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Neurons are structurally classified based on the number of processes that attach to the cell body (soma).
Unipolar (pseudounipolar) neurons have one process that atttaches to the cell body. This short process also attaches to the axon, which makes it appear as if the cell body sits aside the axon.
Inside the cell body are the nucleus and typical organelles. The secretory vesicles and macromolecules made in the cell body enter the nearby axon via the interconnecting process.
The location of the cell body process appears to divide the axon into two parts, a peripheral process and a central process.
At the distal end of the peripheral process are dendrites, which are usually embedded in a peripheral organ and function as a receptor.
The peripheral process conducts action potentials from the dendrites to the cell body, where they pass directly to the central process. They then move away from the cell body and enter the central nervous system (CNS).
Peripheral processes are usually long. In the lower extremities, they can be over a meter in length.
In comparison, central processes vary in length. Some stop after entering the CNS and synapse with another neuron. Others enter the CNS and extend for some distance before synapsing.
Unipolar neurons are the most common type of sensory neuron. In addition to pain and touch, they also carry information about temperature, taste, proprioception (body position), and visceral organ activity.
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