| Nucleus ambiguus | |
|---|---|
 Transverse section ofmedulla oblongata below the middle of the olive. ("Nucleus ambiguus" labeled at center right.) | |
| Details | |
| Identifiers | |
| Latin | nucleus ambiguus |
| NeuroNames | 765 |
| NeuroLex ID | birnlex_2650 |
| TA98 | A14.1.04.253 |
| TA2 | 6011 |
| FMA | 54588 |
| Anatomical terms of neuroanatomy | |
Thenucleus ambiguus ("ambiguous nucleus" in English) is a group of largemotor neurons, situated deep in themedullary part of thereticular formation named byJacob Clarke.[1] The nucleus ambiguus contains the cell bodies of neurons that innervate the muscles of thesoft palate,pharynx, andlarynx which are associated withspeech andswallowing. As well as motor neurons, the nucleus ambiguus contains preganglionic parasympathetic neurons which innervate postganglionic parasympathetic neurons in theheart.[2]
It is a region ofhistologically disparatecells located justdorsal (posterior) to theinferior olivary nucleus in thelateral portion of the upper (rostral)medulla. It receivesupper motor neuron innervation directly via thecorticobulbar tract.
This nucleus gives rise to the branchialefferent motor fibers of thevagus nerve (CN X) terminating in thelaryngeal,pharyngeal muscles, andmusculus uvulae;[3] as well as to the efferent motor fibers of theglossopharyngeal nerve (CN IX) terminating in thestylopharyngeus muscle. In addition, it gives efferent fibers to the cranial part of accessory nerve (CNXI).
The nucleus ambiguus controls the motor innervation of ipsilateral muscles of the soft palate, pharynx, larynx, and upper esophagus. Lesions of nucleus ambiguus result in nasal speech,dysphagia,dysphonia, and deviation of theuvula toward the contralateral side. Preganglionic parasympathetic to the heart also flow through the external formation of the nucleus.
The muscles supplied by thevagus (included with this is the cranial root of the accessory nerve), such aslevator veli palatini, are also necessary to swallow properly through integration by the nucleus of thesolitary tract. The vagus also supplies the upper part of theesophagus, and other parts of thepharynx andlarynx.
As well as motor neurons, the nucleus ambiguus in its "external formation" contains cholinergic preganglionic parasympathetic neurons for theheart.[2] These neurons are cardioinhibitory.[4] This cardioinhibitory effect is one of the means by which quick changes inblood pressure are achieved by the central nervous system (the primary means being changes in sympathetic nervous system activity, which constricts arterioles and makes the heart pump faster and harder). That is, through an integrated and antagonistic system withsympathetic outflow from thevasomotor center of the brainstem, the parasympathetic outflow arising from the nucleus ambiguus anddorsal motor nucleus of the vagus nerve acts to decrease cardiac activity in response to fast increases in blood pressure. The external formation of the nucleus ambiguus also sends bronchoconstrictor fibers to the bronchopulmonary system, which can produce reflexive decreases in pulmonary bronchial airflow. The pathophysiologic relevance of this system, which may act in concert with the cardioinhibitory system, is poorly understood, but likely plays a role in bronchospastic diseases likeCOPD/emphysema (in which inhaled anticholinergic medications such as Spiriva/tiotropium oripratropium are standard-of-care treatment) and asthma, particularly for exercise-related asthma exacerbations, which may have a component of autonomic dysregulation.
