812 



THE NERVE SYSTEM 



have been best revealed by the methods of Ehrlich and Golgi. According to the number of 

 processes arising from the cell body, neurones are referred to as (1) unipolar, (2} bipolar, and 

 (3) multipolar nerve cells. 



1. Unipolar cells are met with frequently in early stages of embryonic development, but arc 

 rare in the adult, being found only in the retina, olfactory bulb, and within the baskets of the 

 I'lirkinjean cells of the cerebellum. They are called amacrine cells. The cells of the cerebro- 

 spinal ganglia (excepting the cochlear and vestibular) are apparently unipolar, but they are 

 developmentally and functionally of bipolar nature. 



2. Bipolar cells are found almost exclusively in the peripheral sensor systems, as in the 

 olfactory membrane, in the retina, in the cochlear and vestibular gamrlia. and in the cerebro- 

 spinal ganglia of the embryo. 



3. Multipolar cells are the most numerous and form the principal elements of nep:e. centres 

 throughout the system. They are termed multipolar because of the greater or less number of 

 dendrites given oft' in addition to the single axone. 1 



The terms "unipolar" and "multipolar" must be restricted to the morphological sense; 

 dynamically all nerve cells are bipolar. 



According to the relations of the axone we distinguish, after Golgi, two kinds of neurones: 



I. Neurones with long ax ones which become the axis cylinder of a central or peripheral nerve 

 fibre. The axones give off several collaterals which, like the parent stem, break into finely 

 branched terminals or telodendria. 



II. Neurones with relatively short axones which do not go into the formation of a nerve 

 fibre, but break up into terminal twigs in the vicinity of the cell-bodies from which they arise. 

 Type II is generally termed, for brevity's sake, the Golgi cell. 



FIG. 582. Purkinjean cell from human cerebellum, as seen in a 

 plane transverse to the long axis of a cerebellar folium, a. Axone. 

 clt. Collaterals. (Golgi method.) 



FIG. 583. Profile view of Purkin- 

 jean cell, in the plane of the long axis 

 of a cerebellar folium. 



According to the morphological relations of the dendrites, neurones are classified as follows: 



(a) Stellate cells, the dendrites of which spring at intervals from the whole circumference 

 of the cell body and pass toward all directions (motor cells in ventral horn and tract cells of the 

 cord). 



(b) Cells with one principal stout dendrite (among other lesser dendrites) which gives off side 

 branches and ends in fine terminal twigs (pyramidal cells of cerebral cortex; mitral cells of 

 olfactory bulb). 



(c) Arboriform cells, giving off branched dendrites from both base and apex, resembling the 

 roots and the branches of a tree; the axone often springs from the base of one of the root-like 

 dendrites (pyramidal cells of the hippocampus). 



1 Exceptionally, more than one axone has been observed arising from a single cell, as in the Cajal cells of the 

 cerebral cortex. 



