Nerve Cells

Nerve cells, being complete animal cells, consist of cytoplasm with nucleus, nucleolus, and centrosome. The cytoplasm is of special interest on account of : (a) its peculiar structure; (b) certain differentiated masses in its interior.

(a) Running through the cytoplasm are many minute fibrils (neurofibrillae) which are continuous with fibrils in the cell processes, indicating thus probable definite paths for the passage of impulses through the cell (Fig. 8).

(b) Embedded in the cytoplasm are small masses of granular material which stain deeply with aniline dyes. They are known as Nissl's granules or tigroid bodies, and consist of chromophilic material. They undergo alterations in constitution and distribution during the activity of the cell. The cytoplasm also contains, in the vicinity of the nucleus, a certain amount of a yellowishbrown pigment (Fig. 7).

Nerve cells vary much in shape, and in many cases the form of the cell is characteristic of the region of the nervous system to which it belongs; to a limited extent, therefore, it is also indicative of its function. According to their general shape, nerve cells may be divided into two classes: (A) Bipolar cells; (B) Multipolar cells; but the latter class is usually further divided into (a) cells of type I; (b) cells of type II.