EM 318 Spermatozoa

Spermatozoon

Scanning electron microscopy (SEM) of spermatozoa.

A spermatozoon (or sperm cell) is the male gamete that transfers the male's genetic material to the female's egg (oocyte) for fertilization. It is a motile cell with a tail-like flagellum (about 65 um long) designed for rapid and efficient motility.

• Head - flat, disc-shaped (5 µm long and 3 µm wide)
  • Nucleus (blue) - contains haploid genetic material (23 chromosomes in humans)
  • Acrosome (orange) - cap-like structure covering the anterior two-thirds of the nucleus
    • Contains digestive enzymes that help disperse the cells of the corona radiata and penetrate the zona pellucida during fertilization
  • Post-acrosome Segment (yellow) - posterior one-third of the nucleus not covered by the acrosome
• Neck (cyan) - short segment (about 1 µm in length) that contains the centrioles
• Tail - long flagellum that contains the axonemal complex that forms its core
  • Middle Piece (green) - initial region surrounded by a helical sheath of tightly packed mitochondria
  • Principal Piece (dark green) - makes up most of the length of the tail
  • End Piece (dark green) - narrowing segment that only contains the axoneme

The tail produces whip-like movements that propel spermatozoa through the female reproductive tract

Courtesy of Gary E. Olson, Department of Cell and Developmental Biology, Vanderbilt University, Nashville, Tennessee.