[The movement of the human spermatozoon]

The human sperm flagellum is composed by an axoneme made up of peripheral doublets of longitudinal microtubules on which are fixed dynein arms and radial spokes. A mechanochemical cycle of attachment-detachment of dynein arms on the adjacent microtubules results in a sliding/bending or microtubules. This process repeated along the flagellum, induces the propagation of a wave. The progressive movement of ejaculated spermatozoa is modified during their transport through the feminal genital tract under the influence of microenvironmental factors. The microfibrillar structure of cervical mucus constraints the flagellar wave amplitude whereas the tubal or follicular secretions induce an hyperactivation of the movement characterized by a loss of progression and a high degree of flagellar curvature. Sperm movement modifications are depending on external regulatory factors among which some could be secreted by the oocyte or by the perioocyte layers to create a sperm chemotaxis which would optimize the gametic interaction. The external factors modulate sperm movement through their interaction with membrane "receptors" and intracellular messengers such as cyclic AMP, ATP, Calcium, pH. These latter control dynein-microtubules interaction through a phosphorylation-dephosphorylation process of axonemal proteins.