Somitogenesis and neural tube formation Flashcards
In which stage of foetal development does neurulation occur?
Organogenesis
What is neurulation?
Process of neural tube formation that occurs during organogenesis
What structure is formed in gastrulation that induces formation of the neural tube?
Notochord
What is the first inductive effect of the notochord?
Causes ectodermal cells to differentiate into neuroectoderm
What is the structure of neuroectoderm?
Pseudostratified columnar neuroepithelium
Where does the open neural plate begin to form during neurulation?
Cranial end of embryo
What direction does the open neural plate differentiate in during neurulation?
Cranial-caudal direction
What is the 2nd inductive effect of the notochord, that occurs once the open neural tube has been completed?
Induces folding of lateral surface ectoderm and neuroectoderm to form neural folds
When neural folds form in the open neural tube, what is the depression in the middle called?
Neural groove
How is the open neural tube closed up to form a hollow neural tube?
Neural folds on each side of the neural groove fuse together
Where are neural crest cells formed?
Neural plate lateral regions
When do neural crest cells detach from the neural tube?
During neural tube formation
What happens to neural crest cells after they detach from the forming neural tube?
Migrate in embryo to contribute to tissues/organs
When does paraxial mesoderm develop during neurulation?
During neural tube formation
What is meant by paraxial mesoderm being organised into bilateral columns?
There are 2 streaks (columns) of paraxial mesoderm in total, each streak is lateral on each side of the neural tube
What intermediate and definitive structure is formed from paraxial mesoderm?
Intermediate structure is somitomere
Definitive structure is somite
During somitogenesis, what do the bilateral columns ultimately divide into?
Paired somites, so that one somite is on each side of the neural tube
How are somitomeres formed from paraxial mesoderm?
Paraxial mesodermal cells come together to form blocks called somitomeres, so there is incomplete segmentation between the blocks
How are somites formed from somitomeres?
Somitomeres become compacted and bound by epithelium to form somites, which are completely segmented blocks of paraxial mesoderm
What direction does somitogenesis occur in?
Craniocaudal sequence
What 2 neural tube formation events are occurring at the same time of somitogenesis?
Formation of neural folds, regression of primitve streak
How many somite pairs are formed in total?
38
Which somitomeres don’t condense into somites?
Somites in more cranial parts of head
Where do the first pairs of somites develop?
Occipital region (back of head)
What are the 2 subdivisions of a somite?
Mesenchymal sclerotome, dermomyotome
What cells in the somite differentiate into mesenchymal sclerotomes?
Ventromedial
What cells in the somite differentiate into dermomyotomes?
Dorsolateral
Which surface of the embryo do somites develop along?
Dorsolateral
What 3 type of muscles do myotomes develop into?
Limb muscles in developing limbs
Hypaxial (ventrolateral)
Epaxial (dorsal)
What do dermatomes develop into?
Skin dermis
Give 2 structures that mesenchymal sclerotomes develop into?
Vertebral column (spine), ribs
What is the definition of the notochord, and why does it need to develop before the neural tube?
Temporary structure in embryo midline that acts as axis around which vertebral column develops
Neural tube forms along notochord
