Mechanisms of
Sperm Motility:
Dr. Charles Lindemann
Dr. Lindemann's Fun Sperm Facts!
Sperm are wonderful little cells and they can be loads of fun! For your enjoyment we've compiled some amazing facts about them.

See our FAQ page for additional fun information

A Wonderous Tale of a Sperm Tail - Originally published in the Fall 2010 issue (Issue 19) of The Oakland Journal

 

The QUESTION most frequently asked to Dr. Lindemann via e-mail: How long can sperm live on environmental surfaces? ANSWER: They die as they dry out, so it depends on how quickly they dry. They also are killed by fresh water due to osmotic shock. Soap and detergents such as those used for laundering and hand washing also kill them, as these substances strip off the cell membrane of the sperm. Something to consider: They are the haploid half of your life cycle so be careful where you leave them.

Please note, while sperm are relatively easy to kill on environmental surfaces, do not try to use water or detergents to kill them in the vagina or female reproductive tract. The female tract and the jelly-like consistency of human semen protect them from mixing well with water once inside the female body. In addition, water and detergent can be harmful to the tissues. This is not a good birth control strategy!
  Animal

Average number of sperm per ejaculate (in millions)

  
  Mouse 50  
  Rat 58  
  Guinea Pig 80  
  Rabbit 280  
  Man 280  
  Sheep 1000  
  Cow 3000  
  Pig 8000  
       

Time between coitus and arrival of sperm in the Fallopian tube *
(In other words the amount of time it takes for sperm to get where they need to go)
  Animal Travel Time  
  Cow 2-3 Minutes  
  Rabbit A few minutes  
  Mouse 15 Minutes  
  Guinea Pig 15 Minutes  
  Sow (Pig) 15 Minutes  
  Rat 15-30 Minutes  
  Hamster 2-60 Minutes  
  Dog Minutes-Hours  
  Ewe (Sheep) 6 Minutes - 5 Hours  
  Woman 5 - 68 Minutes  
       
Average volume and content of human ejaculate#

The volume and content of the ejaculate depend on the length of time between ejaculations. The average volume of semen is 2.75 mililiters(ml), ranging from 2-6 ml, the higher volumes following periods of abstinence. An average human ejaculate contains about 180 million sperm (66 million/ml), but some ejaculates contain as many as 400 million sperm. Both quantity and quality of the sperm are important determinants of fertility. A man is considered clinically infertile if his sperm concentration falls below 20 million/ml semen. # (Just remember though- it only takes ONE to make a baby)

The average sperm count fell from 113 million sperm/ml of semen in 1940 to 66 million/ml in 1990. The volume of a single ejaculate has declined from 3.40 ml to 2.75 ml. This means that men on average are now ejaculating less than half the number of sperm as men did 50 yrs ago. A drop from more than 380 million sperm to about 180 million sperm per ejaculate. Furthermore, the number of motile sperm has also dipped. Importantly, the sperm count has not declined in the less polluted areas of the world during the same time period.#
       
  Animal Fertile Life of Sperm (hours)  
  Mouse 6  
  Rat 14  
  Guinea Pig 21-22  
  Human 24-48  
  Rabbit 30-32  
  Sheep 30-48  
  Cow 28-50  
  Horse 144  
  Bat 135 Days  
Motile (moving) sperm have been found in the human fallopian tube up to 85 hours after coitus, although the ability to fertilize an egg is usually lost before motility is lost.
Does size matter?^      
One would think that a big animal would have bigger gametes, but nothing could be further from the truth. The biggest sperm I have ever seen came from a fruit fly! The sperm of a fruit fly can be as long as the body of the male fly, about 1.1 mm. On the other hand, of the vast number of mammals humans have one of the smallest sperm cells, measuring only 40 microns long. Rats produce one of the largest sperm at 170 microns long. When we talk of mice and men we may be the bigger animals in the diploid phase of life, but it is the mice that have the bigger haploid phase of life with 80-micron long sperm.
How many is enough?^      
This question always comes up in regard to human fertility. If it takes only one sperm to fertilize and egg, why does a low sperm count make a man infertile? A fertile male human ejaculates between 2 and 5 mililiters(ml) of semen (on average about a teaspoon). In each ml there are normally about 100 million sperm. If the concentration falls below 20 million sperm per mililiter there is usually some trouble with fertility. Twenty million still seems to be a lot, so why the problem? Only a small fraction of the sperm deposited in the woman's vagina end up in the uterus. From those that make it to the uterus, only a small fraction of those find their way to the oviducts. Usually the egg is all the way up at the other end of the oviduct(fallopian tube). Of those that are in the oviduct only a small fraction make their way from the lower to the upper oviduct. So, in fact, the number of sperm successfully arriving at where the egg is located is actually very small. Another problem is that the egg is not just waiting to be fertilized by the first sperm to come along. The egg is usually covered by a thick layer of cells called the corona radiata that serve as a blockade to restrict sperm from getting into the egg. Sperm cells contain enzymes that break this barrier down. It may actually require an assault of many sperm to break down the corona sufficiently to let one sperm get through to the egg. So the whole process is somewhat like a marathon run in a maze filled with mucus followed by breaking into a fortress. That one sperm that finally makes it is the champion of Mother Nature's triathlon. If you don't have enough competitors to start, none are left at the finish. We don't know for sure but this may be a way of selecting for a healthy sperm to do the job of passing genes to the next generation. Modern in-vitro fertilization techniques can by-pass this selection process and achieve fertilization with much fewer sperm. Successful fertilization is now even accomplished with sperm that can't swim. This is accomplished by directly injecting sperm into the egg with a tiny glass pipette (tube). Only time will tell what bypassing nature's triathlon will do to the human gene pool.

* Austin and Short (1982) Reproduction in mammals: Germ cells and fertilization. Cambridge University Press, NY, NY

# Lauralee Sherwood (2001) Human Physiology: From cells to systems. Brooks/Cole, Pacific Grove, CA

^ Charles B. Lindemann

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