Hyperactivation

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Hyperactivation is a special form of sperm movement. In this state, the sperm tail beats with larger, irregular waves, making the sperm swim faster and more forcefully.

This change helps the sperm get through the protective layers around the egg, especially the zona pellucida. It is driven by a rise of calcium inside the tail, which is controlled by CatSper channels. The extra calcium makes the tail bend more deeply and push the sperm forward.

Hyperactivation is part of sperm activation, the overall process that prepares a sperm to fertilize the egg. Activation can also include the acrosome reaction, where the cap on the head releases enzymes to help penetrate the egg.

Signals from the egg or surrounding cells can trigger activation. In the body, progesterone released by nearby cells and binding to the egg’s zona pellucida help start activation; in lab studies, calcium ionophores can also induce it.

Sperm that have not hyperactivated are often trapped in the lining of the fallopian tube. Only hyperactivated sperm can escape and fertilize the egg. Hyperactivation also helps guide sperm toward the egg in response to chemical signals (chemotaxis).

Note: the term hyperactivation is also used in genetics to describe a different phenomenon in Drosophila related to X chromosome gene activity; this is unrelated to sperm.