![]() The nucleus ambiguus, therefore, is an important modulator in cardiac activity and protective reflexes. Activation of this receptor induces bradycardia, indicating the cardioprotective mechanism of estrogen on the heart. Multiple other peptides and receptors have been implicated in the complex feedback loop of cardiac vagal tone via the nucleus ambiguus, including the G-protein coupled estrogen receptor in the nucleus ambiguus. Bradykinin stimulates the B1 and B2 receptors in the nucleus ambiguus, causing an increase in cytosolic calcium (Ca2+) release and depolarization of the neurons. Bradykinin, an endogenous peptide that has cardioprotective and vasodilatory properties, acts on receptors on the nucleus ambiguus to induce bradycardia. Modulation of this parasympathetic reflex is via peptides such as bradykinin. Conversely, when the heart rate becomes too low, this parasympathetic response is not activated, allowing the heart rate to rise appropriately. The tonic inhibition of the heart rate serves a cardioprotective function. The cells of NTS send excitatory signals to the nucleus ambiguus, which then sends inhibitory signals to the sinoatrial node via CN X to reduce the heart rate. These signals get carried by the afferent nerve branches of CN IX and CN X. When heart rate increases, baroreceptor afferents are activated and terminate in the nucleus tractus solitarius (NTS) in the medulla. The nucleus ambiguus contains vagal efferent neurons that inhibit the heart rate. Nucleus solitarius receives the baroreceptor sensory input, while the nucleus ambiguus (and dorsal motor nucleus to a lesser extent) are involved in the parasympathetic output. The vagus nerve, which has various motor, sensory, and autonomic functions involving multiple organ systems, is associated with three main nuclei in the brainstem: the dorsal motor nucleus, nucleus ambiguus, and nucleus solitarius. The muscles controlled by the nucleus ambiguus initiate the mechanism of swallowing and phonation.Īdditionally, the nucleus contributes to parasympathetic cardiac regulation. ![]() ![]() It gives rise to the efferent motor fibers of the vagus nerve (CN X) that innervate the muscles of the soft palate, larynx, pharynx, as well as the stylopharyngeus muscles and pharyngeal constrictor muscles of the glossopharyngeal nerve (CN IX). The nucleus ambiguus is involved in the motor functions of swallowing and speech. The nuclei are in the lateral regions of the rostral medulla posterior to the inferior olive. Its location is in the reticular formation of the medulla oblongata, the lowest part of the brainstem. The nucleus ambiguus is the location of cell bodies of motor nerves that innervate the ipsilateral muscles of the soft palate, pharynx, larynx and upper esophagus and are mainly responsible for swallowing and speaking.
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