ABSTRACT
Mammalian spermatozoa are composed of a head and a tail region. The head, surrounded by a plasma membrane, contains the apical acrosome (enlarged lysosome with outer and inner acrosomal membrane), nucleus (haploid complement of genomic DNA bound to sperm-specific histones), and postnuclear cap. The tail region includes the midpiece (densely packed, helical array of mitochondria that produce ATP), principal piece (self-powered flagellum with 9 + 2 array of microtubules), and terminal piece. Freshly ejaculated mammalian sperm are incapable of fertilizing ova but acquire functional competence through capacitation. Only capacitated sperm can penetrate the cumulus oophorus, bind to the ZP, and undergo the acrosome reaction.
