Sperm capacitation is an interesting phenomenon in fertilization. Freshly ejaculated sperms are unable or poorly able to fertilize. Rather, they must first undergo a series of changes knlwn collecctively as capacitation. Capacitation is associated with removal of adherent seminal plasma proteins, reorgination of plasma membrane, lipids and proteins. It also seems to involve and influx of extracellular calcium, increase in cyclic AMP, and decrease in intracellular pH. The molecular details of capacitation appear to vary somewhat among species.
Capacitation occurs while sperm reside in the female reproductive tract for a period of time, as they normally do during gamete transport. The length of time required varies with species, but usually requires several hours. The sperm of many mammals, including humans, can also be capacitated by incubation in certain fertilisation media.
Sperm that have undergone capacitation are said to become hyperactivated, and among other things, display hyperactivated motility. Most importantly however, capacitation appears to destabilise the sperm’s membrane to prepare it for the acrosome reaction.