Describe the ultra-structure of human sperm with the help of a labelled diagram.

Explanation

The human sperm is, a microscopic, long, flagellated and haploid motile cell and is formed of head, neck, middle piece and tail. (i) Head. It constitutes the anterior region of sperm containing nucleus and acrosome. The nucleus is a narrow, flat and oval structure consisting of densely packed nuclear chromatin material. The later is formed of and nucleo-protein. A small pointed sheathy acrosome is found at the anterior region of head and is derived from the golgi bodies. It contains hydrolytic enzyme hyalourinidase which helps the sperm to penetrate into ovum during fertilization by dispersing the cells of corona radiata. (ii) Neck. It is very short or indistinguishable region lying in between head and middle piece. It contains the proximal and distal centriole with 9+0 arrangement of microtubules. The proximal centriole forms the spindle in the first cleavage division of the fertilised ovum. The distal centriole gives rise to many fine micro- tubules which run upto sperm tail by passing through middle piece. (iii) Middle piece. It is a cylindrical region lying behind the neck. It contains number of mitochondrial spiral (nebenkern) which encircles the axial filament arising from distal centriole. The mitochondrial spiral contains the oxidative enzymes which provide energy for movement of sperm by the process called oxidative phosphorylation, (iv) Tail. It is the longest part of the sperm and is formed of main central axial filament and the outer protoplasmic sheath with small amount of cytoplasm. The axial filament is naked without any sheath at the porterior end called as end piece. The tail undulates rapidly, providing mobility to sperm in the fluid medium.