Remnant of notochord is ?
**Core Concept**
The notochord is a precursor to the spinal cord and vertebral column in embryonic development. It is a flexible, rod-like structure formed from the mesoderm layer. During embryogenesis, the notochord degenerates and is replaced by the vertebral column, but remnants persist in the adult body.
**Why the Correct Answer is Right**
The notochordal remnant is the nucleus pulposus, the gelatinous center of the intervertebral discs. The nucleus pulposus is composed of notochordal cells, which are remnants of the embryonic notochord. These cells produce proteoglycans, which give the nucleus pulposus its characteristic gel-like consistency. The notochordal cells also produce growth factors that regulate the development and maintenance of the intervertebral discs.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the annulus fibrosus is the fibrous outer layer of the intervertebral disc, not the remnant of the notochord.
* **Option B:** This option is incorrect because the vertebral body is the main weight-bearing structure of the spine, but it is not a remnant of the notochord.
* **Option C:** This option is incorrect because the spinal cord is the continuation of the brain's central nervous system, but it is not a remnant of the notochord.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the nucleus pulposus, a remnant of the notochord, is composed of notochordal cells that produce proteoglycans, which give the intervertebral disc its characteristic gel-like consistency.
**Correct Answer:** D. Nucleus pulposus