Editing Human brain (section)

=== Gross anatomy ===
{{See also|Evolution of the brain#Evolution of the human brain|Neuroscience of sex differences}}
The adult human brain weighs on average about {{convert|1.2-1.4|kg|abbr=on}} which is about 2% of the total body weight,<ref name=CarpenterCh1>{{cite book |title=Carpenter's Human Neuroanatomy |last1=Parent |first1=A. |last2=Carpenter |first2=M.B. |publisher=Williams & Wilkins |year=1995 |isbn=978-0-683-06752-1 |chapter=Ch. 1}}</ref><ref name="Bigos">{{cite book |last1=Bigos |first1=K.L. |last2=Hariri |first2=A. |last3=Weinberger |first3=D. |title=Neuroimaging Genetics: Principles and Practices |publisher=[[Oxford University Press]] |isbn=978-0-19-992022-8 |year=2015 |page=157 |url=https://books.google.com/books?id=TF_iCgAAQBAJ&pg=PA157}}</ref> with a volume of around 1260&nbsp;[[cubic centimetre|cm<sup>3</sup>]] in men and 1130&nbsp;cm<sup>3</sup> in women.<ref name=Cosgrove>{{cite journal |last1=Cosgrove |first1=K.P. |last2=Mazure |first2=C.M. |last3=Staley |first3=J.K. |title=Evolving knowledge of sex differences in brain structure, function, and chemistry |year=2007 |journal=Biol Psychiatry |volume=62 |pages=847–855 |pmid=17544382 |pmc=2711771 |doi=10.1016/j.biopsych.2007.03.001 |issue=8}}</ref> There is substantial individual variation,<ref name=Cosgrove/> with the standard [[reference range]] for men being {{convert|1180-1620|g|lb|abbr=on}}<ref name="MolinaDiMaio2012">{{cite journal|last1=Molina|first1=D. Kimberley|last2=DiMaio|first2=Vincent J.M.|title=Normal Organ Weights in Men|journal=The American Journal of Forensic Medicine and Pathology|volume=33|issue=4|year=2012|pages=368–372|issn=0195-7910|doi=10.1097/PAF.0b013e31823d29ad|pmid=22182984|s2cid=32174574}}</ref> and for women {{convert|1030-1400|g|lb|abbr=on}}.<ref name="MolinaDiMaio2015">{{cite journal|last1=Molina|first1=D. Kimberley|last2=DiMaio|first2=Vincent J. M.|title=Normal Organ Weights in Women|journal=The American Journal of Forensic Medicine and Pathology|volume=36|issue=3|year=2015|pages=182–187|issn=0195-7910|doi=10.1097/PAF.0000000000000175|pmid=26108038|s2cid=25319215}}</ref>

The [[cerebrum]], consisting of the [[cerebral hemisphere]]s, forms the largest part of the brain and overlies the other brain structures.{{sfn|Gray's Anatomy|2008|pp=227-9}} The outer region of the hemispheres, the [[cerebral cortex]], is [[grey matter]], consisting of [[Cerebral cortex#Layers|cortical layers]] of [[neuron]]s. Each hemisphere is divided into four main [[lobes of the brain|lobes]] – the [[frontal lobe]], [[parietal lobe]], [[temporal lobe]], and [[occipital lobe]].{{sfn|Gray's Anatomy|2008|pp=335-7}} Three other lobes are included by some sources which are a ''central lobe'', a [[limbic lobe]], and an [[Insular cortex|insular lobe]].<ref name="Ribas">{{cite journal |page=7 |pmid=20121437|year=2010|last1=Ribas|first1=G. C.|title=The cerebral sulci and gyri|journal=Neurosurgical Focus|volume=28|issue=2|doi=10.3171/2009.11.FOCUS09245|doi-access=free}}</ref> The central lobe comprises the [[precentral gyrus]] and the [[postcentral gyrus]] and is included since it forms a distinct functional role.<ref name="Ribas"/><ref name="Frigeri">{{cite journal |pmid=25555079|year=2015|last1=Frigeri|first1=T.|title=Microsurgical anatomy of the central lobe|journal=Journal of Neurosurgery|volume=122|issue=3|pages=483–98|last2=Paglioli|first2=E.|last3=De Oliveira|first3=E.|last4=Rhoton Jr|first4=A. L.|doi=10.3171/2014.11.JNS14315 }}</ref>

