Notochord

The notochord is a flexible, rod-shaped support structure that develops along the body axis in chordates. It provides axial support and helps organize development of the nervous system and vertebral column.

Notochordal plate: A transient, flattened embryonic structure that forms as the notochord develops from the axial mesoderm. It is an intermediate stage in the formation of the notochord.
Chordate: An animal belonging to the phylum Chordata, whose members possess a notochord at some life stage. The notochord is one of the defining features of this animal group.
Amphioxus: A small marine cephalochordate that retains a notochord throughout life. Its persistent notochord illustrates the structure in a chordate without vertebrae.
Vertebra: An individual bone or cartilage element of the vertebral column. Vertebrae are segmented skeletal elements, unlike the notochord's continuous flexible rod.
Notochord sheath: A surrounding extracellular matrix layer that encloses and mechanically supports notochord cells. Its stiff outer layer helps the notochord resist compression while remaining flexible.
Axial mesoderm: Embryonic mesoderm located along the body axis that forms structures including the notochord. The notochord develops from this specialized midline tissue.
Tunicate: A marine invertebrate chordate whose larvae typically possess a notochord in the tail. The larval notochord shows that this structure can be restricted to an early life stage.
Hydrostatic skeleton: A support system in which fluid pressure within a body cavity works against surrounding muscles. It provides flexible support by fluid pressure rather than through a notochord's cellular rod.
Notochord vacuole: A fluid-filled space inside a notochord cell that contributes to cell rigidity and tissue mechanics. Vacuolated cells help make the rod an effective axial support.
Gastrulation: The embryonic process that reorganizes cells into germ layers and establishes the body plan. Gastrulation positions the cells that will form the notochord.

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