The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

. It is anterior and partially inferior to the

cerebellum The cerebellum (: cerebella or cerebellums; Latin for 'little brain') is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as it or eve ...

. It is a cone-shaped

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 ...

al mass responsible for autonomic (involuntary) functions, ranging from

vomiting Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, pre ...

sneezing A sneeze (also known as sternutation) is a semi-autonomous, convulsive expulsion of air from the lungs through the nose and mouth, usually caused by foreign particles irritating the nasal mucosa. A sneeze expels air forcibly from the mouth a ...

. The medulla contains the cardiovascular center, the

respiratory center 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 ...

and

vasomotor Vasomotor refers to actions upon a blood vessel which alter its diameter. More specifically, it can refer to vasodilator action and vasoconstrictor action. Control Sympathetic innervation Sympathetic nerve fibers travel around the tunica media ...

centers, responsible for the autonomic functions of

breathing Breathing (spiration or ventilation) is the rhythmical process of moving air into ( inhalation) and out of ( exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxy ...

heart rate Heart rate is the frequency of the cardiac cycle, heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's Human body, physical needs, including the nee ...

and

blood pressure Blood pressure (BP) is the pressure of Circulatory system, circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term ...

as well as the

sleep–wake cycle A circadian rhythm (), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., endogenous) and responds to the environment (is entrai ...

. "Medulla" is from Latin, ‘pith or marrow’. And "oblongata" is from Latin, ‘lengthened or longish or elongated'. During embryonic development, the medulla oblongata develops from the

myelencephalon The myelencephalon or afterbrain is the most posterior region of the embryonic hindbrain, from which the medulla oblongata develops. Myelencephalon is from myel- (bone marrow or spinal cord) and encephalon (the vertebrate brain). Development ...

. The myelencephalon is a secondary

brain vesicle Brain vesicles are the bulge-like enlargements of the early development of the neural tube in vertebrates, which eventually give rise to the brain. Vesicle formation begins shortly after the rostral closure of the neural tube, at about embryoni ...

which forms during the maturation of the

rhombencephalon The hindbrain, rhombencephalon (shaped like a rhombus) is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together they support vital bodily processes. Met ...

, also referred to as the hindbrain. The bulb is an archaic term for the medulla oblongata. In modern clinical usage, the word bulbar (as in bulbar palsy) is retained for terms that relate to the medulla oblongata, particularly in reference to

medical conditions A disease is a particular abnormal condition that adversely affects the structure or function of all or part of an organism and is not immediately due to any external injury. Diseases are often known to be medical conditions that are asso ...

. The word bulbar can refer to the

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s and

tracts Tract may refer to: Geography and real estate * Housing tract, an area of land that is subdivided into smaller individual lots * Land lot or tract, a section of land * Census tract, a geographic region defined for the purpose of taking a census ...

connected to the medulla such as the

corticobulbar tract The corticobulbar (or corticonuclear) tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the Medullary pyramids (brainstem), medullary pyramids, which are part of the brainstem's medulla oblonga ...

, and also by association to those

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s innervated, including those of the

tongue The tongue is a Muscle, muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for chewing and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper s ...

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

and

larynx The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...

Anatomy

Medulla oblongata and foramen magnum animation small

The medulla can be thought of as being in two parts: * an upper open part or superior part where the dorsal surface of the medulla is formed by the

fourth ventricle The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ...

. * a lower closed part or inferior part where the fourth ventricle has narrowed at the

obex The obex () is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord. Cerebrospinal fluid can flow from the fourth ventricle into the obex. In anatomical studies, the obex has been fo ...

in the caudal medulla, and surrounds part of the

central canal The central canal (also known as spinal foramen or ependymal canal) is the cerebrospinal fluid-filled space that runs through the spinal cord. The central canal lies below and is connected to the ventricular system of the brain, from which it r ...

External surfaces

The anterior median fissure contains a fold of

pia mater Pia mater ( or ),Entry "pia mater"
in
pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other mammals, lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of ...

in a small triangular area, termed the foramen cecum. On either side of this fissure are raised areas termed the

medullary pyramids In neuroanatomy, 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 ...

. The pyramids house the

pyramidal tracts The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''cort ...

–the

corticospinal tract The corticospinal tract is a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk. There are more than one million neu ...

, and the

of the nervous system. At the caudal part of the medulla these tracts cross over in the decussation of the pyramids obscuring the fissure at this point. Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the anterior external arcuate fibers. The region between the anterolateral and posterolateral sulcus in the upper part of the medulla is marked by a pair of swellings known as olivary bodies (also called ''olives''). They are caused by the largest nuclei of the olivary bodies, the inferior olivary nuclei. The posterior part of the medulla between the posterior median sulcus and the posterolateral sulcus contains tracts that enter it from the posterior funiculus of the spinal cord. These are the gracile fasciculus, lying medially next to the midline, and the cuneate fasciculus, lying laterally. These fasciculi end in rounded elevations known as the gracile and the cuneate tubercles. They are caused by masses of

gray 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, and ...

known as the gracile nucleus and the

cuneate nucleus The dorsal column nuclei are a pair of nuclei in the dorsal columns of the dorsal column–medial lemniscus pathway (DCML) in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are situated at the l ...

