Hyperactivation is a type of sperm
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...

Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...

. Hyperactivated sperm motility is characterised by a high amplitude, asymmetrical beating pattern of the sperm tail (flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...

). This type of motility may aid in sperm penetration of the zona pellucida
Zona pellucida
The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...

, which encloses the ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...


Hyperactivation could then be followed by the acrosome reaction
Acrosome reaction
During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg in order to fertilize it. Fusing to the egg usually causes little problem, whereas penetrating through the egg's hard shell can present more of a problem to the sperm...

 where the cap-like structure on the head of the cell releases the enzymes it contains. This facilitates the penetration of the ovum and fertilisation.

Some definitions consider sperm activation to consist of these two processes of hyperactivation and the acrosome reaction

Hyperactivation is a term also used to express an X chromosome gene dosage compensation mechanism and is seen in Drosophila. Here, a complex of proteins bind to the X-linked genes to effectively double their genetic activity. This allows males (XY) to have equal genetic activity as females (XX), whose X's are not hyperactivated.


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
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 ionophores in vitro, progesterone
Progesterone also known as P4 is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy and embryogenesis of humans and other species...

 released by nearby cumulus cells and binding to ZP3
Zona pellucida sperm-binding protein 3, also known as zona pellucida glycoprotein 3 or the sperm receptor, is a protein that in humans is encoded by the ZP3 gene...

 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
Ion channel
Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

s formed by proteins called CatSper. 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.
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