| Neurons that have only one cytoplasmic process attached to the cell body are structurally classified as unipolar (or pseudounipolar). The cell body (= soma) of unipolar neurons sits aside the axon, and the two are connected by the cytoplasmic process. This arrangement makes it appear as if the cytoplasmic process splits the axon into two portions. A peripheral process carries action potentials (= impulses) to the cell body and a central process carries action potentials from the cell body into the the CNS. The peripheral process is usually long, often measuring over a meter in length. In contrast, the central process varies in length. For example, the central process of the touch neuron is much longer than the central process for the pain neuron. The dendrite(s) of unipolar neurons attach directly to the peripheral axon process. They are embedded in the peripheral organs and usually serve as receptors. In the skin, the receptors are often enclosed within a capsule.
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. |