. The soma (cell bodies) in these nuclei are the second-order neurons of the posterior column-medial lemniscus pathway, and their axons, called the internal arcuate fibers or fasciculi, decussate from one side of the medulla to the other to form the

medial lemniscus The medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate in the brainstem The brainstem (or brain stem) is the pos ...

. Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the

. The fossa is bounded on either side by the

inferior cerebellar peduncle The inferior cerebellar peduncle is formed by fibers of the restiform body that join with fibers from the much smaller juxtarestiform body. The inferior cerebellar peduncle is the smallest of the three cerebellar peduncles. The upper part of t ...

, which connects the medulla to the

. The lower part of the medulla, immediately lateral to the cuneate fasciculus, is marked by another longitudinal elevation known as the tuberculum cinereum. It is caused by an underlying collection of gray matter known as the

spinal trigeminal nucleus The spinal trigeminal nucleus is a nucleus in the medulla that receives information about deep/crude touch, pain, and temperature from the ipsilateral face. In addition to the trigeminal nerve (CN V), the facial (CN VII), glossopharyngeal (CN ...

. The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

. The base of the medulla is defined by the

commissural fibers The commissural fibers or transverse fibers are axons that connect the two hemispheres of the brain. Huge numbers of commissural fibers make up the commissural tracts in the brain, the largest of which is the corpus callosum. In contrast to ...

, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.

Blood supply

Blood to the medulla is supplied by a number of

arteries An artery () is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in ...

. * Anterior spinal artery: This supplies the whole medial part of the medulla oblongata. * Posterior inferior cerebellar artery: This is a major branch of the vertebral artery, and supplies the posterolateral part of the medulla, where the main sensory tracts run and

synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...

. It also supplies part of the cerebellum. * Direct branches of the

vertebral artery The vertebral arteries are major artery, arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, m ...

: The vertebral artery supplies an area between the anterior spinal and posterior inferior cerebellar arteries, including the solitary nucleus and other sensory nuclei and fibers. * Posterior spinal artery: This supplies the dorsal column of the closed medulla containing

fasciculus gracilis ''Fasciculus vesanus'' is an extinct species of stem group, stem-group Ctenophora, ctenophores known from the Burgess Shale of British Columbia, Canada. It is dated to and belongs to middle Cambrian strata. The species is remarkable for its tw ...

, gracile nucleus, fasciculus cuneatus, and

Development

The medulla oblongata forms in

fetal development Prenatal development () involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...

from the

. The final differentiation of the medulla is seen at week 20 gestation. Neuroblasts from the

alar plate The alar plate (or alar lamina) is a neural structure in the embryonic nervous system, part of the dorsal side of the neural tube, that involves the communication of general somatic and general visceral sensory impulses. The caudal part later ...

of the

neural tube In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, ...

at this level will produce the sensory nuclei of the medulla. The basal plate neuroblasts will give rise to the motor nuclei. *

Alar plate The alar plate (or alar lamina) is a neural structure in the embryonic nervous system, part of the dorsal side of the neural tube, that involves the communication of general somatic and general visceral sensory impulses. The caudal part later ...

neuroblasts give rise to: ** The solitary nucleus, which contains the

general visceral afferent fibers The general visceral afferent (GVA) fibers conduct sensory impulses (usually pain or reflex sensations) from the internal organs, glands, and blood vessels to the central nervous system. They are considered to be part of the visceral nervous sy ...

for

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

, as well as the special visceral afferent column. ** The spinal

trigeminal nerve nuclei The sensory trigeminal nerve nuclei are the largest of the cranial nerve nuclei, and extend through the whole of the midbrain, pons and medulla, and into the upper cervical spinal cord. The nucleus is divided into three parts, from rostral to ...

which contains the general somatic afferent column. ** The cochlear and

vestibular nuclei The vestibular nuclei (VN) are the cranial nuclei for the vestibular nerve located in the brainstem. In Terminologia Anatomica, they are grouped in both the pons and the medulla in the brainstem The brainstem (or brain stem) is the poste ...

