Question

Consider the following statements with two blanks X and Y and select the option which correctly fills up these blanks? In the center of the intervertebral disc, a soft area is present called ______ X __________. Which is supposed to be remnant of ________ Y _________.

X	Y
Nucleus pulposus	Notochord
Nerve cord	Notochord
Pulposus	Notochord
Notochord	Nerve cord

a. A
b. B
c. C
d. D

Answer 1

Hint: A gel like substance is found in the center of the intervertebral disc, which is known as nucleus pulposus. Nucleus pulposus is mainly made up of water and loose network of collagen fibers. This elastic structure allows the vertebral disc to withstand forces of compression and torsion.

Complete answer:
Vertebral column or spinal column is the central axis of the skeleton and is found in all vertebrates. It is made up of 23 vertebral discs. The intervertebral disc lies adjacent to each other in the vertebral column by a fibrous-cartilaginous joint. They function as shock absorbers. Intervertebral discs are composed of an annulus fibrosus and a nucleus pulposus.

- Annulus fibrosus is a radial structure made up of lamellae.
- Annulus fibrosus is present in the periphery with nucleus pulposus in the center. Nucleus pulposus is a gel-like substance which is found in the centre of the intervertebral disc.
- Nucleus pulposus is mainly made up of water and loose network of collagen fibers. This elastic structure allows the vertebral disc to withstand forces of compression and torsion. This nucleus pulposus is remnant of notochord in most vertebrates.
- The notochord is a flexible elongated cartilaginous structure found in embryonic stages and in some adult chordates. The main function of notochord is signaling and coordination of development.
- Notochord is only found in phylum chordata. In some animals, like the lamprey and the sturgeon, the notochord persists throughout life and in some vertebrates, like humans, a more complex backbone appears with some remnant of notochord. The remnant of the notochord is the nucleus pulposus.
- So, in the center of the intervertebral disc, a soft area is present called nucleus pulposus. Which is supposed to be remnant of notochord

Hence, the correct answer is option (A).

Note: Notochord is different from nerve cord. Notochord is a skeletal rod, and the nerve cord is made up of a solid strand of nervous tissue. The notochord belongs to the skeleton and the nerve cord belongs to the central nervous system.