginning in
           Neuroglia also serve as supporting cells   the  oesophagus and extending  down to
           that  provide  electrical  insulation  and   the anus are known as enteric glia. The six
                                                      types of neuroglia are explained below:
           remove  debris. Cells of the neuroglia
           produce myelin sheath that increases the   (a) Microglia cell
           speed of impulses along the axon of the    These are the smallest neuroglia cells
           neuronal  fibres  and  offers  protection for   (Figure 4.1a). They are macrophage cells
           the axon.                                  that make up the primary immune system
                                                      for the CNS. These phagocytic cells help
                                                      to remove bacteria and waste (cleaning
                                                      neuronal debris).











                          (a)                    (b)                  (c)









                                 (d)                      (e)              (f)


            Figure 4.1:  Types of neuroglia (a) microglia (b) astrocytes (c) oligodendrocytes (d) ependymal
                                       (e) schwann and (f) satellite cells

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