Solitary nucleus
The solitary nucleus '' is a series of neurons whose cell bodies form a roughly vertical column of grey matter in the medulla oblongata of the brainstem. Their axons form the bulk of the enclosed solitary tract. The solitary nucleus can be divided into different parts including dorsomedial, dorsolateral, and ventrolateral subnuclei.
The solitary nucleus receives general visceral and special visceral inputs from the facial nerve, glossopharyngeal nerve and vagus nerve ; it receives and relays stimuli related to taste and visceral sensation. It sends outputs to various parts of the brain, such as the hypothalamus, thalamus, and reticular formation, forming circuits that contribute to autonomic regulation.
Cells along the length of the SN are arranged roughly in accordance with function; for instance, cells involved in taste are located in the rostral part, while those receiving information from cardio-respiratory and gastrointestinal processes are found in the caudal part. The cells involved in taste are the part of the solitary nucleus referred to as the gustatory nucleus.
Anatomy
The solitary nucleus is a series of neurons in the medulla oblongata. Their cell bodies form a roughly vertical column of grey matter in the medulla oblongata. Their axons form an enclosed nerve tract called the solitary tract.Viscerotopic organization
Neurons of the SN are notably functionally arranged roughly length-wise along the nucleus: gustatory neurons are situated rostrally ; gastrointestinal, cardiovascular, respiratory neurons are situated more caudally. However, some localization/organization also occurs along the ventro-dorsal and medio-lateral axes.Afferents
- Gustatory sensation from facial nerve via the chorda tympani, glossopharyngeal nerve , and vagus nerve .
- Chemoreceptors and mechanoreceptors of the general visceral afferent pathway from the carotid body and carotid sinus via CN IX; from aortic bodies and aortic arch via CN X.
- Chemoreceptors and mechanoreceptors of the general visceral afferent pathway with endings located in the heart, lungs, airways, gastrointestinal system, pharynx, and liver via the glossopharyngeal and vagus nerves. Organ specific regions of neuronal architecture are preserved in the solitary nucleus. Additional minor GVA input from the nasal cavity, soft palate and sinus cavities enters via the facial nerve.
- medial zone of hypothalamus → dorsal longitudinal fasciculus → periaqueductal gray → autonomic input of solitary nucleus
Efferents
- thalamus
- * ventral posteromedial nucleus of thalamus → sensory cortex and insular cortex
- paraventricular nucleus of hypothalamus → limbic system
- reticular formation
- parasympathetic preganglionic neurons
- central nucleus of the amygdala
- parabrachial area
- locus coeruleus
- dorsal raphe nucleus
- solitariospinal tract → upper levels of spinal cord
- other visceral motor or respiratory centers
Afferents of the SN mediate the gag reflex, the carotid sinus reflex, the aortic reflex, the cough reflex, the baroreflex and chemoreceptor reflexes, several respiratory reflexes, the belch reflex, and other reflexes within the gastrointestinal system that regulate motility and secretion.
Neurons which transmit signals about the gut wall, the stretch of the lungs, and the dryness of mucous membranes also innervate the SN. The first central neurons within the SN can participate in simple autonomic reflexes.