Cartoon depiction of a sperm cell along with some of the ion channels present in it
The spermatozoon is a highly unique and specialized cell. Here we explain all the basics of sperm cell anatomy for those who may not have a background in the subject along with images.
The head is where the nucleus of the cell is located. The appearance of the head varies with the species, but in humans, the side view (shown above) appears more pointed while the frontal view is rounder.
The acrosome is an organelle unique to sperm that covers the apical part of the head. Hydrolytic enzymes are contained in the acrosome, which are released during the acrosome reaction in order to break down the zona pellucida of the egg. Toxins that interfere with capacitation, such as DEHP, can result in an impaired capability to undergo the acrosome reaction.
Immediately after the neck is the midpiece, which is where the mitochondria of the cell are located. One of our research interests is the potential role of mitochondrial uncouplers for sperm as a contraceptive.
The appearance of a cross section through the flagellum differs between the principal piece and the midpiece. In the midpiece (shown above), there is a characteristic 9+2 pattern in the outer dense fibers (ODF) with a 4, 5 split. In the principal piece, two of the ODFs become the longitudinal columns, resulting in a characteristic 4, 3 split pattern. Towards the end of the tail, the ODFs are no longer present.
The principal piece is the part of the flagellum that comes after the midpiece and comprises most of the flagellum. CatSper and ABHD2 in this region are responsible for hyperactivation.
The cytoplasmic droplet is not present in all sperm cells, but it allows us to perform electrophysiology when present.
The neck is located between the head and the midpiece of the sperm cell.
Electron micrographs for the head, acrosome, midpiece, axoneme, and neck were taken by John Della Rosa. Other images are taken from papers by Miller et al.