The [[brainstem]], resembling a stalk, attaches to and leaves the cerebrum at the start of the [[midbrain]] area. The brainstem includes the midbrain, the [[pons]], and the [[medulla oblongata]]. Behind the brainstem is the [[cerebellum]] ({{langx |la|little brain}}).{{sfn|Gray's Anatomy|2008|pp=227-9}}

The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called [[meninges]]. The membranes are the tough [[dura mater]]; the middle [[arachnoid mater]] and the more delicate inner [[pia mater]]. Between the arachnoid mater and the pia mater is the [[Meninges#Subarachnoid space|subarachnoid space]] and [[subarachnoid cisterns]], which contain the [[cerebrospinal fluid]].{{sfn|Purves|2012|p=724}} The outermost membrane of the cerebral cortex is the basement membrane of the pia mater called the [[glia limitans]] and is an important part of the [[blood–brain barrier]].<ref name="Anatomy and Ultrastructure">{{Cite book |last1=Cipolla |first1=M.J. |chapter=Anatomy and Ultrastructure |title=The Cerebral Circulation |via=NCBI Bookshelf |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK53086/#s2.2 |publisher=Morgan & Claypool Life Sciences |date=January 1, 2009 |url-status=live |archive-url=https://web.archive.org/web/20171001170945/https://www.ncbi.nlm.nih.gov/books/NBK53086/#s2.2 |archive-date=October 1, 2017  }}</ref> In 2023 a fourth meningeal membrane has been proposed known as the [[subarachnoid lymphatic-like membrane]].<ref name="Fluids barriers">{{cite journal |vauthors=Plá V, Bitsika S, Giannetto MJ, Ladron-de-Guevara A, Gahn-Martinez D, Mori Y, Nedergaard M, Møllgård K |title=Structural characterization of SLYM-a 4th meningeal membrane |journal=Fluids Barriers CNS |volume=20 |issue=1 |pages=93 |date=December 2023 |pmid=38098084 |pmc=10722698 |doi=10.1186/s12987-023-00500-w |doi-access=free |url=}}</ref><ref name="Neuhuber">{{cite journal |vauthors=Neuhuber W |title=An "outer subarachnoid space": fact or artifact? A commentary on "Structural characterization of SLYM- a 4th meningeal membrane" fluids and barriers of the CNS (2023) 20:93 by V. Plá et al |journal=Fluids Barriers CNS |volume=21 |issue=1 |pages=48 |date=June 2024 |pmid=38831302 |pmc=11149175 |doi=10.1186/s12987-024-00539-3 |doi-access=free |url=}}</ref> The living brain is very soft, having a gel-like consistency similar to soft tofu.<ref name="NPR">{{cite news |title=A Surgeon's-Eye View of the Brain |url=https://www.npr.org/templates/story/story.php?storyId=5396115 |website=NPR |series= Fresh Air |date=May 10, 2006 |url-status=live |archive-url=https://web.archive.org/web/20171107023155/http://www.npr.org/templates/story/story.php?storyId=5396115 |archive-date=November 7, 2017  }}</ref> The cortical layers of neurons constitute much of the cerebral [[grey matter]], while the deeper subcortical regions of [[myelin]]ated [[axon]]s, make up the [[white matter]].{{sfn|Gray's Anatomy|2008|pp=227-9}} The white matter of the brain makes up about half of the total brain volume.<ref name="Neuron">{{cite journal |last1=Sampaio-Baptista |first1=C |last2=Johansen-Berg |first2=H |title=White Matter Plasticity in the Adult Brain |doi-access=free |journal=Neuron |date=December 20, 2017 |volume=96 |issue=6 |pages=1239–1251 |doi=10.1016/j.neuron.2017.11.026 |pmid=29268094|pmc=5766826 }}</ref>
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<!-- Header -->| header_align      = center
| header            = Structural and functional areas of the human brain

<!--image 1-->| image1            = Sobo 1909 624.png
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| alt1              = A diagram showing various structures within the human brain
| caption1          = Human brain bisected in the [[sagittal plane]], showing the white matter of the corpus callosum

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| alt2              = A diagram of the functional areas of the human brain
| caption2          = Functional areas of the human brain. Dashed areas shown are commonly left hemisphere dominant.
}}

