Figure 114

Photomicrograph of nerve cell bodies. This photomicrograph shows a region of the ventral (anterior) horn of a human spinal cord stained with toluidine blue. Typical features of the nerve cell bodies visible in this photomicrograph include large, spherical, pale-stained nuclei with a single prominent nucleolus and abundant Nissl bodies within the cytoplasm of the perikaryon. Most of the small nuclei belong to neuroglial cells. The remainder of the field consists of nerve fibers and cytoplasm of neuroglial cells. x640.

level of anabolic activity needed to' maintain these large cells.

Neurons do not divide; they must last for a lifetime

Although neurons do not replicate, the subcellular components of the neurons turn over regularly and have molecular lifespans measured in hours, days, and weeks. The constant need to replace enzymes, transmitter substances, membrane components, and other complex molecules explains the morphologic features characteristic of a high level of synthetic activity. Newly synthesized protein molecules are transported to distant locations within a neuron in a process referred to as axonal transport (page 293).

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