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{{Other uses}}
{{Use dmy dates|date=April 2017}}
{{Infobox brain
| Name = Pons
| Image = Brain bulbar region.svg
| Caption = Pons in the brainstem
| Image2 = Gray679.png
| Caption2 = [[Terms for anatomical ___location|Anteroinferior view]] of the [[medulla oblongata]] and pons
| IsPartOf = [[Brain stem]]
| Components =
| Artery = [[Pontine arteries]]
| Vein = Transverse and lateral pontine veins
}}
The '''pons''' (from [[Latin]] {{lang|la|pons}}, "bridge") is part of the [[brainstem]] that in [[human]]s and other [[Mammal|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 Varolius"), after the Italian anatomist and surgeon [[Costanzo Varolio]] (1543–75).<ref name="Gray1862">{{cite book| first=Henry | last=Gray|title=Anatomy, descriptive and surgical| url= https://books.google.com/books?id=btSyie_UtxAC&pg=PA514|access-date=10 November 2010| year=1862| publisher=Blanchard and Lea| pages= 514–}}</ref> This region of the brainstem includes [[neural pathways]] and [[nerve tract|tracts]] that conduct signals from the [[brain]] down to the cerebellum and medulla, and tracts that carry the sensory signals up into the [[thalamus]].<ref name="Saladin Kenneth S.2007">{{cite book | last= Saladin | first= Kenneth S. | year=
2007| title= Anatomy & physiology the unity of form and function| place= Dubuque, Iowa| publisher= McGraw-Hill| isbn= }}</ref>
== Structure ==
The pons in humans measures about {{convert|2.5|cm}} in length.<ref name="Saladin Kenneth S.2007" /> It is the part of the brainstem situated between the midbrain and the medulla oblongata.<ref name="Rahman2023" /><ref name="Sinnatamby-2011">{{Cite book |last=Sinnatamby |first=Chummy S. |title=Last's Anatomy |vauthors= |publisher= |year=2011 |isbn=978-0-7295-3752-0 |edition=12th |pages=478}}</ref> The horizontal ''medullopontine sulcus'' demarcates the boundary between the pons and medulla oblongata on the ventral aspect of the brainstem, and the roots of cranial nerves VI/VII/VIII emerge from the brainstem along this groove.<ref>{{Cite web |title=sulcus bulbopontis |url=https://medical-dictionary.thefreedictionary.com/sulcus+bulbopontis |access-date=2023-06-08 |website=TheFreeDictionary.com}}</ref> The junction of pons, medulla oblongata, and cerebellum forms the [[cerebellopontine angle]].<ref>{{Cite web |title=cerebellopontile angle |url=https://medical-dictionary.thefreedictionary.com/cerebellopontile+angle |access-date=2023-06-08 |website=TheFreeDictionary.com}}</ref> The ''superior pontine sulcus'' separates the pons from the midbrain.<ref name="Carpenter">{{cite book |last1=Carpenter |first1=M |title=Core text of neuroanatomy |date=1985 |publisher=Williams & Wilkins |isbn=0683014552 |page=42 |edition=3rd}}</ref> Posteriorly, the pons curves on either side into a [[middle cerebellar peduncle]].'''<ref name="Sinnatamby-2011" />'''
A [[transverse plane|cross-section]] of the pons divides it into a ventral and a dorsal area. The ventral pons is known as the [[basilar part of pons|basilar part]], and the dorsal pons is known as the [[pontine tegmentum]].<ref name="Rahman2023">{{cite web |last1=Rahman |first1=Masum |last2=Tadi |first2=Prasanna |title=Neuroanatomy, Pons |url=https://www.ncbi.nlm.nih.gov/books/NBK560589/ |website=StatPearls |publisher=StatPearls Publishing |access-date=11 August 2024 |date=2024}}</ref>
The ventral aspect of the pons faces the [[Clivus (anatomy)|clivus]], with the [[pontine cistern]] intervening between the two structures. The ventral surface of the pons features a midline [[basilar sulcus]] along which the [[basilar artery]] may or may not course. There is a bulge to either side of the basilar sulcus, created by the [[pontine nuclei]] that are interweaved amid the descending fibres within the substance of the pons. The [[superior cerebellar artery]] winds around the upper margin of the pons.'''<ref name="Sinnatamby-2011" />'''
=== Vasculature ===
Most of the pons is supplied by the [[pontine arteries]], which arise from the basilar artery. A smaller portion of the pons is supplied by the [[Anterior inferior cerebellar artery|anterior]] and [[posterior inferior cerebellar arteries]].
===Development===
During [[embryonic development]], the [[metencephalon]] develops from the [[rhombencephalon]] and gives rise to two structures: the pons and the cerebellum.<ref name="Saladin Kenneth S.2007"/> The [[alar plate]] produces sensory [[neuroblast]]s, which will give rise to the [[solitary nucleus]] and its [[special visceral afferent]] (SVA) column; the [[Cochlear nuclei|cochlear]] and [[vestibular nuclei]], which form the [[special somatic afferent]] (SSA) fibers of the [[vestibulocochlear nerve]], the spinal and principal [[trigeminal nerve nuclei]], which form the [[General somatic afferent fibers|general somatic afferent column]] (GSA) of the [[trigeminal nerve]], and the [[pontine nuclei]] which relays to the [[cerebellum]].
