Most neurons found in the human body are multipolar, meaning they have more than two cell processes with only one being an axon and the remaining processes being dendrites. Bipolar neurons of the retina or olfactory mucosa have one dendritic process and an axon coming off the cell body. Pseudounipolar neurons found in the spinal cord ganglia enable sensory impluses picked up by the dendrites to travel directly to the axon without passing through the cell body. Neurons may also be classified according to function. Sensory neurons are involved in the reception and transmission of sensory stimuli.
Motor neurons send inpulses to control muscles and glands.
Other neurons, interneurons, act as go-betweens between neurons as part of functional networks. Synapses are specialized functional cell junctions to propogate cellular signals. Most synapses are chemical synapses where vesicles in the presynaptic terminal contian a chemical messenger that is released to the synapic cleft when the presynaptic membrane is stimulated. The chemical messenger diffuses across the synaptic cleft to bind to receptors in the postsynaptic membrane. This induces a change in the polarization state of the postsynaptic membrane effecting cellular action.