[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [General embryology: weeks 1 to 8](https://durgical.com/en/embryology/#a-general) › Primitive streak and notochord (nucleus pulposus, sacrococcygeal teratoma) [Embryology](https://durgical.com/en/embryology/) · [General embryology: weeks 1 to 8](https://durgical.com/en/embryology/#a-general) # 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](https://durgical.com/en/anatomy/l4-l5/) · [L5–S1 disc](https://durgical.com/en/anatomy/l5-s1/) · [Sacrum](https://durgical.com/en/anatomy/sacrum/) · [Coccyx](https://durgical.com/en/anatomy/coccyx/) · [Spinal cord](https://durgical.com/en/anatomy/spinal-cord/) ## Key points - Adult remnant of the notochord: nucleus pulposus. - Primitive streak remnant: sacrococcygeal teratoma. - The notochord induces the neural plate (BMP antagonists) and the floor plate (SHH). - Chordoma: sacrum and clivus, TBXT (brachyury) gene. ## 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). ## Memory aid The notochord is the embryo's 'scaffolding': once the spine is built, all that is left of the scaffold is the soft filling of each disc. ## 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. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/primitive-streak-and-notochord/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [L4–L5 disc](https://durgical.com/en/anatomy/l4-l5/) - [L5–S1 disc](https://durgical.com/en/anatomy/l5-s1/) - [Sacrum](https://durgical.com/en/anatomy/sacrum/) - [Coccyx](https://durgical.com/en/anatomy/coccyx/) - [Spinal cord](https://durgical.com/en/anatomy/spinal-cord/) ## Related - [Week 3: gastrulation and the trilaminar disc](https://durgical.com/en/embryology/week-3-gastrulation-and-the-trilaminar-disc/) - [Neurulation and closure of the neural tube](https://durgical.com/en/embryology/neurulation-and-closure-of-the-neural-tube/) - [Paraxial mesoderm and somites: sclerotome, myotome, dermatome](https://durgical.com/en/embryology/paraxial-mesoderm-and-somites-sclerotome-myotome-dermatome/) - [Vertebrae: resegmentation of the sclerotomes](https://durgical.com/en/embryology/vertebrae-resegmentation-of-the-sclerotomes/) - [Molecular regulation: Shh, Wnt, FGF, BMP, Hox genes and retinoic acid](https://durgical.com/en/embryology/molecular-regulation-shh-wnt-fgf-bmp-hox-genes-and-retinoic-acid/) - [Germ-layer derivatives: ectoderm, mesoderm, endoderm](https://durgical.com/en/embryology/germ-layer-derivatives-ectoderm-mesoderm-endoderm/) ## Related conditions - [Lumbar Disc Herniation](https://durgical.com/en/conditions/lumbar-disc-herniation/) [← All of embryology](https://durgical.com/en/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](https://medlineplus.gov/genetics/condition/chordoma/) (MedlinePlus (U.S. National Library of Medicine), 2026); [Caudal regression syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/caudal-regression-syndrome/) (MedlinePlus (U.S. National Library of Medicine), 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/embryology/primitive-streak-and-notochord/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/primitive-streak-and-notochord/