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 Grey matter, or gray matter in American English, is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil ( dendrites and unmyelinated axons), glial cells ( astrocytes and oligodendrocytes), synapses, ...

in the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...

of the brainstem. Their axons form the bulk of the enclosed

solitary tract The solitary tract (tractus solitarius or fasciculus solitarius) is a compact fiber bundle that extends longitudinally through the posterolateral region of the medulla oblongata. The solitary tract is surrounded by the solitary nucleus, and desc ...

. 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 The gustatory nucleus is the rostral part of the solitary nucleus located in the medulla oblongata. The gustatory nucleus is associated with the sense of taste and has two sections, the rostral and lateral regions. A close association between the ...

Anatomy

The solitary nucleus is a series of

s in the

. Their

cell bodies In cellular neuroscience, the soma (: somata or somas; ), neurocyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. Although it is often used to refer to neurons, it can also ...

form a roughly vertical column of

in the

. 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

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 The carotid body is a small cluster of peripheral chemoreceptor cells and supporting sustentacular cells situated at the bifurcation of each common carotid artery in its tunica externa. The carotid body detects changes in the composition of art ...

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 The carotid branch of the glossopharyngeal nerve (carotid sinus nerve or Hering's nerve) is a small branch of the glossopharyngeal nerve (cranial nerve IX) that innervates the carotid sinus, and carotid body. Anatomy Course and relations It ...

of) CN IX; from

aortic bodies The aortic bodies are one of several small clusters of peripheral chemoreceptors located along the aortic arch. They are important in measuring partial pressures of oxygen and carbon dioxide in the blood, and blood pH. Structure The aortic b ...

and

aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea. Structure The aorta begins ...

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 The dorsal longitudinal fasciculus (DLF) is a distinctive nerve tract in the midbrain. It extends from the hypothalamus rostrally to the spinal cord caudally, and contains both descending and ascending fibers. Descending fibers arise in the hyp ...

→

periaqueductal gray The periaqueductal gray (PAG), also known as the central gray, is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for ...

→ 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 The ventral posteromedial nucleus (VPM) is a nucleus within the ventral posterior nucleus of the thalamus and serves an analogous somatosensory relay role for the ascending trigeminothalamic tracts as its lateral neighbour the ventral posterolat ...

→ (via third-order neuron)

sensory cortex The sensory cortex can refer sometimes to the primary somatosensory cortex, or it can be used as a term for the primary and secondary cortices of the different senses (two cortices each, on left and right hemisphere): the visual cortex on the occ ...

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 The paraventricular nucleus (PVN) is a nucleus in the hypothalamus, located next to the third ventricle. Many of its neurons project to the posterior pituitary where they secrete oxytocin, and a smaller amount of vasopressin. Other secretions ...

→

limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''P ...

(mediates autonomic responses) *

reticular formation The reticular formation is a set of interconnected nuclei in the brainstem that spans from the lower end of the medulla oblongata to the upper end of the midbrain. The neurons of the reticular formation make up a complex set of neural networks ...

(mediates autonomic responses) * parasympathetic preganglionic neurons (for autonomic responses) *

central nucleus of the amygdala The central nucleus of the amygdala (CeA or aCeN) is a nucleus within the amygdala. It serves as the major output nucleus of the amygdala and participates in receiving and processing pain information. CeA connects with brainstem areas that cont ...

parabrachial area The parabrachial nuclei, also known as the parabrachial complex, are a group of nuclei in the dorsolateral pons that surrounds the superior cerebellar peduncle as it enters the brainstem from the cerebellum. They are named from the Latin term for ...

locus coeruleus The locus coeruleus () (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system in the reticular ...

dorsal raphe nucleus The dorsal raphe nucleus is one of the raphe nuclei. It is situated in the brainstem at the midline. It has rostral and caudal subdivisions: * The rostral aspect of the ''dorsal'' raphe is further divided into interfascicular, ventral, ventrolater ...

solitariospinal tract The solitariospinal tract is a descending nerve tract that controls breathing by promoting the action of inspiratory muscles (note that exhalation is usually passive). It consists of a small group of axons originating in the nucleus solitarius of t ...

→ upper levels of spinal cord * other visceral motor or respiratory centers The SN projects to multiple other

cranial nerve nuclei A cranial nerve nucleus is a collection of neuron cell bodies (gray matter) in the brain stem that is associated with one or more of the cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nucl ...

: *

salivatory nuclei The salivatory nuclei are two general visceral efferent nuclei located in the caudal pons, dorsal and lateral to the facial nucleus. Their neurons give rise to preganglionic parasympathetic nerve fibers in the control of salivation.Digital vers ...

hypoglossal nucleus The hypoglossal nucleus is a cranial nerve nucleus, found within the medulla. Being a motor nucleus, it is close to the midline. In the open medulla, it is visible as what is known as the '' hypoglossal trigone'', a raised area (medial to the v ...

dorsal nucleus of vagus nerve The dorsal nucleus of vagus nerve (or posterior nucleus of vagus nerve or dorsal vagal nucleus or nucleus dorsalis nervi vagi or nucleus posterior nervi vagi) is a cranial nerve nucleus of the vagus nerve (CN X) situated in the medulla oblongata ...

nucleus ambiguus The nucleus ambiguus ("ambiguous nucleus" in English) is a group of large motor neurons, situated deep in the medullary part of the reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innerva ...

(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 cough reflex occurs when stimulation of cough receptors in the respiratory tract by dust or other foreign particles produces a cough, which causes rapidly moving air which usually remove the foreign material before it reaches the lungs. This ...

, the

baroreflex The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels. The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure cause ...

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

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