The Human Brain : From Neurone to Nervous System


  1. When axons are transected, the distal section dies, and the cell body begins synthesis of proteins necessary for axonal regeneration - regrowth; this is often succssful in the peripheral nervous system, but not in the central nervous system

  2. When an axon is transected, the terminal portion of the axon degenerates (Wallerian Degeneration), and the central end of the cut axon begins to regrow. The growing end of this regenerating axon is known as the growth cone.

  3. The metabolism of the neurone alters so that it synthesises structural proteins; the changes in the body of the neurone include marked changes to the Nissl substance, and are described as Chromatolysis.

  4. The growing sprouts of the axons may reconnect with their target organ. In skeletal muscle damage to alpha motoneurones can result in the sprouting of adjacent motoneurones and reinnervation of the denervated muscle fibres. In this instance the size of the motor unit is increased.

  5. In the CNS, such regeneration is rarely successful, and the loss of synaptic inputs can cause post-synaptic neurones to degenerate or atrophy or show functional changes.

  6. Adult neurones are largely incapable of mitosis. However there are a few sites in the CNS where new neurones can be produced from stem cells: these include the sub-ventricular zone (SVZ) of the hypothalamus, the hippocampus and cerebellum in most mammalian species

  7. Key Words: Wallerian Degeneration; Chromatolysis, Axonal sprouting, Neural Stem Cells.