Development of Myelination and Axon Ensheathment

Another type of cell, which is derived from both the neural crest and the wall of the neural tube and which participates in covering the neurons of the PNS, is the satellite cell. Satellite cells completely encapsulate the cell bodies of sensory neurons in the sensory ganglia of both the cranial and spinal nerves, and also the postganglionic neurons of the sympathetic and parasympathetic ganglia. Finally, there is a specialized glial cell that shares properties of Schwann and satellite cells but is only found apposed to the unmyelinated axons of the olfactory nerve; these axons originate from receptor neurons in the nose that are continually replaced throughout life and thus must regrow into the olfactory bulb in the CNS and make new synapses. These olfactory ensheathing cells are apparently specialized to support the constant regrowth of the axons and the establishment of new connections in the CNS. Accordingly, there is great interest in these cells as a substrate for improved axon growth in other regions of the CNS after injury.

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