Editing Concussion (section)

===Forces===
The [[human brain|brain]] is surrounded by [[cerebrospinal fluid]], which protects it from light trauma. More severe impacts, or the forces associated with rapid acceleration, may not be absorbed by this cushion.<ref name="Shaw02">
{{cite journal | vauthors = Shaw NA | title = The neurophysiology of concussion | journal = Progress in Neurobiology | volume = 67 | issue = 4 | pages = 281–344 | date = July 2002 | pmid = 12207973 | doi = 10.1016/S0301-0082(02)00018-7 | s2cid = 46514293 }}</ref> Concussions, and other [[Head injury|head-related injuries]], occur when external [[force]]s acting on the head are transferred to the [[brain]].<ref name="King_2014">{{cite journal | vauthors = King D, Brughelli M, Hume P, Gissane C | title = Assessment, management and knowledge of sport-related concussion: systematic review | journal = Sports Medicine | volume = 44 | issue = 4 | pages = 449–471 | date = April 2014 | pmid = 24403125 | doi = 10.1007/s40279-013-0134-x | s2cid = 207493127 }}</ref> Such [[force]]s can occur when the head is struck by an object or surface (a 'direct impact'), or when the [[torso]] rapidly changes position (i.e. from a [[Checking (ice hockey)#Body checking|body check]]) and force is transmitted to the head (an 'indirect impact').<ref name="King_2014" />

Forces may cause linear, rotational, or angular movement of the brain or a combination of them.<ref name=sivak/> In rotational movement, the head turns around its center of gravity, and in angular movement, it turns on an axis, not through its center of gravity.<ref name=sivak/> The amount of rotational force is thought to be the major component in concussion<ref name=Poirier/> and its severity.<ref name="AndersonT">{{cite journal |vauthors=Anderson T, Heitger M, Macleod AD |year=2006 |url=http://www.vanderveer.org.nz/research/publications/papers/0344.pdf |title=Concussion and mild head injury |journal=[[Practical Neurology]] |volume=6 |pages=342–57 |doi=10.1136/jnnp.2006.106583 |issue=6 |url-status=dead |archive-url=https://web.archive.org/web/20070701212002/http://www.vanderveer.org.nz/research/publications/papers/0344.pdf |archive-date=2007-07-01 |citeseerx=10.1.1.536.9655 |s2cid=73308864 }}</ref> 
As of 2007, studies with athletes have shown that the amount of force and the location of the impact are not necessarily correlated with the severity of the concussion or its symptoms, and have called into question the threshold for concussion previously thought to exist at around 70–75&nbsp;[[G-force|''g'']].<ref name="Guskiewicz">{{cite journal | vauthors = Guskiewicz KM, Mihalik JP, Shankar V, Marshall SW, Crowell DH, Oliaro SM, Ciocca MF, Hooker DN | display-authors = 6 | title = Measurement of head impacts in collegiate football players: relationship between head impact biomechanics and acute clinical outcome after concussion | journal = Neurosurgery | volume = 61 | issue = 6 | pages = 1244–52; discussion 1252–53 | date = December 2007 | pmid = 18162904 | doi = 10.1227/01.neu.0000306103.68635.1a | s2cid = 32598614 }}</ref><ref name="Gever07">{{cite web |url=http://www.medpagetoday.com/Neurology/GeneralNeurology/tb/7625 |title=Any football helmet hit can cause potential concussion |date=December 7, 2007 |author=Gever D |publisher=[[MedPage Today]] |access-date=2008-02-27 |archive-date=2008-05-17 |archive-url=https://web.archive.org/web/20080517055441/http://www.medpagetoday.com/Neurology/GeneralNeurology/tb/7625 |url-status=live }}</ref>

The parts of the brain most affected by rotational forces are the [[midbrain]] and [[diencephalon]].<ref name=Pearce/><ref name=NEJM2007/> It is thought that the forces from the injury disrupt the normal [[cell (biology)|cell]]ular activities in the [[reticular activating system]] located in these areas and that this disruption produces the loss of consciousness often seen in concussion.<ref name=NEJM2007/> Other areas of the brain that may be affected include the upper part of the [[brain stem]], the [[fornix of brain|fornix]], the [[corpus callosum]], the [[temporal lobe]], and the [[frontal lobe]].<ref name="biglered">{{cite journal | vauthors = Bigler ED | title = Neuropsychology and clinical neuroscience of persistent post-concussive syndrome | journal = Journal of the International Neuropsychological Society | volume = 14 | issue = 1 | pages = 1–22 | date = January 2008 | pmid = 18078527 | doi = 10.1017/S135561770808017X | doi-access = free }}</ref> [[Angular acceleration]]s of 4600, 5900, or 7900 [[radian|rad]]/s<sup>2</sup> are estimated to have 25, 50, or 80% risk of mTBI respectively.<ref>{{cite journal | vauthors = Rousseau P, Post A, Hoshizaki TB |title=The effects of impact management materials in ice hockey helmets on head injury criteria |journal=Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology |issn=1754-3371 |issue=4 |volume=223 |year=2009  |pages=159–65 |doi=10.1243/17543371JSET36 |s2cid=137153670 }}</ref>