What causes the sperm cell to move?

Overview

The male reproductive system creates sperm that is manufactured in the seminiferous tubules within each testicle. The head of the sperm contains the DNA, which when combined with the egg's DNA, will create a new individual. The tip of the sperm head is the portion called the acrosome, which enables the sperm to penetrate the egg. The midpiece contains the mitochondria which supplies the energy the tail needs to move. The tail moves with whip-like movements back and forth to propel the sperm towards the egg. The sperm have to reach the uterus and the fallopian tube in order to fertilize a woman's egg.

Updated by: John D. Jacobson, MD, Department of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

The rhythmic whipping of a sperm’s tail (flagella) as it strives to reach the egg for fertilization depends on the ability of calcium to enter the sperm cell. Up until now, the factor(s) involved in allowing for this calcium movement have been unknown.

A recent study, published in the journal Science, reveals several key regulatory steps that are involved in sperm motility. Progesterone plays several physiological roles with respect to sperm function. In fact, the inability of sperm cells to respond to progesterone has been linked to male infertility in vitro.

Progesterone is a female sex hormone that plays an important role in signaling to the sperm as they navigate the female reproductive tract. Progesterone is a steroid hormone  and thus can only be secreted by steroid glands such as the adrenal cortex, testes and ovaries (and the placenta during pregnancy). It is released by the ovaries and the cells that surround the oocyte (egg).

Steroids effect changes in a cell via two mechanisms. One is entering the nucleus of the cell, binding the DNA and resulting in gene expression. The other way in which a steroid (in this case progesterone) affects cellular changes occurs by binding to receptors on the sperm cell membrane – what is referred to as non-genomic or genome-independent, signaling. Many aspects of the latter method remain unknown and have yet to be elucidated.

In this particular study, researchers have discovered an enzyme, ABHD2, in sperm cells that is dependent on progesterone. When progesterone binds to its receptor on the sperm cell, ABHD2 causes breakdown of a key hormone, 2-arachidonlyglycerol or 2AG. 2AG acts like a gate that blocks calcium from entering the sperm cell, therefore, if you break down this gate, you would observe an increased influx of calcium via a calcium channel called CatSper, which results in sperm activation and motility – a process referred to as hyperactivation. The sperm are concomitantly primed for fusion with the oocyte via hyperactivation.

“This is an important advance in explaining how sperm become hypermotile in the female reproductive tract. Developing new compounds that block ABHD2 ultimately may yield new contraceptive methods to prevent sperm from reaching the egg,” according to Stuart Moss, PhD, director of the male reproductive health program at the National Institutes of Health’s (NIH) Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).

Sperm abnormalities account for 90 percent of cases of infertility in males which include either a low sperm count, decreased motility and abnormal shape. Hopefully, this will pave the road for successful fertility for these men or perhaps, potentially allow for men to take birth control pills – something many women would likely appreciate.

What is Sperm? A 101 Guide

Our guide to sperm will provide a technical explanation of what exactly sperm is, how it works, and debunk some common misconceptions about sperm.

When was the last time you thought about your sperm? For many people, the answer is effectively never, and that’s entirely normal. But understanding how sperm works is important, especially when trying to conceive. Healthy sperm are essential for having biological children, and is also an important marker of your overall health.

Table of contents:

What is sperm?

In the simplest of terms, sperm is the male sex cell or “gamete.” Sperm and egg cells are haploid, which means they carry half the amount of chromosomes that typical somatic (non-sex) cells do. A refresher from biology class: chromosomes are made up of DNA, which carries genetic information.

When a sperm cell combines with the egg, they join chromosomes, making a diploid organism with 46 chromosomes. (This process is known as “fertilization.”) This is why you inherit some traits from your father and some from your mother.

What does sperm look like?

Sperm cells are approximately 0.05 milliliters long (or about 2 thousandths of an inch). They’re not visible to the naked eye, but using a microscope, we can see the structure of sperm.

They have a few distinct parts: the head, which contains the nucleus where genetic material is carried; a midpiece; and a tail, which propels it for swimming and helps breach the egg.

Learn more about sperm anatomy.

What is sperm made of?

The head of the sperm is composed of a membrane, made of fatty acids, that houses the nucleus (full of genetic material) as well as cytoplasm, the salt/water/protein fluid that fills cells.

Additionally, at the tip of the head is the acrosome, a structure that’s bound to the sperm membrane in its own fatty acid layer and contains enzymes that allow the sperm to “digest” the outer layer of the egg for fertilization.

The midpiece or “neck” of a sperm contains mitochondria which generate the energy for the sperm’s activity, including the movement of its tail. The tail is made of protein fibers that contract to propel the sperm through the seminal fluid.

Are sperm alive?

That really depends on your definition of “alive.” Sperm cells have some characteristics of living organisms: they metabolize sugars to produce energy, they grow (mature), and they move on their own. However, they contain only half the genetic information of a complete cell; therefore, they can’t reproduce on their own.

