Editing Brainstem (section)

==Structure==
The parts of the brainstem are the midbrain, the pons, and the medulla oblongata; the diencephalon is sometimes considered part of the brainstem.<ref name="Haines" />

The brainstem extends from just above the [[tentorial notch]] superiorly to the [[first cervical vertebra]] below the [[foramen magnum]] inferiorly.<ref name="Sinnatamby-2011">{{Cite book |last=Sinnatamby |first=Chummy S. |title=Last's Anatomy |publisher= Elsevier Australia|year=2011 |isbn=978-0-7295-3752-0 |edition=12th |pages=474}}</ref>

===Midbrain===
{{Main|Midbrain}}
[[File:Brainstem and thalamus ja ja 135.png|thumb|upright=1.4|Diagram showing the position of the colliculi. Superior shown in green and inferior in orange.]]
[[File:Midbrain-axial-showing-tectum-and-tegmentum.jpg|thumb|View of the midbrain showing covering tectum and tegmental floor]]
The [[midbrain]] is further subdivided into three parts: [[tectum]], [[tegmentum]], and the [[ventral tegmental area]].  The [[tectum]] forms the ceiling. The tectum comprises the paired structure of the [[superior colliculus|superior]] and [[inferior colliculus|inferior colliculi]] and is the dorsal covering of the [[cerebral aqueduct]]. The [[inferior colliculus]] is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei, as well as inputs from the auditory cortex. Its inferior brachium (arm-like process) reaches to the [[medial geniculate nucleus]] of the [[diencephalon]]. The [[superior colliculus]] is positioned above the inferior colliculus, and marks the rostral midbrain. It is involved in the special sense of vision and sends its superior brachium to the [[lateral geniculate body]] of the diencephalon.

The [[tegmentum]] which forms the floor of the midbrain, is ventral to the [[cerebral aqueduct]].  Several [[Nucleus (neuroanatomy)|nuclei]], [[neural tract|tracts]], and the [[reticular formation]] are contained here.

The [[ventral tegmental area]] (VTA) is composed of paired [[cerebral peduncle]]s. These transmit axons of [[upper motor neuron]]s.

====Midbrain nuclei====
The midbrain consists of:
*[[Periaqueductal gray]]:  The [[gray matter]] around the [[cerebral aqueduct]] contains neurons involved in the [[pain]] desensitization pathway.  Neurons synapse here. When stimulated by a signal, the synaptic connections activate neurons in the [[nucleus raphe magnus]]. The pathway then projects down into the [[posterior grey column]] of the spinal cord, inhibiting pain sensation transmission.
*[[Oculomotor nerve]] nucleus:  This is the third [[cranial nerve nucleus]].
*[[Trochlear nerve]] nucleus:  This is the fourth cranial nerve.
*[[Red nucleus]]: This is a motor nucleus that sends a descending tract to the [[lower motor neuron]]s.
*[[Substantia nigra pars compacta]]: This is a concentration of neurons in the ventral portion of the midbrain that uses [[dopamine]] as its [[neurotransmitter]] and is involved in both motor function and emotion. Its dysfunction is implicated in [[Parkinson's disease]].
*[[Reticular formation]]: This is a large area in the [[midbrain]] that is involved in various important functions of the midbrain. In particular, it contains lower motor neurons, is involved in the pain desensitization pathway, is involved in the arousal and consciousness systems, and contains the [[locus coeruleus]], which is involved in intensive [[alertness]] modulation and in [[Autonomic nervous system|autonomic]] reflexes.
*[[Central tegmental tract]]: Directly anterior to the floor of the [[fourth ventricle]], this is a pathway by which many tracts project up to the cortex and down to the spinal cord.
*[[Ventral tegmental area]]: A [[dopaminergic]] [[nucleus (neuroanatomy)|nucleus]], known as [[Dopaminergic cell groups#Cell group A10|group A10 cells]]<ref name="Hegarty">{{cite journal |last1=Hegarty |first1=SV |last2=Sullivan |first2=AM |last3=O'Keeffe |first3=GW |title=Midbrain dopaminergic neurons: a review of the molecular circuitry that regulates their development. |journal=Developmental Biology |date=15 July 2013 |volume=379 |issue=2 |pages=123–38 |doi=10.1016/j.ydbio.2013.04.014 |pmid=23603197|doi-access=free }}</ref> is located close to the midline on the floor of the midbrain.
*[[Rostromedial tegmental nucleus]]: A [[GABAergic]] nucleus located adjacent to the ventral tegmental area.

