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The notochord is an elastic, rod-like structure found in chordates. In chordate vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the vertebral column. In non-vertebrate chordates a notochord persists.
A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə).All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa.
The notochord plays an integral role in the development of the neural tube. Prior to neurulation, during the migration of epiblastic endoderm cells towards the hypoblastic endoderm, the notochordal process opens into an arch termed the notochordal plate and attaches overlying neuroepithelium of the neural plate. The notochordal plate then ...
Unlike other Cambrian animals, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail, but lacked jaws. [29] A vertebrate group of uncertain phylogeny, small eel-like conodonts , are known from microfossils of their paired tooth segments from the late Cambrian to the end of the ...
The ventral neural tube is patterned by sonic hedgehog (Shh) from the notochord, which acts as the inducing tissue. Notochord-derived Shh signals to the floor plate, and induces Shh expression in the floor plate. Floor plate-derived Shh subsequently signals to other cells in the neural tube, and is essential for proper specification of ventral ...
In the spinal cord, Shh is directed by both the notochord and floor plate regions which ultimately drives the organization of neural and glial progenitor populations. The specific glial populations impacted by Shh in these two regions include oligodendrocyte precursor cells (OPCs), oligodendrocytes , NG2+ cells, microglia , and astrocytes . [ 13 ]
The notochord was reinterpreted to run underneath the dorsal organ a thin rod-like filament. The body segments are anatomically blocks of skeletal muscles, called the myomeres, which are found in vertebrates only. No eyes can be observed. [24] The muscle orientation and flat shaped body indicate that Pikaia was an active and free swimmer. [8]
In higher vertebrates such as humans, the segmental plates are laid down during the process of gastrulation and the segmental plates appear on both sides of the mid-line neural epithelium. Later, the process of neurulation occurs in the mid-line and the segmental plates proceed to the side of the neural tube and notochord.