====Cerebrum====
{{Main|Cerebrum|Cerebral cortex}}
[[File:Gray726.png|thumb|Major gyri and sulci on the lateral surface of the cortex]]
[[File:Gehirn, medial - Lobi en.svg|thumb|Lobes of the brain]]

The cerebrum is the largest part of the brain and is divided into nearly [[Symmetry in biology#Bilateral symmetry|symmetrical]] left and right [[cerebral hemisphere|hemisphere]]s by a deep groove, the [[longitudinal fissure]].<ref name="Davey">{{cite book |author=Davey, G. |title=Applied Psychology |isbn=978-1-4443-3121-9 |publisher=[[John Wiley & Sons]] |year=2011 |page=153 |url=https://books.google.com/books?id=K1qq1SsgoxUC&pg=PA153}}</ref> Asymmetry between the lobes is noted as a [[Paleoneurobiology#Asymmetry|petalia]].<ref>{{cite journal|pmid=30601110|year=2019|last1=Arsava|first1=E. Y.|title=Occipital petalia as a predictive imaging sign for transverse sinus dominance|journal=Neurological Research|volume=41|issue=4|pages=306–311|last2=Arsava|first2=E. M.|last3=Oguz|first3=K. K.|last4=Topcuoglu|first4=M. A.|doi=10.1080/01616412.2018.1560643|s2cid=58546404}}</ref> The hemispheres are connected by five [[Commissural fiber#Structure|commissures]] that span the longitudinal fissure, the largest of these is the [[corpus callosum]].{{sfn|Gray's Anatomy|2008|pp=227-9}}
Each hemisphere is conventionally divided into four main [[lobes of the brain|lobes]]; the [[frontal lobe]], [[parietal lobe]], [[temporal lobe]], and [[occipital lobe]], named according to the [[skull |skull bones]] that overlie them.{{sfn|Gray's Anatomy|2008|pp=335-7}} Each lobe is associated with one or two specialised functions though there is some functional overlap between them.<ref name=Ackerman/> The surface of the brain is [[gyrification|folded]] into ridges ([[gyrus|gyri]]) and grooves ([[sulcus (neuroanatomy)|sulci]]), many of which are named, usually according to their position, such as the [[frontal gyrus]] of the frontal lobe or the [[central sulcus]] separating the central regions of the hemispheres. There are many small variations in the secondary and tertiary folds.{{sfn|Larsen|2001|pp=455–456}}

The outer part of the cerebrum is the [[cerebral cortex]], made up of [[grey matter]] arranged in layers. It is {{convert|2 |to |4 |mm}} thick, and deeply folded to give a convoluted appearance.<ref>{{cite book |last=Kandel |first=E.R. |author2=Schwartz, J.H. |author3=Jessel T.M. |title=Principles of Neural Science |year=2000 |publisher=McGraw-Hill Professional |isbn=978-0-8385-7701-1 |page=[https://archive.org/details/isbn_9780838577011/page/324 324] |url=https://archive.org/details/isbn_9780838577011/page/324 }}</ref> Beneath the cortex is the cerebral [[white matter]]. The largest part of the cerebral cortex is the [[neocortex]], which has six neuronal layers. The rest of the cortex is of [[allocortex]], which has three or four layers.{{sfn|Gray's Anatomy|2008|pp=227–9}}

