The neuron can be generally divided into three main functional parts, the cell body, the axon, and the dendrites. The cell body is the biosynthetic center of the cell. This is where cellular metabolism occurs, as well as the production of proteins and membrane. Some people believe that this production machinery , consisting of free ribosomes and rough endoplasmic reticulum (rER), is probably the most active and best developed of any cell in the body. The ribosomes and rER are the cellular organelles responsible for protein production and packaging. The dendrites are responsible for recieving signals and conducting them up the cell to the cell body and on to the axon. The axon is the portion of the neuron that is responsable for the passing of the cellular message from the, neuron to either other neurons, or neural receptors. Bundles of these processes, axons and dendrites so called because they extend outward from the cell body, are called tracts in the CNS(this stands for central nervous system and consists of the brain and spinal column), and nerves in the PNS (this stands for peripheral nervous system and it represents all other nerves outside of the CNS).

The cell body contains all of the basic cellular organelles of most other cells but is conspicuously lacking centrioles. Centrioles are organelles (the cellular equivalent of human organs) that are responsible for the formation of the mitiotic spindle, which is important for cellular replication. The rER is very well developed and often referred to as Nissl bodies or Chromaticphilic substance because it stains darkly with basic dyes. The cell body contains intermediate filaments called neurofibrils, which are important in intracelluar transport and maintaing cell shape and integrity. Bundles of these neurofibrils are called neurofilaments. Aging neurons are abundant with a pigment called lipofuscin. This pigment accumulation is a harmless by-product of certain cellular functions. Most cell bodies are clustered within the CNS, in groups called nuclei. Fewer groupings of cell bodies are found outside of the protection of the CNS in the PNS. These clusters are called ganglia.

Dendrites are the part of the cell that recieve signals and conduct those signals to the rest of the neuron. These electrical signals are not nerve impulses but are short distance signals called graded potentials, or receptor potentials. Motor neurons can have hundreds of dendrites. This is a large amount of surface area dedicated to signal and impulse reception, hinting that a substantial stimulation is required before an action potential can be generated. Dendrites contain most organelles present in the cell body.

Neurons can have no more than a single axon (certain neurons in the CNS don't have any), responsible for the passing of messages from the neuron to other nerve cells or their effectors, targets of nerve impulses such as muscles. This where the actual nerve impulse, or action potential, occurs, on the axon. Axons can be very long, or very short in length. Some axons are 3-4 feet in length, extending from the middle of the spine to the bottom of the feet. Long axons are sometimes called nerve fibers. Just as axonal length may vary so too does the diameter of the axon. The larger the diameter, the thicker the axon, the faster it delivers nerve impulses. The region of the axon that attaches to the cell body is called the axon hillock. It is at this junction that action potentials are generated. The axon hillock is where the numerous graded potentials are summed, and thus the site for determination of whether threshold has been met. From here the axon extends a distance until it terminates into what is known as the secretory component of the neuron. The secretory component is the actual part of the neuron that transmits the nerve impulse on to the next neuron, and is the place in which synaptic potentials occur. This will be dealt with in a later section. The conducting component of the neuron lies between the axon hillock and the secretory component, consisting entirely of a length of axon. It is responsable for the propagation of nerve impulses away from the cell body. The conducting component sometimes branches into what are called axon collaterals. Though some axons may remain unbranched along their length, nearing their end, they usually branch into many (sometimes in excess of 10,000) smaller end branches called telodendria. The telodendria endings are variously called axonal terminals, synaptic knobs, or boutons, and are all part of the secretory component of the cell. Axons contain the same organelles as the cell body, except they lack Nissl bodies, so are dependent on the cell body to supply them with proteins and membrane components. Because of this transport mechanisms in the neuron are extremely important for transporting needed materials along the axon, and waste products from the axon. One of the most effective transporter mechanisms involves the use of kinesin, an ATP driven "carrier" protein that transports materials from one part of a cell to another.

As with most things there are multiple ways to classify neurons. The two most obvious ways are by structure and function. It is important to note that with neurons, as well as most biological entities, function follows form (structure). This means that the structure of a cell is the way it is because after millions of years of evolution that particular structure facilitates a specific function. This will become more evident as knowledge increases, and it is important to understand the connection between a neuron's form and it's particular function.

Structurally neurons can be classified as multipolar, bipolar or unipolar. Multipolar neurons have three or more processes and are the most common type in the CNS. Usually this means that there are numerous dendritic branches and one axonal process, but some neurons completely lack the axon and have only dendrites. Bipolar neurons have just two processes, an axon and a dendrite. These neurons are rare in adults, but when found are usually acting as receptor cells in some of the sense organs such as the eyes or nose. Unipolar neurons have a single process, which is very short, and almost always immediately divides into proximal and distal fibers, which head in different directions. The distal fiber is often associated with a sensory receptor and is sometimes referred to as the peripheral process. The proximal fiber, or central process, is generally associated with the CNS and is considered an axon as it has an action potential and is the "sender" of a neural message. The peripheral process is somewhat of an enigma however. It acts like an axon in that it has an action potential, is normally myelinated when large, has a uniform diameter, and is indistinguishable from an axon microscopically. However it also acts as a dendrite in that it conducts message a toward the cell body of the neuron. We choose to think of it as an axon, and the actual receptor ends of it as miniature dendrites that skip the cell body and go straight on to the axon.

Neurons can also be functionally classified as either sensory (or afferent) neurons, motor (or efferent) neurons, or association (or inter) neurons. This classification scheme is largely based on the direction of the nerve impulse. Sensory neurons conduct messages from sensory receptors toward the CNS and are usually always unipolar. Motor neurons are almost always multipolar and conduct impulses away from the CNS. All motor neurons form junctions with their effector cells. Between the sensory and motor neurons lie the interneurons. These cells are typically multipolar and confined to the CNS.