The solitary nucleus (SN) (nucleus of the solitary tract, nucleus solitarius, or nucleus tractus solitarii) is a series of

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s 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 The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(CN VII),

glossopharyngeal nerve The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper Medulla oblongata, medulla, just anterior (closer to the nose) to t ...

(CN IX) and

vagus nerve The vagus nerve, also known as the tenth cranial nerve (CN X), plays a crucial role in the autonomic nervous system, which is responsible for regulating involuntary functions within the human body. This nerve carries both sensory and motor fibe ...

(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. 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

s in the medulla oblongata. Their cell bodies form a roughly vertical column of grey matter in the medulla oblongata. Their

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s form an enclosed

nerve tract A nerve tract is a bundle of nerve fibers (axons) connecting Nucleus (neuroanatomy), nuclei of the central nervous system. In the peripheral nervous system, this is known as a nerve fascicle, and has associated nervous tissue, connective tissue. T ...

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.

Afferents

* Gustatory (taste) sensation from facial nerve (CN VII) via the

chorda tympani Chorda tympani is a branch of the facial nerve that carries gustatory (taste) sensory innervation from the front of the tongue and parasympathetic ( secretomotor) innervation to the submandibular and sublingual salivary glands. Chorda tymp ...

(from anterior 2/3 of tongue), glossopharyngeal nerve (CN IX) (from posterior 1/3 of tongue), and vagus nerve (CN X) (from epiglottis). * Chemoreceptors and mechanoreceptors of the general visceral afferent pathway (GVA) from the carotid body and

carotid sinus In human anatomy, the carotid sinus is a dilated area at the base of the internal carotid artery just superior to the bifurcation of the internal carotid and external carotid at the level of the superior border of thyroid cartilage. The carot ...

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. Additional minor GVA input from the nasal cavity, soft palate and sinus cavities enters via the facial nerve. Non-sensory afferent projections include: * medial zone of

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

→ dorsal longitudinal fasciculus → periaqueductal gray → autonomic input of solitary nucleus

Efferents

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

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

(mediates autonomic responses, conscious taste sensation, conscious visceral sensations like stomach fullness/emptiness) ** (medial-most portion of) ventral posteromedial nucleus of

→ (via third-order neuron) sensory cortex and

insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...

* paraventricular nucleus of

→ limbic system (mediates autonomic responses) * reticular formation (mediates autonomic responses) * parasympathetic preganglionic neurons (for autonomic responses) * 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 The SN projects to multiple other cranial nerve nuclei: * 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 pharyngeal reflex or gag reflex is a reflex muscular contraction of the back of the throat, evoked by touching the roof of the mouth, back of the tongue, area around the tonsils, uvula, and back of the throat. It, along with other aerodigest ...

, the

reflex, the aortic reflex, the cough reflex, the baroreflex and chemoreceptor reflexes, several respiratory reflexes and reflexes within the gastrointestinal system regulating

motility Motility is the ability of an organism to move independently using metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...

and secretion. Neurons which transmit signals about the gut wall, the stretch of the

lungs The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syste ...

, and the dryness of

mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

s also innervate the SN. The first central neurons within the SN can participate in simple autonomic reflexes.

Gag reflex arc

The afferent limb of the

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.

Additional images

File:Gray694.png, Section of the medulla oblongata at about the middle of the olive. File:Gray698.png, Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view.

References

External links

* {{Authority control Cranial nerve nuclei Medulla oblongata Vagus nerve Glossopharyngeal nerve Facial nerve