Neurons can be divided into five categories. namely-
1. Apolar: A non-polar neuron has no protracted segment. Apolar neurons are located in the outer layer of the cerebral hemisphere and in the intermediate nuclear layer of the retina.
2. Unipolar: A unipolar neuron has an elongated segment. It is a sensor. The peripheral nervous system of vertebrates consists of unipolar neurons.
3. Bipolar: Bipolar neurons have two elongated parts. One is the axon and the other is the dendrite. These later transform into unipolar or multipolar neurons. In the human embryo, there are bipolar neurons in the retina, nose and cochlea.
4. Multipolar: Multipolar neurons have many elongated parts. The mammalian brain and spinal cord contain multipolar neurons.
5. Pseudopolar: Pseudopolar neuron has two pronged parts first. Later merge into one. It arises from bipolar neurons. Spinal ganglia and carotic ganglia contain pseudopolar neurons.