. The chordates. Chordata. Fig. 260 (Left). Diagram showing how an embryonic bipolar nerve cell is trans- formed into a unipolar cell ("T-cell") such as occurs in ganglions of the dorsal roots of spinal nerves. (Courtesy, Bremer: "Text-Book of Histology," Phila- delphia, The Blakiston Company.; Fig. 261 (Right). Nerve-cell, with processes cut short; from human spinal cord. (X 430.) (Courtesy, Bremer: "Text-Book of Histology," Philadelphia, The Blakiston Company.) receptor cell itself produces a nerve-fiber which conducts to the central organ—, an olfactory cel
. The chordates. Chordata. Fig. 260 (Left). Diagram showing how an embryonic bipolar nerve cell is trans- formed into a unipolar cell ("T-cell") such as occurs in ganglions of the dorsal roots of spinal nerves. (Courtesy, Bremer: "Text-Book of Histology," Phila- delphia, The Blakiston Company.; Fig. 261 (Right). Nerve-cell, with processes cut short; from human spinal cord. (X 430.) (Courtesy, Bremer: "Text-Book of Histology," Philadelphia, The Blakiston Company.) receptor cell itself produces a nerve-fiber which conducts to the central organ—, an olfactory cell and its fiber (Figs. 167, 249C). In such cases one neuron serves as both receptor and conductor. In other cases, as in the auditory organ and taste-buds (Figs. 167, 250), the epi- thelial receptors do not produce nerve-fibers, but are intimately related to the terminal twigs of afferent nerve-fibers whose cell-bodies lie in some deep ganglion such as the acoustic ganglion or a spinal ganglion. Nerve cells vary greatly in size, but in general are relatively large. They are often the largest cells in the body exclusive of eggs. Some possess two or more nuclei, and the bulky mass of cytoplasm, invested by a supporting membrane of connective tissue, may be penetrated by narrow canals serving for an intracellular circulation of lymph. The most striking characteristic of the body of a neuron is the presence of large masses of a granular substance which has a strong affinity for the aniline dye, methylene blue. These Nissl's bodies (Fig. 261) have been shown to become reduced in neurons which have been excessively active, indicating that the bodies contain something which is a source of energy for nervous activity. Less conspicuous are the neurofibrils (Fig. 259), extremely fine fibrils which ordinarily are seen only after use of special staining methods. Such neurofibrils may form an elaborate system within the body of the neuron and may be traced into the neuraxon and larger den
Size: 1934px × 1293px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollect, bookpublisherphiladelphiablakiston
