Solitary nucleus

Template:Short description Template:Infobox brain The solitary nucleus (SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) 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.<ref name="Carpenter2">Template:Cite book</ref>

The solitary nucleus receives general visceral and special visceral inputs from the facial nerve (CN VII), glossopharyngeal nerve (CN IX) and vagus nerve (CN X); 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.<ref name="Haines2018">Template:Cite book</ref><ref name="Conn2008">Template:Cite book</ref> The cells involved in taste are the part of the solitary nucleus referred to as the gustatory nucleus.<ref name="Carpenter1">Template:Cite book</ref>

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 (with afferents from the anterior part of the tongue and roof of oral cavity rostral-most, and those from the larynx and epiglottis more caudally placed); gastrointestinal, cardiovascular, respiratory neurons are situated more caudally. However, some localization/organization also occurs along the ventro-dorsal and medio-lateral axes.<ref name=":2242">Template:Cite book</ref>

Afferents

• Gustatory (taste) sensation from facial nerve (CN VII) via the chorda tympani (from anterior 2/3 of tongue), glossopharyngeal nerve (CN IX) (from posterior 1/3 of tongue), and vagus nerve (CN X) (from epiglottis).Template:Citation needed
• Chemoreceptors and mechanoreceptors of the general visceral afferent pathway (GVA) from the carotid body and carotid sinus via (the carotid sinus nerve of) CN IX; from aortic bodies and aortic arch via CN X.
• Chemoreceptors and mechanoreceptors of the general visceral afferent pathway (GVA) 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.<ref>Template:Cite journal</ref> Additional minor GVA input from the nasal cavity, soft palate and sinus cavities enters via the facial nerve.<ref>Template:Cite book</ref>

Non-sensory afferent projections include:

• medial zone of hypothalamus → dorsal longitudinal fasciculus → periaqueductal gray → autonomic input of solitary nucleus<ref>Template:Cite book</ref>Template:Rp

Efferents

The solitary nucleus projects to numerous regions of the CNS, including:

• thalamus (mediates autonomic responses,<ref name="Conn2008" /> conscious taste sensation,Template:Citation needed conscious visceral sensations like stomach fullness/emptiness<ref>Template:Cite book</ref>)
  • (medial-most portion of) ventral posteromedial nucleus of thalamus → (via third-order neuron) sensory cortex and insular cortex<ref name=":2242" />
• paraventricular nucleus of<ref name=":0" /> hypothalamus → limbic system<ref name=":2242" /> (mediates autonomic responses)<ref name="Conn2008" /><ref name=":2242" />
• reticular formation (mediates autonomic responses)<ref name="Conn2008" /><ref name=":2242" />
• parasympathetic preganglionic neurons (for autonomic responses)<ref name="Conn2008" />
• central nucleus of the amygdala<ref name=":0" />
• parabrachial area<ref name=":0" />
• locus coeruleus<ref name=":0" />
• dorsal raphe nucleus<ref name=":0" />
• solitariospinal tract → upper levels of spinal cord<ref name=":2242" />
• other visceral motor or respiratory centers<ref name=":0">Template:Cite book</ref>

The SN projects to multiple other cranial nerve nuclei:<ref name="Haines2004">Template:Cite book</ref>

• salivatory nuclei
• hypoglossal nucleus
• dorsal nucleus of vagus nerve
• nucleus ambiguus (to mediate gag reflex)

Function

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.Template:Reference needed

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.Template:Reference needed

Gag reflex arc

The afferent limb of the gag reflex arc is conveyed by sensory afferents of the CN IX which terminate in the SN; the SN then projects to the nucleus ambiguus which in turn gives rise to motor efferent fibers of the CN IX/X which then mediate the efferent limb of the arc.<ref name="Haines2004">Template:Cite book</ref>

Additional images

• Section of the medulla oblongata at about the middle of the olive.
  Section of the medulla oblongata at about the middle of the olive.
• Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view.
  Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view.

External links

• Template:BrainMaps