<gallery>

Midbrain - superior colliculus.svg|Cross-section of the midbrain at the level of the superior colliculus
Midbrain - inferior colliculus.svg|Cross-section of the midbrain at the level of the inferior colliculus
</gallery>

===Pons===
{{Main|Pons}}
{{expand section|date=April 2014}}
The pons lies between the midbrain and the [[medulla oblongata]]. It is separated from the midbrain by the [[superior pontine sulcus]], and from the medulla by the [[inferior pontine sulcus]].<ref name="Carpenter">{{cite book |last1=Carpenter |first1=Malcolm |title=Core text of neuroanatomy |date=1985 |publisher=Williams & Wilkins |isbn=0683014552 |pages=42–43 |edition=3rd}}</ref> It contains tracts that carry signals from the [[cerebrum]] to the medulla and to the [[cerebellum]] and also tracts that carry sensory signals to the [[thalamus]]. The pons is connected to the cerebellum by the [[cerebellar peduncles]]. The pons houses the respiratory [[pneumotaxic center]] and [[apneustic center]] that make up the pontine respiratory group in the [[respiratory center]]. The pons co-ordinates activities of the [[Cerebellum|cerebellar hemispheres]].<ref>{{Cite book |title=Discovering the Brain |last= Ackerman| first= Sandra |chapter=Major Structures and Functions of the Brain |year=1992 |publisher= National Academies Press|location= Washington (DC)|doi= 10.17226/1785 |pmid= 25121239|isbn= 978-0-309-04529-2|url=https://www.ncbi.nlm.nih.gov/books/NBK234157/}}</ref>
The [[pons]] and [[medulla oblongata]] are parts of the [[hindbrain]] that form much of the brainstem.

<gallery>

Pons - Middle.svg|Cross-section of the middle pons (at the level of cranial nerve V)
Pons - Inferior.svg|Cross-section of the inferior pons (at the level of the facial genu)
</gallery>

===Medulla oblongata===
{{Main|Medulla oblongata}}
{{expand section|date=April 2014}}
The [[medulla oblongata]], often just referred to as the medulla, is the lower half of the brainstem continuous with the spinal cord. Its upper part is continuous with the pons.<ref name="Alberts">{{cite book|last1=Alberts|first1=Daniel|title=Dorland's Illustrated Medical Dictionary.|date=2012|publisher=Saunders/Elsevier|isbn=978-1-4160-6257-8|edition=32nd|location=Philadelphia, PA}}</ref>{{rp|1121}} The medulla contains the [[cardiovascular centre|cardiac]], dorsal and ventral [[respiratory group]]s, and [[vasomotor center|vasomotor]] centres, dealing with [[heart rate]], [[breathing]] and [[blood pressure]]. Another important medullary structure is the [[area postrema]] whose functions include the control of [[vomiting]].