The cortex is [[brain mapping|mapped]] by divisions into about fifty different functional areas known as [[Brodmann's areas]]. These areas are distinctly different when [[Histology|seen under a microscope]].{{sfn|Guyton & Hall|2011|p=574}} The cortex is divided into two main functional areas – a [[motor cortex]] and a [[sensory cortex]].{{sfn|Guyton & Hall|2011|p=667}} The [[primary motor cortex]], which sends axons down to [[motor neuron]]s in the brainstem and spinal cord, occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The [[primary sensory areas]] receive signals from the [[sensory nerve]]s and [[nerve tract|tracts]] by way of [[Thalamus#Thalamic nuclei|relay nuclei]] in the [[thalamus]]. Primary sensory areas include the [[visual cortex]] of the [[occipital lobe]], the [[auditory cortex]] in parts of the [[temporal lobe]] and [[insular cortex]], and the [[somatosensory cortex]] in the [[parietal lobe]]. The remaining parts of the cortex are called the [[association areas]]. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex [[cognition|cognitive processes]] of [[perception]], [[thought]], and [[decision-making]].<ref>Principles of Anatomy and Physiology 12th Edition – Tortora, p. 519.</ref> The main functions of the frontal lobe are to [[Attentional control|control attention]], abstract thinking, behaviour, problem-solving tasks, and physical reactions and personality.<ref name="Freberg">{{cite book |author=Freberg, L. |title=Discovering Biological Psychology |publisher=[[Cengage Learning]] |year=2009 |pages=44–46 |isbn=978-0-547-17779-3 |url=https://books.google.com/books?id=-zyTMXAjzQsC&pg=PA44}}</ref><ref name="Kolb">{{cite book |last1=Kolb |first1=B. |last2=Whishaw |first2=I. |title=Fundamentals of Human Neuropsychology |publisher=[[Macmillan Publishers|Macmillan]] |year=2009 |pages=73–75 |isbn=978-0-7167-9586-5 |url=https://books.google.com/books?id=z0DThNQqdL4C&pg=PA73}}</ref> The occipital lobe is the smallest lobe; its main functions are visual reception, visual-spatial processing, movement, and [[Color vision#Color in the human brain|colour recognition]].<ref name="Freberg"/><ref name="Kolb"/> There is a smaller occipital lobule in the lobe known as the [[cuneus]]. The temporal lobe controls [[Echoic memory|auditory]] and [[visual memory|visual memories]], [[Language processing in the brain|language]], and some hearing and speech.<ref name="Freberg"/>

[[File:Visible Human head slice.jpg|thumb|upright|Cortical folds and white matter in horizontal bisection of head]]

<!--Ventricles and subcortical detail is here.-->The cerebrum contains the [[ventricular system|ventricles]] where the cerebrospinal fluid is produced and circulated. Below the corpus callosum is the [[septum pellucidum]], a membrane that separates the [[lateral ventricles]]. Beneath the lateral ventricles is the [[thalamus]] and to the front and below is the [[hypothalamus]]. The hypothalamus leads on to the [[pituitary gland]]. At the back of the thalamus is the brainstem.{{sfn|Pocock|2006|p=64}}

The [[basal ganglia]], also called basal nuclei, are a set of structures deep within the hemispheres involved in behaviour and movement regulation.{{sfn|Purves|2012|p=399}} The largest component is the [[striatum]], others are the [[globus pallidus]], the [[substantia nigra]] and the [[subthalamic nucleus]].{{sfn|Purves|2012|p=399}} The striatum is divided into a ventral striatum, and dorsal striatum, subdivisions that are based upon function and connections. The ventral striatum consists of the [[nucleus accumbens]] and the [[olfactory tubercle]] whereas the dorsal striatum consists of the [[caudate nucleus]] and the [[putamen]]. The putamen and the globus pallidus lie separated from the lateral ventricles and thalamus by the [[internal capsule]], whereas the caudate nucleus stretches around and abuts the lateral ventricles on their outer sides.{{sfn|Gray's Anatomy|2008|pp=325-6}} At the deepest part of the [[lateral sulcus]] between the [[insular cortex]] and the striatum is a thin neuronal sheet called the [[claustrum]].<ref name="Goll">{{cite journal |last1=Goll |first1=Y. |last2=Atlan |first2=G. |last3=Citri |first3=A. |title=Attention: the claustrum |journal=Trends in Neurosciences |date=August 2015 |volume=38 |issue=8 |pages=486–95 |doi=10.1016/j.tins.2015.05.006 |pmid=26116988|s2cid=38353825 }}</ref>

Below and in front of the striatum are a number of [[basal forebrain]] structures. These include the [[nucleus basalis]], [[diagonal band of Broca]], [[substantia innominata]], and the [[medial septal nucleus]]. These structures are important in producing the [[neurotransmitter]], [[acetylcholine]], which is then distributed widely throughout the brain. The basal forebrain, in particular the nucleus basalis, is considered to be the major [[cholinergic]] output of the central nervous system to the striatum and neocortex.<ref name="Goard">{{cite journal |last1=Goard |first1=M. |last2=Dan |first2=Y. |title=Basal forebrain activation enhances cortical coding of natural scenes |journal=Nature Neuroscience |date=October 4, 2009 |volume=12 |issue=11 |pages=1444–1449 |doi=10.1038/nn.2402|pmid=19801988 |pmc=3576925 }}</ref>

