a cluster of primary sensory neurons forming a usually visible swelling in the course of a peripheral nerve or its posterior root; such nerve cells establish the sole afferent neural connection between the sensory periphery (skin, mucous membranes of the oral and nasal cavities, muscle tissue, tendons, joint capsules, special sense organs, blood vessel walls, and tissues of the internal organs) and the central nervous system; they are the cells of origin of all sensory fibers of the peripheral nervous system.