Expansion
Unipolar, bipolar and multipolar, with Nissl substance in the cell body
Expansion
Structure
- Cell body (perikaryon): contains the nucleus and Nissl substance, which is stacked rough endoplasmic reticulum staining basophilic
- Dendrites: receive input; contain Nissl substance
- Axon hillock and axon: no Nissl substance, which distinguishes them histologically. The hillock is the site of action potential initiation
- Synaptic terminals
Classification by processes
- Multipolar: most neurones, including motor neurones
- Bipolar: retina, olfactory epithelium, vestibulocochlear ganglia
- Pseudounipolar: dorsal root ganglion sensory neurones, where a single process divides into peripheral and central branches
Chromatolysis is the response to axonal injury: the cell body swells, the nucleus moves peripherally and Nissl substance disperses, reflecting a shift from neurotransmitter production to structural repair. It is a useful histological marker of recent axonal injury.
Neurones are permanent cells, unable to divide, which is why CNS injury heals by gliosis rather than regeneration, and why neurogenesis in the adult is limited to a few sites such as the hippocampal dentate gyrus.