<gallery>

Medulla - Rostral level cross section.svg|Cross-section of the rostral (superior) medulla
Medulla - Middle level cross section.svg|Cross-section of the middle medulla
Medulla - Inferior level cross section.svg|Cross-section of the inferior medulla
</gallery>

===Pontomedullary junction===
The pons meets the medulla at the pontomedullary junction.<ref name="Mercier">{{cite journal |last1=Mercier |first1=PH |last2=Brassier |first2=G |last3=Fournier |first3=HD |last4=Picquet |first4=J |last5=Papon |first5=X |last6=Lasjaunias |first6=P |title=Vascular microanatomy of the pontomedullary junction, posterior inferior cerebellar arteries, and the lateral spinal arteries. |journal=Interventional Neuroradiology |date=30 March 2008 |volume=14 |issue=1 |pages=49–58 |doi=10.1177/159101990801400107 |pmid=20557786|pmc=3313705 }}</ref> This region is supplied by the joining of the [[Basilar artery|basilar]], [[vertebral artery|vertebral arteries]]. The [[posterior inferior cerebellar artery]] also joins from which a large number of perforating arteries arise. Lateral spinal arteries also emerge to supply the posterior surface of the medulla oblongata.<ref name="Mercier"/>

===Appearance===
;From the front
[[File:Slide2RAFA.JPG|thumb|The appearance of a [[cadaver]]ic brainstem from the front, with major parts labelled]]

In the medial part of the [[Medulla oblongata|medulla]] is the [[anterior median fissure of the medulla oblongata|anterior median fissure]].  Moving laterally on each side are the [[medullary pyramids (brainstem)|medullary pyramids]].  The pyramids contain the fibers of the [[corticospinal]] tract (also called the pyramidal tract), or the upper motor neuronal axons as they head inferiorly to synapse on lower motor neuronal cell bodies within the [[anterior grey column]] of the [[spinal cord]].

The [[anterolateral sulcus of medulla|anterolateral sulcus]] is lateral to the pyramids.  Emerging from the anterolateral sulci are the CN XII ([[hypoglossal nerve]]) rootlets.  Lateral to these rootlets and the anterolateral sulci are the [[Olivary body|olives]].  The olives are swellings in the medulla containing underlying inferior nucleary nuclei<ref>{{Cite journal |last1=Ding |first1=Song-Lin |last2=Royall |first2=Joshua J. |last3=Sunkin |first3=Susan M. |last4=Ng |first4=Lydia |last5=Facer |first5=Benjamin A. C. |last6=Lesnar |first6=Phil |last7=Guillozet-Bongaarts |first7=Angie |last8=McMurray |first8=Bergen |last9=Szafer |first9=Aaron |last10=Dolbeare |first10=Tim A. |last11=Stevens |first11=Allison |last12=Tirrell |first12=Lee |last13=Benner |first13=Thomas |last14=Caldejon |first14=Shiella |last15=Dalley |first15=Rachel A. |date=2017-02-01 |title=Comprehensive cellular-resolution atlas of the adult human brain |journal=The Journal of Comparative Neurology |volume=525 |issue=2 |pages=407 |doi=10.1002/cne.24130 |issn=1096-9861 |pmc=6886049 |pmid=27917481}}</ref> (containing various nuclei and afferent fibers).  Lateral (and dorsal) to the olives are the rootlets for [[Cranial nerves|CN]] IX ([[glossopharyngeal]]), CN X ([[vagus]]) and CN XI ([[accessory nerve]]).  The pyramids end at the [[pons|pontine]] [[medulla oblongata|medulla]] junction, noted most obviously by the large [[basal pons]].  From this junction, CN VI ([[abducens nerve]]), CN VII ([[facial nerve]]) and CN VIII ([[vestibulocochlear nerve]]) emerge.  At the level of the midpons, CN V (the [[trigeminal nerve]]) emerges.  Cranial nerve III (the [[oculomotor nerve]]) emerges ventrally from the midbrain, while the CN IV (the [[trochlear nerve]]) emerges out from the dorsal aspect of the midbrain.

Between the two pyramids can be seen a [[decussation]] of fibers which marks the transition from the medulla to the spinal cord. The medulla is above the decussation and the spinal cord below.

