Editing Hyperactivation (section)

==Mechanisms==
Mammalian sperm cells become more active when they approach an egg cell in a process called '''sperm activation'''. Sperm activation has been shown to be caused by [[calcium]] [[ionophores]] ''in vitro'', [[progesterone]]<ref>{{Cite journal|last1=Miller|first1=Melissa R.|last2=Mannowetz|first2=Nadja|last3=Iavarone|first3=Anthony T.|last4=Safavi|first4=Rojin|last5=Gracheva|first5=Elena O.|last6=Smith|first6=James F.|last7=Hill|first7=Rose Z.|last8=Bautista|first8=Diana M.|last9=Kirichok|first9=Yuriy|last10=Lishko|first10=Polina V.|date=2016-04-29|title=Unconventional endocannabinoid signaling governs sperm activation via the sex hormone progesterone|journal=Science|language=en|volume=352|issue=6285|pages=555–559|doi=10.1126/science.aad6887|issn=0036-8075|pmid=26989199|pmc=5373689|bibcode=2016Sci...352..555M|doi-access=free}}</ref> released by nearby [[cumulus cells]] and binding to [[ZP3]] of the zona pellucida.

The initial change is called "hyperactivation", which causes a change in spermatozoa motility. They swim faster and their tail movements become more forceful and erratic.

A recent discovery links hyperactivation to a sudden influx of calcium ion into the tails.  The whip-like tail (flagellum) of the sperm is studded with [[ion channel]]s formed by proteins called [[CatSper]].<ref>{{Cite journal|last1=Miller|first1=Melissa R.|last2=Kenny|first2=Samuel J.|last3=Mannowetz|first3=Nadja|last4=Mansell|first4=Steven A.|last5=Wojcik|first5=Michal|last6=Mendoza|first6=Sarah|last7=Zucker|first7=Robert S.|last8=Xu|first8=Ke|last9=Lishko|first9=Polina V.|date=2018-09-04|title=Asymmetrically Positioned Flagellar Control Units Regulate Human Sperm Rotation|journal=Cell Reports|language=English|volume=24|issue=10|pages=2606–2613|doi=10.1016/j.celrep.2018.08.016|issn=2211-1247|pmid=30184496|pmc=6177234|doi-access=free}}</ref>  These channels are selective, allowing only calcium ion to pass.  The opening of CatSper channels is responsible for the influx of calcium.  The sudden rise in calcium levels causes the flagellum to form deeper bends, propelling the sperm more forcefully through the viscous environment.  Sperm hyperactivity is necessary for breaking through two physical barriers that protect the egg from fertilization.

Hyperactivation has also shown to serve as a feature of the human sperm [[chemotaxis]]. When the sperm is exposed to chemo-attractant, especially progesterone; the sperm will exhibit sudden flagellar arrest, followed by sharp turn and hyperactivation. This response suggests that hyperactivation serves as method to quickly guide sperm through chemo-attractant gradient.<ref>{{Cite journal|title = Behavioral Mechanism during Human Sperm Chemotaxis: Involvement of Hyperactivation|journal = PLOS ONE|date = 2011-12-07|pmc = 3233563|pmid = 22163296|pages = e28359|volume = 6|issue = 12|doi = 10.1371/journal.pone.0028359|first1 = Leah|last1 = Armon|first2 = Michael|last2 = Eisenbach|bibcode = 2011PLoSO...628359A|doi-access = free}}</ref>