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. In lower vertebrates, it persists throughout life as the main axial support of the body, while in higher vertebrates it is replaced by the vertebral column. The notochord is found on the ventral surface of the neural tube. Image File history File links Image19. ... This article or section is in need of attention from an expert on the subject. ... Chordamesoderm is a type of mesoderm that lies along the central axis, under the neural tube. ... This article or section is in need of attention from an expert on the subject. ... Nucleus pulposus is the jelly-like substance in the middle of the spinal disc. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo. ... For other uses, see Embryo (disambiguation). ... Typical Classes See below Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... For other uses, see Embryo (disambiguation). ... This article does not cite any references or sources. ... diagram of the axial skeleton The axial skeleton consists of the 80 bones in the head and trunk of the human body. ... The vertebral column seen from the side Different regions (curvatures) of the vertebral column The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen. ... In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. ... In the developing vertebrate nervous system, the neural tube is the precursor of the central nervous system, which comprises the brain and spinal cord. ...

Notochords were the first "backbones", as well, serving as support structures in chordates that lacked a bony skeleton. The very first vertebrates, such as Haikouicthys, had only a notochord. Embryos of vertebrates have notochords today, as embryonic development often happens to follow a pattern similar to the ancestral evolution of the modern animal's traits [this idea that 'ontogeny recapitulates phylogeny' is something of an old-fashioned concept in embryology]. Notochords were advantageous to primitive fish-ancestors because they were a rigid structure for muscle attachment, yet flexible enough to allow more movement than, for example, the exoskeleton of the dominant animals of that time. In humans, they eventually develop into the disks between the vertebrae. Hakouicthys was an early craniate. ...

Development

Notogenesis is the development of the notochord by the epiblasts that make up the floor of the amnion cavity (Human Embryology). The notochord arises as a pouch from the mesoderm. In embryology, the epiblast is a feature present during gastrulation. ... For the alien race in Stephen Donaldsons The Gap Cycle, see Amnion (Gap Cycle). ...

The notochord forms during gastrulation and soon after induces the formation of the neural plate (neurulation), synchronizing the development of the neural tube. On the ventral aspect of the neural groove an axial thickening of the endoderm takes place. (In bi-pedal chordates, e.g. humans, this surface is properly referred to as the anterior surface). This thickening appears as a furrow (the chordal furrow) the margins of which anastimose (come into contact), and so convert it into a solid rod of polygonal-shaped cells (the notochord) which is then separated from the endoderm. It has been suggested that epiboly be merged into this article or section. ... The neural plate is thick and flat bundle of ectoderm which develops in the embryo into the nervous system. ... Neurulation is a part of organogenesis in vertebrate embryos. ... In the developing vertebrate nervous system, the neural tube is the precursor of the central nervous system, which comprises the brain and spinal cord. ... In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. ... Organs derived from each germ layer. ... In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. ...

In higher vertebrates, it extends throughout the entire length of the future vertebral column, and reaches as far as the anterior end of the midbrain, where it ends in a hook-like extremity in the region of the future dorsum sellæ of the sphenoid bone. Initially it exists between the neural tube and the endoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medially and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull, vertebral column, and the membranes of the brain and medulla spinalis are developed. In biological anatomy, the mesencephalon (or midbrain) is the middle of three vesicles that arise from the neural tube that forms the brain of developing animals. ... The sphenoid bone (from Greek sphenoeides, wedgelike) is a bone situated at the base of the skull in front of the temporals and basilar part of the occipital. ... Organs derived from each germ layer. ... For other uses of Skull, see Skull (disambiguation). ... The meninges (singular meninx) are the system of membranes that envelop the central nervous system. ... For other uses, see Brain (disambiguation). ... The spinal cord is a part of the vertebrate nervous system that is enclosed in and protected by the vertebral column (it passes through the spinal canal). ...

Postembryonic vestige of the notochord is found in the nucleus pulposus of the intervertebral disks, but not in the vertebral bodies, from which notochordal cells usually regress entirely. In humans, by the age of 4, all notochord residue is replaced by a population of chondrocyte-like cells of unclear origin^[1]. Persistence of notochordal cells within the vertebra may cause a pathologic condition- persistent notochordal canal^[2]. They are also found to persist in the nasopharyngeal space and, in such an unusual instance, may give rise to Tornwaldt's cyst. Nucleus pulposus is the jelly-like substance in the middle of the spinal disc. ... A diagram of a thoracic vertebra. ... Chondrocytes (< Greek chondros cartilage + kytos cell) are the only cells found in cartilage. ... Congenital vertebral anomalies are a collection of malformations of the spine in animals. ...

Research

Research into the notochord has played a key role in understanding the development of the central nervous system. By transplanting and expressing a second notochord near the dorsal neural tube, 180 degrees opposite of the normal notochord location, one can induce the formation of motoneurons in the dorsal tube. Motoneuron formation generally occurs in the ventral neural tube, while the dorsal tube generally forms sensory cells. A diagram showing the CNS: 1. ... In sciences dealing with the anatomy of animals, precise anatomical terms of location are necessary for a variety of reasons. ... This article describes the unit of angle. ... In vertebrates, motoneurons (also called motor neurons) are efferent neurons that originate in the spinal cord and synapse with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the...

The notochord secretes a protein called sonic hedgehog homolog (SHH), a key morphogen regulating organogenesis and having a critical role in signaling the development of motoneurons^[3]. The secretion of SHH by the notochord establishes the ventral pole of the dorsal-ventral axis in the developing embryo. Sonic hedgehog homolog (SHH) is one of three proteins in the mammalian hedgehog family, the others being desert hedgehog (DHH) and Indian hedgehog (IHH). ... A morphogen is a substance governing the pattern of tissue development and, in particular, the positions of the various specialized cell types within a tissue. ... Organogenesis is a stage of animal development where the ectoderm, endoderm, and mesoderm are formed. ...

Additional images

Surface view of embryo of Concolor gibbon (Hylobates concolor). Image File history File links Gray14. ... Binomial name (Harlan, 1826) Subspecies Nomascus concolor concolor Nomascus concolor lu Nomascus concolor jingdongensis Nomascus concolor furvogaster The Black Crested Gibbon (Nomascus concolor)[3], also known as the Crested Gibbon, the Black Gibbon, the White-cheeked Gibbon, or the Concolor Gibbon, is an endangered species of gibbon found in India...

Diagram of a transverse section, showing the mode of formation of the amnion in the chick. Image File history File links Gray29. ...

Section through the head of a human embryo, about twelve days old, in the region of the hind-brain. Image File history File links No higher resolution available. ...

Transverse section of human embryo eight and a half to nine weeks old. Image File history File links No higher resolution available. ...