Neurons (= nerve cells) are the functional units of the nervous system. Even though they vary in size and shape, most have structural characteristics similar to the spinal cord neuron shown to left. Neurons have at their core an expanded area of cytoplasm called the cell body (= soma or perikaryon). It surrounds the nucleus and contains the organelles that perform many of the cell's supportive metabolic functions. A single, branched axon extends from one side of the cell body. This elongated cytoplasmic process transports action potentials (= electro-chemical impulses) away from the cell body (= conduction) and releases neurotransmitter from its bulbous ends (= secretion). Also attached to the cell body are several branched dendrites. The dendritic processes form part of the receptive zone of the neuron, and changes in the environment causes them to send weak electo-chemical signals toward the cell body and axon (= excitability or irritability). Many neurons do not have the same structural characteristics just described. Instead, they may have ..... a. dendrites and an axon that do not directly attached to the cell body. b. dendrites that attach directly to the axon. c. only one dendrite.