The majority of cells in the nervous system are glial cells. During de velopment, these cells provide growth factors that stimulate the proli feration, migration and survival of neurones and their precursors, and promote and guide axonal growth. In the mature nervous system, glial cells provide insulating myelin sheath around axons and provide metabo lic and structural support for neurones. Glial cells also have a major influence on the local response to injury of central nerve tracts and the peripheral nervous system, either promoting, or inhibiting, axona l regrowth and recovery of lost...