The fast track system is an energy-dependent, active transport system. The fast track system can operate in reverse so that things like target cell messenger molecules can be transported from the axon terminals back to the cell body. The impulses are transmitted in one direction only, and are transmitted indirectly by chemical neurotransmitters stored in synaptic vesicles in the presynaptic terminal. The neurotransmitters include GABA, acetylcholine and noradrenaline and when a nerve impulse arises at a presynaptic terminal, they are released by exocytosis into the synaptic cleft. If the nerve impulse continues, the released chemicals depolarise the postsynaptic membrane.
Bipolar neurons have one axon and one dendrite at opposite poles of a rounded body.
Pseudounipolar neurons have a single short process attached to a rounded cell body. The single process quickly divides into two. Impulses from the periphery can bypass the cell body. Pseudounipolar neurons are typical of dorsal root ganglia. Multipolar neurons typically have a pyramidal or polygonal cell body, numerous dendrites and a single axon.