View source for Medulla oblongata

{{Short description|Structure of the brain stem}}
{{Use American English|date = April 2019}}
{{for multi|the film|Medulla Oblongata (film)|other uses|Medulla (disambiguation)}}
{{more citations needed|date=October 2010}}
{{Infobox brain
| Name            = Medulla oblongata
| Latin           = medulla oblongata, myelencephalon, bulbus
| Image           = 1311 Brain Stem.jpg
| Caption         = Medulla oblongata part of the [[brain stem]] ''(purple colored)''
| Image2          = Gray694.png
| Caption2        = Section of the medulla oblongata at about the middle of the [[olivary body]]
| Width           = 300
| IsPartOf        = [[Brain stem]]
| Components      = 
| Artery          =
| Vein            =
}}
The '''medulla oblongata''' or simply '''medulla''' is a long stem-like structure which makes up the lower part of the [[brainstem]].<ref name=":0">{{Citation|last=Webb|first=Wanda G.|title=2 - Organization of the Nervous System I|date=2017-01-01|url=http://www.sciencedirect.com/science/article/pii/B9780323100274000026|work=Neurology for the Speech-Language Pathologist (Sixth Edition)|pages=13–43|editor-last=Webb|editor-first=Wanda G.|publisher=Mosby|language=en|doi=10.1016/b978-0-323-10027-4.00002-6|isbn=978-0-323-10027-4|access-date=2020-11-15|url-access=subscription}}</ref> It is anterior and partially inferior to the [[cerebellum]]. It is a cone-shaped [[neuron]]al mass responsible for [[autonomic nervous system|autonomic]] (involuntary) functions, ranging from [[vomiting]] to [[sneezing]].<ref name=":1">{{Citation|last=Waldman|first=Steven D.|title=CHAPTER 120 - The Medulla Oblongata|date=2009-01-01|url=http://www.sciencedirect.com/science/article/pii/B9781416058939001209|work=Pain Review|pages=208|editor-last=Waldman|editor-first=Steven D.|place=Philadelphia|publisher=W.B. Saunders|language=en|doi=10.1016/b978-1-4160-5893-9.00120-9|isbn=978-1-4160-5893-9|access-date=2020-11-15|url-access=subscription}}</ref> The medulla contains the [[cardiovascular center]], the [[respiratory center]], [[Area postrema|vomiting]] and [[vasomotor]] centers, responsible for the autonomic functions of [[breathing]], [[heart rate]] and [[blood pressure]] as well as the [[Circadian rhythm|sleep–wake cycle]].<ref name=":1" /> "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 is a secondary [[brain vesicle]] which forms during the maturation of the [[rhombencephalon]], also referred to as the hindbrain.

The '''bulb''' is an archaic term for the medulla oblongata.<ref name=":0" /> 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 [[Disease|medical conditions]]. The word bulbar can refer to the [[nerve]]s and [[neural tract|tracts]] connected to the medulla such as the [[corticobulbar tract]], and also by association to those [[muscle]]s [[innervation|innervated]], including those of the [[tongue]], [[pharynx]] and [[larynx]].

==Anatomy==
[[File:Slide11ee.JPG|Medulla oblongata|thumb]]
[[File:Medulla oblongata and foramen magnum animation small.gif|220px|thumb|right|Medulla-animated as it protrudes from the [[foramen magnum]] of the [[skull-base]], after which it gives rise to the [[spinal cord]].]]
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]].
* a lower '''closed part''' or inferior part where the fourth ventricle has narrowed at the [[obex]] in the caudal medulla, and surrounds part of the [[Central canal of spinal cord|central canal]].

===External surfaces===
The [[Anterior median fissure of the medulla oblongata|anterior median fissure]] contains a fold of [[pia mater]], and extends along the length of the medulla oblongata. It ends at the lower border of the [[pons]] in a small triangular area, termed the [[Foramen cecum (frontal bone)|foramen cecum]]. On either side of this fissure are raised areas termed the [[medullary pyramids]]. The pyramids house the [[pyramidal tracts]]–the [[corticospinal tract]], and the [[corticobulbar tract]] 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 sulcus of medulla|anterolateral]] and [[posterolateral sulcus of medulla oblongata|posterolateral sulcus]] in the upper part of the medulla is marked by a pair of swellings known as [[Olivary body|olivary bodies]] (also called ''olives''). They are caused by the largest [[nucleus (neuroanatomy)|nuclei]] of the olivary bodies, the [[Inferior olivary nucleus|inferior olivary nuclei]].

The posterior part of the medulla between the [[posterior median sulcus of medulla oblongata|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]] known as the [[gracile nucleus]] and the [[cuneate nucleus]]. The [[soma (biology)|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]].

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 [[fourth ventricle]]. The fossa is bounded on either side by the [[inferior cerebellar peduncle]], which connects the medulla to the [[cerebellum]].

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 gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the [[trigeminal nerve]].  The base of the medulla is defined by the [[commissural fibers]], 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]].<ref>{{cite book |last=Purves |first=Dale |date=2001 |title=Neuroscience. 2nd edition. |chapter=The Blood Supply of the Brain and Spinal Cord |url=https://www.ncbi.nlm.nih.gov/books/NBK11042/ |publisher=Sinauer Associates}}</ref>

* [[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]]. It also supplies part of the cerebellum.
* Direct branches of the [[vertebral artery]]: 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 [[Gracile fasciculus|fasciculus gracilis]], [[gracile nucleus]], [[Cuneate fasciculus|fasciculus cuneatus]], and [[cuneate nucleus]].

