Question

Nucleus pulposus represents
(a) Remains of the notochord
(b) Area of ossification
(c) Region of non- ossification
(d) Area resistant to frictional damage

Answer 1

This is present in each intervertebral disc of embryonic midline structure common to all members of the phylum Chordata and higher vertebrates the notochord exists transiently.

Complete answer:
The cells in the primitive streak multiply and pass cranially reaching up to the caudal margin of the prechordal plate. The cells undergo several stages of arrangement ending in the formation of a solid cord called the notochord which further gives rise to nucleus pulposus in the region of each invertebrate disc. The notochord provides skeleton support where in most vertebrates it is replaced by a joint skeleton. The remains of the notochord exist as disks between the vertebrates as nucleus pulposus.
The notochord lies between the primitive streak and the prechordal plate which passes through several stages that are as follows:
- Primitive node: Also known as a primitive knot or Henson’s node which is the thickened cranial end of the primitive streak.
- Blastopore: the central depression in the primitive knot
- Notochordal process: This is marked by the head process.
- Nucleus pulposus formation.
So, the correct answer is, ‘remains of the notochord.’

Note:
- In chordates embryos, all have a common skeleton structure called a notochord which is a flexible rod located between the digestive tube and nerve cord.
- During the development of notochord, the persistent roof of the notochordal canal becomes folded upon itself to form a definitive notochord.
- Neurulation is the process in which the neural tube formation takes place. The neural tube formation gives rise to the brain and spinal cord which extends from the prochordal plate to the primitive knot that arises from the ectoderm.