difference between notochord and nerve chord
NOTOCHORD - A flexible rodlike structure that forms the supporting axis of the body in the lowest chordates and lowest vertebrates and in embryos of higher vertebrates .
NERVE CHORD - there are 2 types of nerve chord,
- in invertebrates, it refers to the ventral nerve cord, whereas
- in chordates, it stands for the dorsal nerve cord.
The dorsal nerve cord is one of the embryonic features unique to chordates, along with a notochord, a post-anal tail and pharyngeal slits. The dorsal nerve cord is a hollow cord dorsal to the notochord.It is formed from a part of the ectoderm that rolls, forming the hollow tube, compared to other animal phyla, which have solid, ventral tubes. The dorsal nerve cord is later modified into the brain and spinal cord. Dorsal nerve cord is mainly found in phylum Vertebrata.
Dorsal means the "back" side, as opposed to the belly side (ventral).
The ventral nerve cord makes up the nervous system of some phyla of the invertebrates, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral ("belly", as opposed to back) plane of the organism. This characteristic is important in qualifying the difference compared to the chordates, which have a dorsal nerve cord.
1) The notochord is the defining structure of the phylum Chordata, which includes all vertebrates. In its "mature" state, the notochord is a rod of large cells constrained by a thick extracellular sheath and positioned between the developing spinal cord and gut. Turgor pressure generated by notochord cells exerted against the sheath gives the notochord stiffness, imparting the mechanical properties required for one of its main functions as the central axial skeletal element of the developing embryo.
2) The notochord exists transiently during the life of most vertebrates. During its short life, however, the notochord plays another critical role for developing embryos,.producing a variety of secreted growth factors, such as Sonic hedgehog, which instruct surrounding tissues to acquire particular differentiated fates. A number of embryological experiments, for example, tell us that, without notochord-derived signals, motorneurons in the spinal cord would not form, the pancreas insulin-producing cell would not differentiate, and the body muscles would not be produced properly. Without the axial skeletal support of the notochord, many lower vertebrate larvae, such as fish fry and tadpoles, become severely shortened and cannot swim or feed properly. Thus many of the mutations affecting zebrafish notochord development are named after the seven dwarves.