Development is the process by which an organism develops from a zygote to its full 3D structure. This journey starts from a single cell to a complex multicellular organism, which does not end at birth. It continues with childhood, puberty and through to early adulthood. All embryos have the same conserved embryonic developmental plan (CEDP), due to which all embryos look the same. Some key mechanisms involved in these developmental phases are growth, differentiation, morphogenesis, gastrulation, and neurulation.
In development, signaling of a vast array of different proteins, by different groups of cells, allow cells to gain information about migration, proliferation, differentiation or something else. Organisation of these cells determine their roles and positions, so whether they form the cranial (head) or caudal (tail) end. Morphogenesis is the formation of shape and movement and manipulation of these cells to assemble tissues and organs. Progressively, cells are guided through migration by attractive and repulsive cues; similar cues also help define tissue boundaries. Therefore, exposing cells to different concentrations of morphogen can change their outcome e.g. cell type; digit formation- a simple structure has become more complex (Webster and de Wreede, 2016).
The Contribution of Gastrulation and Neurulation to the Embryo Formation
Gastrulation is the formation of the germ layers Ectoderm, Mesoderm, and Endoderm. During this process, the cell reorganises to change from a simple blastula to a multi-layered organism, with the cells moving to a more interior location of the cell. Neurulation is the transformation of the neural plate into the neural tube (Larsen, Sherman and Potter, 2001). Both these processes work collaboratively to aid the initial formation of the nervous system. The progenitor cells of the neural tube are known as neural precursor cells. These precursors are dividing stem cells that produce more precursors and, eventually (Quizlet.com, 2018), non-dividing neuroblasts that differentiate into neurons (Purves et al., 2001).
As a result of their proximity to the notochord, the cells at the ventral midline of the neural tube differentiate into a special strip of epithelial-like cells called the floor plate (Purves et al., 2001). The close proximity allows more signals to be sent, more efficiently. Once the nervous system and brain have been developed, they can speed up the overall developmental process.
The forebrain grows to contain the thalamus, hypothalamus, pituitary gland and pineal gland. The thalamus is responsible for the sensory relay in the brain.
The hypothalamus controls motivated behavior by regulating the release of hormones from the pituitary gland. It is responsible for fight, flight, feeding and sex. The pituitary gland will become an endocrine gland, which produces critical hormones that control various bodily functions. The Pineal gland controls melatonin, a hormone that affects the modulation of wake/sleep patterns and seasonal functions. The midbrain becomes a portion of the central nervous system associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation. The hindbrain is a developmental categorisation of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together, they support vital bodily processes (Brain atlas – Hindbrain, n.d.).
Alongside, the notochord is a longitudinal structural element of chordates and of the early embryo of vertebrates, in both of which it plays an organisational role in nervous system development (ScienceAid Editor) & XanthousOfTheThirdQuadrant,Moreau, n.d.). In later vertebrate development, it becomes part of the vertebral column. It is also the defining structure of the chordates, and has essential roles in vertebrate development. It serves as a source of midline signals that pattern surrounding tissues and as a major skeletal element of the developing embryo (Stemple, 2005). Next somites subdivide into the sclerotomes, myotomes, and dermatomes that give rise to the vertebrae of the vertebral column, rib cage, and part of the optic cup and lens vesicle. On or about day 22, two small grooves develop on each side of the developing forebrain in the neural folds.