, which contain the

special somatic afferent Special somatic afferent fibers (SSA) are the afferent nerve fibers that carry information from the special senses of vision, hearing and balance. The cranial nerves containing SSA fibers are the optic nerve (CN II) and the vestibulocochlear nerve ...

column. ** The

inferior olivary nucleus The inferior olivary nucleus (ION) is a structure found in the medulla oblongata underneath the superior olivary nucleus.Gado, Thomas A. Woolsey; Joseph Hanaway; Mokhtar H. (2003). The brain atlas a visual guide to the human central nervous syste ...

, which relays to the cerebellum. ** The dorsal column nuclei, which contain the gracile and cuneate nuclei. * Basal plate neuroblasts give rise to: ** The

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 ...

, which contains

general somatic efferent fibers The general (spinal) somatic efferent neurons (GSE, somatomotor, or somatic motor fibers) arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord. They exit the spinal cord through the ventral roots, carry ...

. ** The

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 ...

, which form the

special visceral efferent Special visceral efferent fibers (SVE) are the efferent nerve fibers that provide motor innervation to the muscles of the pharyngeal arches in humans, and the branchial arches in fish. Some sources prefer the term "branchiomotor" or "branchial ef ...

. ** The

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 ...

and the inferior salivatory nucleus, both of which form the

general visceral efferent fibers General visceral efferent fibers (GVE), visceral efferents or autonomic efferents are the efferent nerve fibers of the autonomic nervous system (also known as the ''visceral efferent nervous system'') that provide motor innervation to smooth musc ...

Function

The medulla oblongata connects the higher levels of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

to the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

, and is responsible for several functions of the

autonomous nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system ...

which include: * The control of ventilation via signals from the

carotid In anatomy, the left and right common carotid arteries (carotids) () are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries. Structure The common carotid a ...

and

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 ...

Respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

is regulated by groups of

chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorece ...

s. These sensors detect changes in the acidity of the blood; if, for example, the blood becomes too acidic, the medulla oblongata sends electrical signals to intercostal and phrenical muscle tissue to increase their contraction rate and increase oxygenation of the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

. The

ventral respiratory group Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

and the

dorsal respiratory group 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 res ...

are neurons involved in this regulation. The

pre-Bötzinger complex The preBötzinger complex, often abbreviated as preBötC, is a functionally and anatomically specialized site in the ventral-lateral region of the lower medulla oblongata (i.e., lower brainstem). The preBötC is part of the ventral respiratory group ...

is a cluster of interneurons involved in the respiratory function of the medulla. * Cardiovascular center – sympathetic,

parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The autonomic nervous system is responsible for regulat ...

* Vasomotor center –

baroreceptor Baroreceptors (or archaically, pressoreceptors) are stretch receptors that sense blood pressure. Thus, increases in the pressure of blood vessel triggers increased action potential generation rates and provides information to the central nervous s ...

s *

Reflex In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...

centers of vomiting, coughing, sneezing and swallowing. These reflexes which include the

pharyngeal 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

swallowing Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mou ...

reflex (also known as the palatal reflex), and the masseter reflex can be termed ''bulbar'' reflexes.
/ref>

Clinical significance

A Vascular occlusion, blood vessel blockage (such as in a

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

) will injure the

pyramidal tract The pyramidal tracts include both the corticobulbar tract and the corticospinal tract. These are aggregations of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and terminate either in the brainstem (''cort ...

, and the

. This causes a syndrome called medial medullary syndrome. Lateral medullary syndrome can be caused by the blockage of either the posterior inferior cerebellar artery or of the vertebral arteries. Progressive bulbar palsy (PBP) is a disease that attacks the nerves supplying the bulbar muscles. Infantile progressive bulbar palsy is progressive bulbar palsy in children.

Other animals

Both lampreys and hagfish possess a fully developed medulla oblongata. Since these are both very similar to early agnathans, it has been suggested that the medulla evolved in these early fish, approximately 505 million years ago. Haycock, ''Being and Perceiving'' The status of the medulla as part of the primordial reptilian brain is confirmed by its disproportionate size in modern

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s such as the

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...

alligator An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...

, and

monitor lizard Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and West African Nile monitor, one species is also found in south America as an invasive species. A ...

Additional images

File:Cerebrum lobes.svg, Lobes File:Medulla Oblongata and Cerebellum.svg, Cross section of the medulla (in red) and surrounding tissues. File:Gray679.png, Anteroinferior view of the medulla oblongata and pons. File:Gray724.png, Base of brain. File:Gray768.png, Diagram showing the positions of the three principal subarachnoid cisternæ. File:Medulla oblongata - posterior - very low mag.jpg,

Micrograph A micrograph is an image, captured photographically or digitally, taken through a microscope or similar device to show a magnify, magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken ...

of the posterior portion of the ''open part'' of the medulla oblongata, showing the

(top of image) and the nuclei of CN XII (medial) and CN X (lateral). H&E-LFB stain.

References

External links

* {{DEFAULTSORT:Medulla Oblongata