Corpus: Nucleus ambiguus

The ambiguous nucleus is a predominantly motor cranial nerve nucleus at the base of the rhomboid fossa of the medulla oblongata (brain stem), which consists of large motor neurones.

The nucleus ambiguus sends special visceromotor (branchiomotor) fibres to the:

• Glossopharyngeal nerve (IX nerve): Innervation of the muscles of the upper throat (pharynx)
• Vagus nerve (nerve X): Innervation of the muscles of the lower pharynx and upper oesophagus and larynx
• Accessory nerve (nerve XI, radix cranialis): innervation of the laryngeal muscles

In addition, preganglionic parasympathetic neurones for supplying the heart are located in the nucleus ambiguus.

The ambiguous nucleus receives afferent fibres from the nerve cells of the following regions:

• Motor cortex (cerebrum) via tractus corticobulbaris
• Nucleus solitarius
• Medial and lateral reticular formation
• Pons (bridge)
• Nucleus spinalis nervi trigemini

The motor neurones of the nucleus ambiguus are largely responsible for controlling speech and the act of swallowing. The parasympathetic neurones have a cardioinhibitory effect.

Lesions of the ambiguous nucleus lead to dysphagia and dysphonia as well as to ipsilateral paralysis of the soft palate with displacement of the uvula to the contralateral side, i.e. the side facing away from the damage (backdrop phenomenon).