Sperm have a limited “life span.” It takes approximately 70–90 days to produce and mature sperm in the testicles. If ejaculated into the female reproductive system, they live for about 5 days.

Outside the human body, sperm live a few seconds to a few hours, depending on the surface and temperature/humidity of the environment. If sperm are not ejaculated, they are eventually broken down and reabsorbed by the body.

How is sperm produced?

Sperm production, called spermatogenesis, begins at puberty, usually around age 12. Once sperm production starts, it will typically continue uninterrupted until death, though discernible defects in sperm quality and sperm quantity increase with age.

A healthy male reproductive system will produce around 50–100 million viable sperm each day. The whole process of spermatogenesis, from newly formed sperm to a fully mature one, usually takes around 74 days.

Spermatogenesis takes place in the testes, starting in vessels called “seminiferous tubules.” There, a germ cell (a “diploid” cell with 46 chromosomes) divides three times to produce multiple haploid spermatids (immature sperm). These divisions of the sperm cells create genetic variation. At this point, the sperm cells that have divided are still connected with cytoplasm.

In the next step, the spermatids begin to mature, a process driven by the male hormone testosterone. They form a tail and an acrosome, their DNA becomes more compact, and excess cytoplasm is removed to create individual structures.

At this point, sperm are still immotile (unable to move on their own). They are transported via muscle contractions to the epididymis, a coiled tube behind each testicle, where they mature further, gaining the ability to move on their own and fertilize an egg.

Relatively cool temperatures are important for spermatogenesis. That’s why, during puberty, the testicles descend from the body to hang between the legs. This keeps them about 4ºF cooler than the usual body temperature of 98.6ºF.

Where is sperm stored?

Once matured, sperm are stored within the epididymis, in a structure called the “cauda epididymis.” During ejaculation, they move via muscle contractions from this storage vessel to the vas deferens, which connects to the seminal vesicles, where seminal fluid is produced. Here, sperm mixes into the semen before moving to the urethra for ejaculation.

How do sperm fertilize an egg?

Fertilization is a “race to the top” of the female reproductive system, from the vagina to the fallopian tubes, where sperm meet the egg and fertilization occurs. On average, anywhere between 80 and 300 million sperm cells are released per ejaculation.

However, most are eliminated along the way; any abnormal or otherwise defective sperm fall to the many dangers of the journey, along with a good percentage of healthy sperm. In fact, less than 1 in a million from the original ejaculate will reach the egg at the time of fertilization.

The journey to the egg is complex, full of obstacles, and at times hostile. The acidic environment of the vagina will eliminate any sperm that linger for too long. Once sperm reach the cervix, they must navigate through a web of mucus that can trap many. A great deal of sperm can be lost to “crypts,” side-channels where they can survive for several days.

Once they reach the Fallopian tubes, many become bound to its surface; only a select few are freed and continue on to the egg — that is, if they’ve chosen the correct tube. It is hypothesized that this long, arduous journey is nature’s way of weeding out the weak, so only the healthiest, strongest sperm survive.

When a sperm reaches the upper part of the female reproductive system, it undergoes the final steps that allow it to fertilize the egg: chemical changes to the surface of the sperm allow the acrosome to access the egg and dissolve its outer layer, and the tail begins to “beat” faster to facilitate egg penetration.

What is sperm quality?

Sperm quality is assessed through three main parameters: motility, morphology, and genetic health. In addition to sperm quality, the quantity (count or concentration) of sperm is important for fertility, because so many sperm are lost during the journey through the female reproductive system. Learn more about sperm quality and sperm quality improvement.

Sperm quality testing

Sperm quality and quantity can both be determined via sperm testing, such as a semen analysis and/or a DNA fragmentation analysis.

A clinic-grade semen analysis is a great way to gain a deeper understanding of your sperm quality and overall fertility. Our at-home semen analyses provide a detailed overview about crucial sperm quality and male fertility factors, including volume, sperm count, sperm motility, sperm morphology, and sperm concentration. Our sperm quality test gives you all the tools you’ll need to optimize your fertility directly from your home.

Sperm quality testing is particularly important if you are trying to conceive, are looking to freeze your sperm, or simply want an accurate overview of your own fertility and overall health. Learn more about our at-home sperm quality testing options and sperm quality improvement.

Sperm freezing

Sperm freezing is one of the most effective ways to preserve your fertility and expand your family-building options.

Sperm freezing is a great option for people who may not be ready to have children just yet, but nonetheless would like to preserve sperm quality. Sperm freezing is also recommended if you are considering a vasectomy or will be undergoing treatment that may affect fertility, such as chemotherapy or gender-affirming hormone therapy.

With Legacy, you can freeze your sperm from the comfort of your own home with a simple mail-in semen collection kit. 

Learn more about sperm freezing.

References

Can sperm cells move on their own?

How do sperm move around?