Notochord

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All are true about notochord except ?

A. Prenotochordal cells invaginating in the primitive pit move forward cephalad until they reach the prechordal plate.

B. The prechordal plate itself forms between the tip of the notochord and the buccopharyngeal membrane

C. Becomes annulus fibrosus of adult intervertebral disc

D. elongation of the notochord is a dynamic process

ANSWER:

Ans : C

Ref: Langman's Medical Embryology - 9th Edition

The notochord is a flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo.
Prenotochordal cells invaginating in the primitive pit move forward until they reach the prechordal plate.
The prechordal plate itself forms between the tip of the notochord and the buccopharyngeal membrane and is derived from some of the first cells that migrate through the node in a cephalic direction.
Although the notochord regresses entirely in the region of the vertebral bodies, it persists and enlarges in the region of the intervertebral disc. Here it contributes to the nucleus pulposus, which is later surrounded by circular fibers of the annulus fibrosus. Combined, these two structures form the intervertebral disc.
Because elongation of the notochord is a dynamic process, the cranial end forms first, and caudal regions are added as the primitive streak assumes a more caudal position.

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