New research challenges more than three centuries of sperm movement theories. Human sperm appears to swim like wiggling eels under a microscope, tails gyrating to and fro as they seek an egg to fertilize. But do you know how sperm move?
For 350 years, sperms were thought to move by wiggling their tails like eels. However, studies show that they roll forward like a spinning top.
Swimming Inside a Human Body
Antonie van Leeuwenhoek, a Dutch scientist known as the father of microbiology, was the first to observe human sperm up close. Van Leeuwenhoek used his newly developed microscope to examine his sperm in 1677, discovering that the fluid was filled with tiny, wiggling cells for the first time.
A 2D microscope revealed that the sperm were propelled by tails that wiggled side to side as the sperm head rotated. This was understanding how human sperm moved for the next 343 years.
Many scientists have postulated that there is likely to be a very important 3D element to how the sperm tail moves, but to date we have not had the technology to reliably make such measurements.Allan Pacey, Professor of Andrology at the University of Sheffield in England
Gadêlha and his colleagues at the Universidad Nacional Autónoma de México began the research with “blue-sky exploration,” according to Gadêlha. They captured human sperm swimming on a microscope slide using three-dimensional imaging techniques and a high-speed camera capable of capturing 55,000 frames per second.
What we found was something utterly surprising, because it completely broke with our belief system.Hermes Gadêlha, a mathematician at the University of Bristol in the UK
The sperm tails were not whipping side to side. They could only beat in one direction instead. To extract forward motion from this asymmetrical tail movement, the sperm head rotated jitterily at the same time as the tail rotated. The head and the tail rotation are two separate movements controlled by two different cellular mechanisms, according to Gadêlha. The result resembles a spinning otter or a rotating drill bit when they come together. The one-sided tail movement evens out over a 360-degree rotation, adding to forward propulsion.
The sperm is not even swimming, the sperm is drilling into the fluid.Hermes Gadêlha, a mathematician at the University of Bristol in the UK
(Source: Live Science)
Technically, how the sperm moves is known as precession, which means that it rotates around an axis, but that axis of rotation is changing. The planets do this as they revolve around the sun, but a more familiar example is a spinning top, which wobbles and dances across the floor as it rotates on its tip.
It’s important to note that on their journey to the egg that sperm will swim through a much more complex environment than the drop of fluid in which they were observed for this study, In the woman’s body, they will have to swim in narrow channels of very sticky fluid in the cervix, walls of undulating cells in the fallopian tubes, as well have to cope with muscular contractions and fluid being pushed along (by the wafting tops of cells called cilia) in the opposite direction to where they want to go. However, if they are indeed able to drill their way forward, I can now see in much better clarity how sperm might cope with this assault course in order to reach the egg and be able to get inside it.Allan Pacey, Professor of Andrology at the University of Sheffield in England
Sperm motility, or the ability of sperm to move, is one of the critical metrics fertility doctors consider when assessing male fertility, according to Gadêlha. The rolling of the sperm’s head isn’t currently considered in any of these metrics, but further research may reveal certain defects that disrupt this rotation and thus stymie the sperm’s movement.
According to Pacey, fertility clinics use 2D microscopy, and more research is needed to determine whether 3D microscopy could benefit their analysis.
Certainly, any 3D approach would have to be quick, cheap and automated to have any clinical value, But regardless of this, this paper is certainly a step in the right direction.Hermes Gadêlha, a mathematician at the University of Bristol in the UK
(Source: Live Science)