Some types of neurons, such as Purkinje cells of the cerebellum, do not contain pigment granules. Neurons in the central nervous system have a variety of shapes. Neurons in the peripheral ganglia are surrounded by satellite cells forming a capsule around the neuron. The cell body of a neuron is its trophic center. Separation of a process from the cell body results in the death of that process.
Neuronal processes are extensions of the cell body and serve to initiate or conduct nerve impulses.
Dendrites generally receive and then conduct impulses toward the cell body, whereas axons conduct them away from the cell body. In unipolar neurons, in which the single process bifurcates into a peripheral and a central branch, both branches are structurally axon-like. In bipolar neurons, the effector and receptor portions of the neuron are found at the extreme ends of the two processes, and the entire intermediate portion is conductive. It is estimated that some neurons receive as many as 100,000 axon terminals on their dendritic expansion. The region of origin of the axon from a nerve cell is termed the axon hillock and is devoid of Nissl substance.