The nucleus ambiguus (literally "ambiguous nucleus") is a region of histologically disparate cells located just dorsal (posterior) to the inferior olivary nucleus in the lateral portion of the upper (rostral) medulla.
This nucleus gives rise to the efferent motor fibers of the vagus nerve (CN X) terminating in the laryngeal and pharyngeal muscles, as well as to the efferent motor fibers of the glossopharyngeal nerve (CN IX) terminating in the stylopharyngeus.
The muscles supplied by the vagus (included with this is the cranial part of the accessory nerve), such as levator veli palatini, are also necessary to swallow properly through integration by the nucleus of the solitary tract. The vagus also supplies the upper part of the esophagus, and other parts of the pharynx and larynx.
As well as motor functions, nucleus ambiguus also contains the preganglionic neurons for the heart.