Page 225 - Biology_F5
P. 225

Biology for Advanced Level Secondary Schools

           Motor neurones (Efferent neurones)         effector organs such as muscles or glands,
           Motor neurones have short dendrites and  which eventually respond to the stimulus
           long axons; their dendrites and cell bodies  (Figure 4.5).  Axon always transmits
           are located in the CNS; and the axon is  impulses away from the cell body while
           outside the CNS. Motor neurones transmit  dendron carries impulses towards the cell
           nerve impulses from the CNS to the  body.
          FOR ONLINE READING ONLY

                Nucleus
                                 Cell body









             Dendrite                                Axon




                       Myelin sheath  Direction of nerve impulse







                                                    Node of Ranvier

                                    Figure 4.5: Structure of a motor neurone



           Classification of neurones based on the  neurones are sensory neurones that have
           number of dendrites                        two processes coming from the cell body;

           Neurones  can  also  be  classified  on  the  one dendron and one axon. Bipolar sensory
           basis of the  number  of their  dendrites  neurones are found in the retina of the eye,
           arising  from  the  soma  (cell  body).  In  ganglia  of the vestibulocochlear  nerve
           this  classification,  there  are  three  main  and the olfactory epithelium.  Multipolar
           types of neurones. These include unipolar  neurones  have  three  or more  processes
           neurone,  bipolar  neurone  and  multipolar  coming from the cell body. They possess
           neurone. Unipolar neurones have a single  one  axon  and  two  or more  dendrites.
           short dendrite terminating onto bush-like  Multipolar neurones form the major part
           tufts or dendrites. These are found in the  of the CNS. They include interneurones
           granular layer of the cerebellum. Bipolar  and motor neurones. (Figure 4.6).







                                                                      Form Five Student’s Book
            218
   220   221   222   223   224   225   226   227   228   229   230