It may be the single greatest character Woody Allen ever created. The reluctant sperm from All You Ever Wanted to Know About Sex about to be ejaculated into the great unknown. He worries about the futility of his existence and the role he's about to play. If it's a masturbatory ejaculation he could end up on the ceiling and what if it's a homosexual encounter? The very thought makes him shudder. The last we see of him is when he's rushing through the vas deferens with all the other sperm towards his uncertain fate.
Sperm don't have existential angst, which is probably just as well. If they had brains and self-awareness they might well be intimidated by the daunting task that lies before them. At stake is nothing less than the continuation of life itself. Every person and animal that has ever walked the Earth is the product of an incredible victory of one lone cell against almost impossible odds. I always thought it was the best argument against suicide. "Do you know what one of your father's sperm went through to make you you?! Apologize. Apologize now to that sperm for even thinking of offing yourself." Indeed, the biography of that lone sperm is one of the greatest stories never told. If Hollywood ever did a biopic, people would be cheering and weeping in their seats. They never will make it of course, because sperm are just, well... sperm. But then Spongebob Squarepants is just a sponge and look how well he's done, so I guess you never know.
If Hollywood ever does film the life story of Mr. Sperm it would start in the testicles, specifically in the walls of the spaghetti-like seminiferous tubules which comprise the bulk of testicular tissue. The seminiferous tubules are essentially a sperm factory. The surfaces of these tubules are studded with special stem cells called germ cells that continually divide, creating daughter cells that themselves divide through the thick walls of the hollow tubules. Mr. Sperm's life begins at the final stage in germ cell division referred to as meiosis. His parent cell was a diploid with 46 chromosomes. That cell divided and created two haploid cells with 23 chromosomes each.
One of these chromosomes is the X chromosome and the cell that carries it would become a girl if she were to reach the egg first. But she won't because in our scenario that destiny belongs to the one with the Y chromosome, her brother and our hero – Mr. Sperm. It's an interesting - if somewhat useless - fact that if these two went on to impregnate twin eggs they would carry no common genes from the father's side. They would be half-twins. But the chances of this happening would be slim to none because these sperm are just two of about four hundred million that are ejaculated at any one time. That's a hundred million a spurt. It's an astounding number. Between five and ten thousand sperm are being formed 24/7 of a man's life after puberty. In the universe of potential people that could have been here instead of you, you are indeed the Chosen One.
How is it possible that so many sperm can be formed from two little gonads? Well two things really.
- Except for some hormone production, that's pretty much all your testicles do.
- Sperm are small. Really small. Imagine a man-sized Mr. Sperm (I'm thinking Pee Wee Herman should get the role). Starting with a medium close-up and executing a slow zoom out (Spielberg style), the camera would eventually frame a pair of testicles the size of greater London. And inside each ball is a labyrinth of these seminiferous tubules. Over a thousand in all, packed together like Ichiban noodles. Laid end to end the ones in your testicles exceed 600 meters. If your balls were the size of London they'd wrap twice around the equator.
Once meiosis is complete and each sperm cell (gamete) has a fixed and unique set of genetic instructions, the cell then has to undergo a transformation from a round cell to the elongated, flagellated, tadpoley sperm cell we all know and love. This is cell differentiation and in our analogy it corresponds to the fetal development of the sperm. Basically, the cell nucleus, Golgi apparatus and enzymes become the "head" region. The mitochondria concentrate in the midpiece which becomes the engine for the flagellum that develops from the cell's centrioles. It's a little known fact that the mature sperm utilizes nature's only known rotary-joint. The tail doesn't whip back and forth like a tail fin. It actually rotates, driving the sperm forward like a propeller.
Once Mr. Sperm has arrived at his essential form, he wiggles himself clear from the inner wall of the tubule and is swept into the center. Here he joins thousands of other newly hatched spermatozoa on a slow drift to the epididymis, a tightly coiled tube that lies on the posterior wall of the testes. The epididymis is a kind of nursery and finishing school for sperm. When Mr. Sperm arrives he's but a wee lad, full of fresh energy but lacking in maturity and purpose. He's unable to either swim forward (motility) or fertilize an egg. During his transit through the epididymis, Mr. Sperm is exposed to a bath of chemicals and sugars that nourish him and help him to mature.
As Mr. Sperm and the rest of his class approach graduation they enter a slightly enlarged area of the epididymis. This is the waiting room where we last saw Woody Allen. Just ahead of them, after a few more twists and hairpin turns, the epididymis turns into the vas deferens, a veritable autobahn for sperm. Unfortunately, the kids have no chance to exercise their new found motility. They're crammed in so tightly they can't swim. It's been ten weeks since the meiotic division that produced Mr. Sperm. He and his siblings are all reved up with no place to go. They must await the call.
But what if the call doesn't come? What if they happen to inhabit the body of a man who refuses to have sex or masturbate? If there is an emission omission, then the ending ain't a happy one. Mr. Sperm and the other members of his graduating class will die and ultimately be reabsorbed by the body. If ever there was an excuse for masturbation this is it! Better for sperm to end up on the ceiling than die a slow death in this cramped waiting room without a chance to even try out their tails.
But that's not going to happen to Mr. Sperm. Something is happening. Already some members of yesterday's class have left the waiting area carried by seminal fluids that have been building up for several minutes (pre-cum). When the signal finally comes down from the brain, by way of the sympathetic nervous system, things happen fast. The vas deferens contracts violently in a peristaltic action that sends Mr. Sperm and his buddies forward at blinding speed (around 23 miles per hour). Mr. Sperm barely has time to spin his flagellum in the vas deferens before they're joined by a tidal wave of prostatic fluid that drives them into the home stretch. The whole trip takes less than a second.
And when it's over Mr. Sperm finds himself not on the ceiling like so many of his brothers before him but deep inside a woman's vagina. It's mass confusion, but Mr. Sperm does what he was born to do. He swims forward. Less than a second later another blast propels more sperm past him but Mr. Sperm doesn't care. It's every sperm for his/herself. But lest you think it's just a gentlemanly race to the finish, think again. It's D-Day and Mr. Sperm and his comrades have just landed on the beaches of Normandy. In the next few days 500 million sperm will die, many violently... it's a battle for sperm supremacy and only one will succeed in his mission.
More next week...