[[Basal plate (neural tube)|Basal plate]] neuroblasts give rise to the [[abducens nucleus]], which forms the [[general somatic efferent fibers]] (GSE); the facial and motor trigeminal nuclei, which form the [[special visceral efferent]] (SVE) column, and the [[superior salivatory nucleus]], which forms the [[general visceral efferent fibers]] (GVE) of the [[facial nerve]].
===Nuclei===
[[File:Lower pons horizontal KB.svg|thumb|300px|Cross-section of lower pons, axons shown in blue, grey matter in light grey. Anterior is down and posterior is up]]
A number of [[cranial nerve nuclei]] are present in the pons:
* mid-pons: the [[principal sensory nucleus of trigeminal nerve| principal sensory nucleus of the trigeminal nerve]] (V)
* mid-pons: the [[motor nucleus for the trigeminal nerve]] (V)
* lower down in the pons: [[abducens nucleus]] (VI)
* lower down in the pons: [[facial nerve nucleus]] (VII)
* lower down in the pons: [[Vestibulocochlear nerve|vestibulocochlear]] nuclei ([[vestibular nuclei]] and [[cochlear nuclei]]) (VIII)
==Function==
Functions of these four cranial nerves (V-VIII) include regulation of respiration, control of involuntary actions, sensory roles in hearing, equilibrium, and taste, and in facial sensations such as touch and pain, as well as motor roles in eye movement, facial expressions, chewing, swallowing, and the secretion of saliva and tears.<ref name="Saladin Kenneth S.2007"/>
The pons contains [[Nucleus (neuroanatomy)|nuclei]] that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.<ref name="Saladin Kenneth S.2007" />
Within the pons is the [[pneumotaxic center]] consisting of the [[subparabrachial nucleus|subparabrachial]] and the [[medial parabrachial nucleus|medial parabrachial]] [[nucleus (neuroanatomy)|nuclei]]. This center regulates the change from inhalation to exhalation.<ref name="Saladin Kenneth S.2007" />
The pons is implicated in [[sleep paralysis]], and may also play a role in generating dreams.<ref>{{cite web |last1=Koch |first1=Christof |title=Dream States: A Peek into Consciousness |url=https://www.scientificamerican.com/article/dream-states/ |website=Scientific American |publisher=Scientific American |access-date=17 September 2020}}</ref>
==Clinical significance==
* [[Central pontine myelinolysis]] is a [[demyelinating disease]] that causes difficulty with sense of balance, walking, sense of touch, swallowing and speaking. In a clinical setting, it is often associated with transplant or rapid correction of blood sodium. Undiagnosed, it can lead to death or [[locked-in syndrome]].
==Other animals==
===Evolution===
The pons first evolved as an offshoot of the medullary [[reticular formation]].<ref name=Pritchard>[[#refPritchard|Pritchard and Alloway ''Medical Neuroscience'']]</ref> Since [[lamprey]]s possess a pons, it has been argued that it must have evolved as a region distinct from the [[medulla oblongata|medulla]] by the time the first [[agnathans]] appeared, 525 million years ago.<ref name=Butler>[[#refButler|Butler and Hodos ''Comparative vertebrate neuroanatomy: evolution and adaptation'']]</ref>
==Additional images==
<gallery>
File:Pons.gif|Location and topography of pons (animation)
File:Gray701.png|Axial section of the pons, at its upper part
File:Gray719.png|Hind- and mid-brains; posterolateral view
File:Gray720.png|Median sagittal section of brain
File:Brain stem sagittal section.svg|Nuclei of the pons and brainstem
File:Slide2cuc.JPG|Cerebrum. Deep dissection. Inferior dissection.
</gallery>
==References==
{{Reflist|2}}
*{{cite book
| title = Medical neuroscience
|author1=Pritchard, TE |author2=Alloway, D
|name-list-style=amp | publisher = Hayes Barton Press
| year = 1999
| isbn = 978-1-59377-200-0
| url = https://books.google.com/books?id=m7Y80PcFHtsC
|ref=refPritchard}}
*{{cite book
| title = Comparative vertebrate neuroanatomy: evolution and adaptation
|author1=Butler, AB |author2=Hodos, W
|name-list-style=amp | publisher = Wiley-Blackwell
| year = 2005
| isbn = 978-0-471-21005-4
| url = https://books.google.com/books?id=3nO6ggvV1PUC&q=%22Comparative+vertebrate+neuroanatomy:+evolution+and+adaptation%22.
|ref=refButler}}
==External links==
{{Commons category|Pons}}
* [https://web.archive.org/web/20060502144925/http://faculty.ucc.edu/biology-potter/The_Brain/sld017.htm Diagram at UCC]
* {{BrainMaps|Pons}}
{{Nervous system}}
{{Pons}}
{{Authority control}}
[[Category:Pons| ]]
[[Category:Neurology]]
[[Category:Brain]]
[[Category:Brainstem]]
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