= Spinal nerve
A <spinal nerve> is a paired peripheral <nerve> formed by the union of a sensory <dorsal root> and a motor <ventral root> near the <spinal cord>. Humans usually have 31 pairs. Because sensory and motor fibres travel together after the roots unite, a <spinal nerve> is mixed even though its two roots have different principal signaling directions.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 13.4, Spinal Nerves]{ref}
The resulting <spinal nerve> divides into posterior and anterior <spinal nerve rami>, both of which remain mixed. A <dorsal root> and a posterior ramus are therefore different structures: one joins the <spinal cord>, while the other distributes fibres after root union. Anterior <spinal nerve rami> can reorganize into a <nerve plexus>, so one named limb <nerve> can contain fibres from several spinal levels.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 13.4, Spinal Nerves and Nerve Plexuses]{ref}
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