NEURONS AND NEURON-CHAINS 



45 



detail in another chapter, are devoid of dendrites. The axon of such a unipolar 

 cell divides dichotomously into a central and a peripheral branch, each possess- 

 ing the characteristics of an axon. 



It is not uncommon to regard the peripheral branch of a sensory neuron as a dendrite, 

 because like the dendrites it conducts nerve impulses toward the cell body. But, since it 

 possesses all the morphologic characteristics of an axon, and since any axon is able to con- 

 duct nerve impulses throughout its length in either direction, and since these peripheral 

 branches of the sensory neurons actually convey impulses distally in the phenomenon of 



Fig. 24. Neurons with short axons (Type II of Golgi) from the cerebral cortex of a child: a, 



Axon. Golgi method. (Cajal.) 



antidromic conduction (Bayliss, General Physiology, p. 474), it seems best to consider both 

 central and peripheral branches as divisions of a common axonic stem. (See Barker, The 

 Nervous System, p. 361.) 



From what has been said it will be apparent that a neuron usually possesses 

 several dendrites and a single axon, but some have only one process, which is 

 then an axon. It may be added that some neurons have more than one axon. 



Nerve-fibers are axons naked or insheathed. Two myelinated peripheral 

 nerve-fibers are shown in Fig. 26. The axon or axis-cylinder is composed of 