;From behind
[[File:Slide4RAFA.JPG|thumb|The appearance of a [[cadaver]]ic brainstem from behind, with major parts labelled]]
The most medial part of the [[medulla oblongata|medulla]] is the [[posterior median sulcus of medulla oblongata|posterior median sulcus]].  Moving laterally on each side is the [[gracile fasciculus]], and lateral to that is the [[cuneate fasciculus]].  Superior to each of these, and directly inferior to the [[obex]], are the gracile and cuneate tubercles, respectively.  Underlying these are their respective nuclei.  The obex marks the end of the [[fourth ventricle]] and the beginning of the [[central canal]].  The posterior intermediate sulcus separates the gracile fasciculus from the cuneate fasciculus.  Lateral to the cuneate fasciculus is the [[lateral funiculus]].

Superior to the obex is the floor of the [[fourth ventricle]].  In the floor of the fourth ventricle, various nuclei can be visualized by the small bumps that they make in the overlying tissue.  In the midline and directly superior to the obex is the [[vagal trigone]] and superior to that it the [[hypoglossal trigone]].  Underlying each of these are motor nuclei for the respective cranial nerves.  Superior to these trigones are fibers running laterally in both directions.  These fibers are known collectively as the [[striae medullares]].  Continuing in a [[Anatomical terms of location#Directional terms|rostral]] direction, the large bumps are called the facial colliculi.  Each [[facial colliculus]], contrary to their names, do not contain the facial nerve nuclei.  Instead, they have facial nerve axons traversing superficial to underlying abducens (CN VI) nuclei.  Lateral to all these bumps previously discussed is an indented line, or [[sulcus (anatomy)|sulcus]] that runs rostrally, and is known as the [[sulcus limitans]].  This separates the medial motor neurons from the lateral sensory neurons.  Lateral to the sulcus limitans is the area of the [[vestibular system]], which is involved in special sensation.  Moving rostrally, the inferior, middle, and superior cerebellar peduncles are found connecting the midbrain to the cerebellum.  Directly rostral to the superior cerebellar peduncle, there is the superior medullary velum and then the two trochlear nerves.  This marks the end of the pons as the [[inferior colliculus]] is directly rostral and marks the caudal midbrain. Middle cerebellar peduncle is located inferior and lateral to the superior cerebellar peduncle, connecting pons to the cerebellum. Likewise, inferior cerebellar peduncle is found connecting the medulla oblongata to the cerebellum.

===Blood supply===
[[File:Blausen 0114 BrainstemAnatomy.png|thumb|The brainstem receives blood via the [[vertebral artery|vertebral arteries]], shown here.]]
The main supply of blood to the brainstem is provided by the [[basilar artery|basilar arteries]] and the [[vertebral artery|vertebral arteries]].<ref name="Purves" />{{rp|740}} It is important to note that there is a bit of variability in how these arteries connect and supply blood to the brain, such as where the arteries fuse or are reinforced. The variability that exists allows for syndromes to be introduced if certain vessels are excluded from where they should normally be. Syndromes can be in fragments or combinations depending on how the vessels are arranged and if the brain is getting adequate blood supply.<ref>{{Cite web |date=2015-07-21 |title=Brainstem Arteries |url=https://www.umassmed.edu/strokestop/modules/module-3-the-blood-supply-of-the-brain/vertebral-basilar/brainstem-arteries/ |access-date=2024-12-06 |website=UMass Chan Medical School |language=en}}</ref>

===Development===
The human brainstem emerges from two of the three [[brain vesicle|primary brain vesicles]] formed of the [[neural tube]].  The [[mesencephalon]] is the second of the three primary vesicles, and does not further differentiate into a [[brain vesicle|secondary brain vesicle]].  This will become the midbrain.  The third primary vesicle, the [[rhombencephalon]] (hindbrain) will further differentiate into two secondary vesicles, the [[metencephalon]] and the [[myelencephalon]].  The metencephalon will become the [[cerebellum]] and the pons.  The more caudal myelencephalon will become the [[medulla oblongata|medulla]].