Arcuate nucleus (medulla)

Arcuate nucleus (medulla)
	Transverse section of medulla oblongata below the middle of the olive. ("Nucleus arcuatus" visible near bottom right.)
	Dissection of brain-stem. Lateral view. (Labels for "External arcuate fibers" and "Dorsal external arcuate fibers" visible at lower right.)
Details
Identifiers
Latin	nucleus arcuatus medullae oblongatae
NeuroNames	775
NeuroLex ID	birnlex_2635
TA	A14.1.04.256
FMA	72609
	Anatomical terms of neuroanatomy [ edit on Wikidata]

Last updated March 10, 2019

In the medulla oblongata, the arcuate nucleus is a group of neurons located on the anterior surface of the medullary pyramids. These nuclei are the extension of the pontine nuclei. They receive fibers from the corticospinal tract and send their axons through the anterior external arcuate fibers and medullary striae to the cerebellum via the inferior cerebellar peduncle.

The medulla oblongata is a long stem-like structure located in the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers and therefore deals with the autonomic functions of breathing, heart rate and blood pressure.

A neuron, also known as a neurone and nerve cell, is an electrically excitable cell that communicates with other cells via specialized connections called synapses. All multicellular organisms except sponges and Trichoplax have neurons. A neuron is the main component of nervous tissue.

The medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit of the pyramids is marked when the fibers cross (decussate).

Arcuate nuclei are capable of chemosensitivity and have a proven role in the respiratory center controlling the breathing rate.

A chemoreceptor, also known as chemosensor, is a specialized sensory receptor cell which transduces (converts) a chemical substance and generates a biological signal. This signal may be in the form of an action potential if the chemoreceptor is a neuron, or in the form of a neurotransmitter that can activate a nearby nerve fiber if the chemosensor is a specialized sensory receptor cell, such as the taste receptor in a taste bud or in an internal peripheral chemoreceptor such as the carotid body. In more general terms, a chemosensor detects toxic or hazardous chemicals in the internal or external environment of the human body and transmits that information to the central nervous system,, in order to expel the biologically active toxins from the blood, and prevent further consumption of alcohol and/or other acutely toxic recreational intoxicants.

The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic centre and the apneustic centre.

The respiratory rate is the rate at which breathing occurs. This is usually measured in breaths per minute and is set, and controlled by the respiratory centre.

Additional images

Diagram showing the course of the arcuate fibers.
The formatio reticularis of the medulla oblongata, shown by a transverse section passing through the middle of the olive.

External links

Loyola University Chicago is a private Catholic research university in Chicago, Illinois. Founded in 1870 by the Jesuits, today Loyola is one of the largest Catholic universities in the United States. Loyola's professional schools have educated generations of local business and civic leaders, and distinguished programs in medicine, nursing, and health sciences are anchored by the nationally recognized Loyola University Medical Center.

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The pons is part of the brainstem, and in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.

The brainstem is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.

The glossopharyngeal nerve, known as the ninth cranial nerve, is a mixed nerve that carries afferent sensory and efferent motor information. It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest.

The medial lemniscus, also known as Reil's band or Reil's ribbon, is a large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

The nucleus ambiguus is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of nerves that innervate the muscles of the soft palate, pharynx, and larynx which are strongly associated with speech and swallowing. As well as motor neurons, the nucleus ambiguus in its "external formation" contains cholinergic preganglionic parasympathetic neurons for the heart.

Medial medullary syndrome, also known as inferior alternating syndrome, hypoglossal alternating hemiplegia, lower alternating hemiplegia, or Dejerine syndrome, is a type of alternating hemiplegia characterized by a set of clinical features resulting from occlusion of the anterior spinal artery. This results in the infarction of medial part of the medulla oblongata.

One of the dorsal column nuclei, the cuneate nucleus is a wedge-shaped nucleus in the closed part of the medulla oblongata, in the brainstem. It contains cells that give rise to the cuneate tubercle, visible on the posterior aspect of the medulla. It lies laterally to the gracile nucleus and medial to the spinal trigeminal nucleus in the medulla.

The corticobulbar tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract.

In anatomy, the olivary bodies or simply olives are a pair of prominent oval structures in the medulla oblongata, the lower portion of the brainstem. They contain the olivary nuclei.

The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.

In human anatomy, the anterior spinal artery is the artery that supplies the anterior portion of the spinal cord. It arises from branches of the vertebral arteries and courses along the anterior aspect of the spinal cord. It is reinforced by several contributory arteries, especially the artery of Adamkiewicz.

Vestibular nuclei cranial nuclei for the vestibular nerve

The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve.

Cerebellar peduncles connect the cerebellum to the brain stem. There are six cerebellar peduncles in total, three on each side:

The anterior external arcuate fibers vary as to their prominence: in some cases they form an almost continuous layer covering the medullary pyramids and olivary body, while in other cases they are barely visible on the surface.

The internal arcuate fibers are the axons of second-order sensory neurons that compose the gracile and cuneate nuclei of the medulla oblongata. These second-order neurons begin in the posterior grey column in the spinal cord. They receive input from first-order sensory neurons, which provide sensation to many areas of the body and have cell bodies in the dorsal root ganglia of the dorsal root of the spinal nerves. Upon decussation from one side of the medulla to the other, also known as the sensory decussation, they are then called the medial lemniscus.

In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the junction between the spinal cord and the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column-medial lemniscus pathway, which carries fine touch and proprioceptive information from the body to the brain. Each nucleus has an associated nerve tract, the gracile fasciculus and the cuneate fasciculus.

Anterior median fissure of the medulla oblongata

The anterior median fissure contains a fold of pia mater, and extends along the entire length of the medulla oblongata: It ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum.