Axons ranges in size from 0.2 um to 20 um and can extend up to 1 meter. The axon arises from the axon hillock and extends towards the target cell where it divides into fine branches with specialized swellings. These swellings form the presynaptic terminals of cells. The synaptic cleft is a space that separates the presynaptic terminals from the postsynaptic cell . The other cells of the nervous system, Glial cells , can be divided into macroglia and microglia .
Microglia arise from macrophages and remove debris after cell injury or death.
Macroglia can be divided into schwann cells , oligodendrocytes and astrocytes . Schwann cells create the myelin sheath around axons in the peripheral nervous system. Oligodendrocytes produce the myelin in the central nervous system. Astrocytes contain many intermediate filaments suggesting they provide structural support . Both schwann cells and oligodendrocytes can enclose many unmyelinated axons.