Structure of Human Spermatozoan

The mature human sperm is a microscopic, flagellated, motile gamete, its entire body wrapped in a single plasma membrane and organised into three main regions: head, neck and tail. The head carries two components — a flat, oval nucleus, and, capping its tip, the acrosome, a small pointed structure formed mainly from the spermatid's Golgi body. The acrosome is packed with the enzyme hyaluronidase (popularly called sperm lysin), which the sperm uses to digest a path through the ovum's coats during fertilisation. The neck is very short, sitting between the head and the middle piece, and contains a proximal centriole (which later plays a role in the zygote's first cell division) and a distal centriole, which gives rise to the axial filament running the length of the tail. In the middle piece, mitochondria are wound tightly around this axial filament in what is called the mitochondrial spiral or nebenkern, generating the ATP that powers the sperm's movement. The tail, the longest part of the whole sperm, is slender and tapering, built around a central axial filament (axoneme) sheathed in cytoplasm; its lashing, whip-like movements are what push the sperm forward. A single ejaculation delivers roughly 200-300 million sperm, of which at least 60% should have a n …