High voltage electron microscopy of sperm axoneme

The axoneme of sea urchin spermatozoon has been examined in whole preparation by high voltage electron microscopy. Radial spokes appear arranged in triplets with intratriplet distance of 40 nm, distance between spoke 1 and 2 of 32 nm and between spoke 2 and 3 of 24 nm. Spoke 1 is thicker than others; the complex of the triplets around the 9 microtubule doublets forms a helix of 96 nm pitch. Nexin links connect the A tubule of a doublet with the B of the adjacent one, and also form a helix of 96 nm pitch.