Sperm produced in the walls of the
seminiferous tubule in the
testis. The production of sperm is called
spermatogenesis. Men produce sperm from
puberty onwards, continuously. Each normal
ejaculation contains from 100 to 650 million sperm cells. A man can ejaculate daily with little loss of
fertilizing capability.
The
human sperm (along with many other species) is made of a
head,
middle piece and a
tail.
Head:
At the tip of the head is the acrosome (a special body containing enzymes), a nucleus(containing genetic information to pass on to the offspring) and a centriole. The shape varies form species to species, humans being an oval shape, while others are comma shaped or spherical.
Middle Piece:
Contains many mitochondria, or in other species a large single one. These provide the energy for the tail.
Note: The sperm mitochondria are not allowed into the egg upon fertilization, which is why mitochondrial inheritance is maternal.
Tail:
A long whip like structure, covered by a plasma membrane, used for transportation, by moving back and forth. Also called a flagellum.
Sperm determines the sex of the offspring, as it can contain either an X or Y chromosome.
What can kill sperm?
Intense or prolonged exposure to light. Notice that invitro fertilization labs (as shown on TV) usually have reduced light.
Acidic environments, like those found in the vagina. This is why ejaculate is basic, to help neutralize the deadly acid.
Heat. This is why the testes hang down from the body, to keep them cooler.
History:
It was once believed by sermists that ALL the heritable information was contained in the sperm. Shortly after the invention of the microscope (not a terribly powerful microscope), the spermists thought it had been proven once and for all. When they looked through the microscope at the sperms they saw a tiny little fetus in the head of each one.
Then the microscopes got more powerful...