====Cerebellum====
[[File:Sobo 1909 623.png|thumb|upright=1.25|Human brain viewed from below, showing cerebellum and brainstem]]
{{Main|Cerebellum}}

The cerebellum is divided into an [[anterior lobe of cerebellum|anterior lobe]], a [[posterior lobe of cerebellum|posterior lobe]], and the [[flocculonodular lobe]].{{sfn|Guyton & Hall|2011|p=699}} The anterior and posterior lobes are connected in the middle by the [[cerebellar vermis|vermis]].{{sfn|Gray's Anatomy|2008|p=298}} Compared to the cerebral cortex, the cerebellum has a much thinner outer cortex that is narrowly furrowed into numerous curved transverse fissures.{{sfn|Gray's Anatomy|2008|p=298}}
Viewed from underneath between the two lobes is the third lobe the flocculonodular lobe.<ref>{{cite book |last1=Netter |first1=F. |title=Atlas of Human Anatomy Including Student Consult Interactive Ancillaries and Guides. |date=2014 |publisher=W B Saunders Co |location=Philadelphia, Penn. |isbn=978-1-4557-0418-7 |page=114 |edition=6th}}</ref> The cerebellum rests at the back of the [[posterior cranial fossa|cranial cavity]], lying beneath the occipital lobes, and is separated from these by the [[cerebellar tentorium]], a sheet of fibre.{{sfn|Gray's Anatomy|2008|p=297}}

It is connected to the brainstem by three pairs of [[nerve tract]]s called [[cerebellar peduncle]]s. The [[superior cerebellar peduncle|superior pair]] connects to the midbrain; the [[middle cerebellar peduncle|middle pair]] connects to the medulla, and the [[inferior cerebellar peduncle|inferior pair]] connects to the pons.{{sfn|Gray's Anatomy|2008|p=298}} The cerebellum consists of an inner medulla of white matter and an outer cortex of richly folded grey matter.{{sfn|Gray's Anatomy|2008|p=297}} The cerebellum's anterior and posterior lobes appear to play a role in the coordination and smoothing of complex motor movements, and the flocculonodular lobe in the maintenance of [[Equilibrioception|balance]]{{sfn|Guyton & Hall|2011|pp=698–9}} although debate exists as to its cognitive, behavioural and motor functions.{{sfn|Squire|2013|pp=761–763}}

====Brainstem====
{{Main|Brainstem}}
The brainstem lies beneath the cerebrum and consists of the [[midbrain]], [[pons]] and [[medulla oblongata|medulla]]. It lies in the [[posterior cranial fossa|back part of the skull]], resting on the part of the [[base of the skull|base]] known as the [[clivus (anatomy)|clivus]], and ends at the [[foramen magnum]], a large [[:wikt:foramen|opening]] in the [[occipital bone]]. The brainstem continues below this as the [[spinal cord]],{{sfn|Gray's Anatomy|2008|p=275}} protected by the [[vertebral column]].

Ten of the twelve pairs of [[cranial nerve]]s{{efn|Specifically the [[oculomotor]], [[trochlear nerve]], [[trigeminal nerve]], [[abducens nerve]], [[facial nerve]], [[vestibulocochlear nerve]], [[glossopharyngeal nerve]], [[vagus nerve]], [[accessory nerve]] and [[hypoglossal nerve]]s.{{sfn|Gray's Anatomy|2008|p=275}}}} emerge directly from the brainstem.{{sfn|Gray's Anatomy|2008|p=275}} The brainstem also contains many [[cranial nerve nucleus|cranial nerve nuclei]] and [[nucleus (neuroanatomy)|nuclei]] of [[nerve|peripheral nerves]], as well as nuclei involved in the regulation of many essential processes including [[breathing]], control of eye movements and balance.{{sfn|Guyton & Hall|2011|p=691}}{{sfn|Gray's Anatomy|2008|p=275}} The [[reticular formation]], a network of nuclei of ill-defined formation, is present within and along the length of the brainstem.{{sfn|Gray's Anatomy|2008|p=275}} Many [[nerve tract]]s, which transmit information to and from the cerebral cortex to the rest of the body, pass through the brainstem.{{sfn|Gray's Anatomy|2008|p=275}}