副神经（accessory nerve）是第11对脑神经，编号XI。它又可分成颅根（Cranial root）和脊髓根（Spinal root）两条分支。其中颅根和迷走神经的分支伴行，走向咽喉。脊髓根则和数条颈神经分支合流，支配胸锁乳突肌以及斜方肌的运动。 颅根的纤维为特殊内脏运动纤维，起自疑核，自迷走神经根下方出脑后与脊髓根同行，经颈静脉孔出颅，加入迷走神经，支配咽喉肌。脊髓根的纤维为特殊内脏运动纤维，起自脊髓颈部的副神经脊髓核，由脊神经前后根之间出脊髓，在椎管内上行，经枕骨大孔入颅腔，与颅根汇合一 起出颅腔。出颅腔后，又与颅根分开，绕颈内静脉行向外下，经胸锁乳突肌深面继续向外下斜行进入斜方肌深面，分支支配此二肌。

The accessory nerve is a cranial nerve that controls the sternocleidomastoid and trapezius muscles. As part of it was formerly believed to originate in the brain, it is considered the eleventh of twelve cranial nerves, or simply cranial nerve XI.

Traditional descriptions of the accessory nerve divide it into two parts: a spinal part and a cranial part. However, because the cranial component rapidly joins the vagus nerve, becoming an integral part of said nerve, modern descriptions often consider the cranial component to be part of the vagus nerve and not part of the accessory nerve proper. For this reason, in contemporary discussions of the accessory nerve, the common practice is to dismiss the cranial part altogether, referring to the accessory nerve specifically as the spinal accessory nerve.