Human sperm consists of head, neck, middle piece and tail. Head consists of nucleus and chromosomes and is covered by acrosome which contains enzymes to penetrate the ovum. It releases acrosin which helps sperms to breaks through the zona pellucida of the ovum. The neck shows presence of proximal and distal centriole. Middle piece consists of mitochondria that are spirally arranged. These are known as Nebenkern. Tail consists of axial filament.