![]() ![]() They are characterized by Wallerian degeneration, a mechanical breakdown of the axon and ensheathing myelin (a specialization of Schwann-cell plasma membranes), of the portion of the nerve fiber distal to the disruption. ![]() Not surprisingly, such disturbances, known as axonopathies or neuropathies, are not rare. Any disruption of the cytoskeletal machinery or energy supply (oxygen, glucose, adenosine triphosphate, nicotinamide adenine dinucleotide, or mitochondria) required to keep axonal transport functional can thus cause distal axonal damage. Virtually all assembly of macromolecules and organelles occurs in the cell body, and items needed in the axons must travel these long distances (and sometimes back again) by axonal transport. The axons of a 100-μM-wide sensory neuron cell body can span the distance between the toes and the brain, nearly 2 meters in some humans (and longer in giraffes and whales). Peripheral nerves, made up of axons wrapped with Schwann cells (glial cells that provide electrical insulation), are the longest cells. Peripheral nerves form a massively parallel bidirectional network that transmits information from the outside world to the central nervous system (CNS) and then back to the rest of the body. ![]()
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