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Embryology · General embryology: weeks 1 to 8

Primitive streak and notochord (nucleus pulposus, sacrococcygeal teratoma) !

  • Embryonic structure

The notochord is a rod of cells in the embryo's midline that organizes the nervous system and spine; in adults it remains in the center of the discs.

Updated 2026-11-01

See it in 3D: L4–L5 disc · L5–S1 disc · Sacrum · Coccyx · Spinal cord

What it is

The notochord forms in week 3 from primitive node cells that advance cranially beneath the ectoderm. It is the embryo's axis: it induces the overlying ectoderm to become neural plate and, through SHH, shapes the ventral neural tube and the sclerotomes that build the vertebrae. It mostly disappears; its adult remnant is the nucleus pulposus of the intervertebral discs.

Key facts

  • Week 3: the notochordal process grows from the primitive node toward the prechordal plate.
  • It briefly merges with the endoderm (neurenteric canal) and then separates as a solid rod.
  • It induces the neural plate by blocking BMP signaling (noggin, chordin, follistatin).
  • Its SHH induces the floor plate of the neural tube and the sclerotome.
  • Where the vertebral body surrounds it, the notochord degenerates; between vertebrae it persists as the nucleus pulposus.
  • The primitive streak normally vanishes by the end of week 4; remnants can form a sacrococcygeal teratoma.

Structure

  • A cord of axial mesodermal cells in the midline, between the neural tube and the gut.
  • It runs from the prechordal plate (cranially) to the primitive node (caudally).

What it becomes

  • Nucleus pulposus of the intervertebral discs (the annulus fibrosus comes from sclerotome).
  • Axis organizer: neural plate, floor plate and the vertebrae around it.
  • Ectopic remnants can give chordomas, mainly in the sacrum and clivus.

Markers

  • SHH
  • Brachyury (TBXT)
  • Noggin
  • Chordin
  • Follistatin

Clinical notes

  • Sacrococcygeal teratoma: a sacral mass in the newborn or on prenatal ultrasound; more common in girls; contains all three germ layers.
  • Chordoma: a rare tumor of notochordal remnants, mainly in the sacrum and skull base; linked to the TBXT gene.
  • Disc herniation: the notochord-derived nucleus pulposus pushes out through the annulus fibrosus.
  • A faulty notochord or SHH signal is linked to midline defects (holoprosencephaly, abnormal vertebrae).

Test yourself

Think of the answer, then tap the question to see it.

Which adult structure is the remnant of the notochord?

The nucleus pulposus of the intervertebral discs.

Which newborn tumor comes from primitive streak remnants, and where does it appear?

Sacrococcygeal teratoma, in the sacral and coccygeal region.

Which notochord molecule induces the ventral neural tube and the sclerotome?

Sonic hedgehog (SHH).

How does the notochord induce the neural plate?

It secretes BMP inhibitors (noggin, chordin, follistatin); without BMP signaling, ectoderm becomes neural instead of epidermis.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Langman's Medical Embryology, 13th ed., ch. 5: Third Week of Development: Trilaminar Germ Disc (Wolters Kluwer, 2015); Chordoma: MedlinePlus Genetics (MedlinePlus (U.S. National Library of Medicine), 2026); Caudal regression syndrome: MedlinePlus Genetics (MedlinePlus (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.