TYPES OF NEUHOXS 



D!) 



Unipolar Cells. l)urin<i: the earl\' ditt'crentiation of the iieuro- 

 bhists, a uiiij)ohir coiulitioii develops when a siii(i;le i)rocess f^rows 

 out from the cell body. This condition does not usually remain 

 throua;hout development, for one or more additional processes are 

 developed from difi'erent portions of the cyton, and change the cell 

 into a bipolar or multipolar type when differentiation is complete. 

 In some lower \ertebrates the unipolar condition is believed to 



remain in com})letely differentiated 

 neurons of the brain, spinal cord, and 

 ganglia. In such cases there is some 

 uncertainty as to whether the single 

 grou]) of similar processes arising from 

 one region of the cell represents an 

 axon or dendrite, though in some in- 



FiG. 54. — Photograph of a 

 pyramidal cell from the cere- 

 bral cortex of a cat with two 

 protoplasmic astrocytes sur- 

 rounding the largest dendritic 

 process. The axon leaves the 

 base of the pyriform cell body. 



Fic;. 55. — A photograph of a 

 Purkinje cell from the cerebellum 

 of the cat, showing much branched 

 dendritic processes and a single fine 

 axon process. Golgi technique. 



stances both axons and dendrites may be differentiated from part 

 of the process. 



Bipolar Cells. — In these neurons a single axon and dendrite are 

 de\-el()pe(l and project from opposite ends of the cyton. This condi- 

 tion is found in the embryological development of the spinal and 

 cranial ganglion neurons before they are completely differentiated, 

 and is true of completel}' differentiated neurons found hi the retina 

 and parts of the ear. 