===Development===
The medulla oblongata forms in [[prenatal development|fetal development]] from the [[myelencephalon]]. The final differentiation of the medulla is seen at week 20 gestation.<ref>Carlson, Neil R. Foundations of Behavioral Neuroscience.63-65</ref>{{Full citation needed | date = July 2019}}

[[Neuroblast]]s from the [[alar plate]] of the [[neural tube]] at this level will produce the sensory nuclei of the medulla. The [[basal plate (neural tube)|basal plate]] [[neuroblast]]s will give rise to the motor nuclei.
* [[Alar plate]] neuroblasts give rise to:
** The [[solitary nucleus]], which contains the [[general visceral afferent fibers]] for [[taste]], as well as the [[special visceral afferent]] column.
** The spinal [[trigeminal nerve nuclei]] which contains the [[General somatic afferent fiber|general somatic afferent column]].
** The [[Cochlear nuclei|cochlear]] and [[vestibular nuclei]], which contain the [[special somatic afferent]] column.
** The [[inferior olivary nucleus]], which relays to the cerebellum.
** The [[dorsal column nuclei]], which contain the [[gracile nucleus|gracile]] and [[cuneate nuclei]].
* [[Basal plate (neural tube)|Basal plate]] neuroblasts give rise to:
** The [[hypoglossal nucleus]], which contains [[general somatic efferent fibers]].
** The [[nucleus ambiguus]], which form the [[special visceral efferent]].
** The [[dorsal nucleus of vagus nerve]] and the [[inferior salivatory nucleus]], both of which form the [[general visceral efferent fibers]].

==Function==
The medulla oblongata connects the higher levels of the [[brain]] to the [[spinal cord]], and is responsible for several functions of the [[autonomous nervous system]] which include:
* The [[control of ventilation]] via signals from the [[carotid body|carotid]] and [[aortic body|aortic bodies]]. [[Respiration (physiology)|Respiration]] is regulated by groups of [[chemoreceptor]]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 muscle|intercostal]] and [[phrenic nerve|phrenical]] muscle tissue to increase their contraction rate and increase oxygenation of the [[blood]]. The [[ventral respiratory group]] and the [[dorsal respiratory group]] are neurons involved in this regulation. The [[pre-Bötzinger complex]] is a cluster of interneurons involved in the respiratory function of the medulla. 
* [[Cardiovascular center]] – sympathetic, [[parasympathetic nervous system]]
* [[Vasomotor center]] – [[baroreceptor]]s
* [[Reflex]] centers of vomiting, coughing, sneezing and swallowing. These reflexes which include the [[pharyngeal reflex]], the [[swallowing]] reflex (also known as the palatal reflex), and the [[masseter reflex]] can be termed ''bulbar'' reflexes.<ref>{{cite journal |last1=Hughes |first1=T. |year=2003 |title=Neurology of swallowing and oral feeding disorders: Assessment and management |journal=Journal of Neurology, Neurosurgery & Psychiatry |volume=74 |issue=90003 |pages=48iii–52 |doi=10.1136/jnnp.74.suppl_3.iii48 |pmc=1765635 |pmid=12933914}} [http://jnnp.bmj.com/content/74/suppl_3/iii48.full]</ref>

==Clinical significance==
A [[Vascular occlusion|blood vessel blockage]] (such as in a [[stroke]]) will injure the [[pyramidal tract]], [[medial lemniscus]], and the [[hypoglossal nucleus]]. 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.<ref name=Nishizawa>{{cite journal | author = Nishizawa H, Kishida R, Kadota T, Goris RC | title = Somatotopic organization of the primary sensory trigeminal neurons in the hagfish, Eptatretus burgeri | journal = J Comp Neurol | volume = 267 | issue = 2 | pages = 281–95 | year = 1988 | pmid = 3343402 | doi = 10.1002/cne.902670210 | first4 = Richard C. | last2 = Kishida | first2 = Reiji | last4 = Goris | last3 = Kadota | first3 = Tetsuo | s2cid = 45624479 }}</ref><ref name=Rovainen>{{cite journal | author = Rovainen CM | title = Respiratory bursts at the midline of the rostral medulla of the lamprey | journal = J Comp Physiol A | volume = 157 | issue = 3 | pages = 303–9 | year = 1985 | pmid = 3837091 | doi = 10.1007/BF00618120 | s2cid = 27654584 }}</ref> 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.<ref name=Haycock>[[#refHaycockDE|Haycock, ''Being and Perceiving'']]</ref>  The status of the medulla as part of the primordial [[reptilian brain]] is confirmed by its disproportionate size in modern [[reptile]]s such as the [[crocodile]], [[alligator]], and [[monitor lizard]].

==Additional images==
<gallery>
 File:Cerebrum lobes.svg|Lobes
 File:Medulla Oblongata and Cerebellum.svg|Cross section of the medulla (in red) and surrounding tissues.
 File:Gray679.png|[[Terms for anatomical location|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]] of the posterior portion of the ''open part'' of the medulla oblongata, showing the [[fourth ventricle]] (top of image) and the nuclei of CN XII (medial) and CN X (lateral). [[LFB stain|H&E-LFB stain]].
</gallery>

==References==
{{Gray's}}
{{Reflist}}
*{{cite book | title = Being and Perceiving | author = Haycock DE | publisher = Manupod Press | year = 2011 | isbn = 978-0-9569621-0-2 | url = https://books.google.com/books?id=fXFeQb1z6bsC |ref=refHaycockDE}}

==External links==
{{Commons category}}
* {{BrainMaps|medulla}}

{{Nervous system|state=expand}}
{{Rhombencephalon}}

{{Portal bar|Anatomy}}
{{Authority control}}

{{DEFAULTSORT:Medulla Oblongata}}
[[Category:Medulla oblongata| ]]