Lecture 2- Development of the nervous system 1/2 Flashcards
Day 18- Primitive disc
- At day 18 primitive node and streak form in the epiblast cells (will become trilaminar disc)
- Epiblast from superior view= future ectoderm (skin and NS)
what occurs along the primitive streak
- process of invagination will occur–> gastrulation
Gastrulation
- formation of trilaminar embryo
- Epiblast cells approach primitive streak and invaginate
- Go onto form the other 2 embryonic layers
- Mesoderm
- Ectoderm
how is the notochord formed
- Part of the mesoderm will grow cranially from the primitive pit –> forming notochord
role of notochord
- inducts the overlying ectoderm to form the neural tube and the rest of the CNS
In adult CNS the ……………. ………………….is the only remnant of the notochord
nucleus pulposus
Day 20- development of ectoderm to create CNS
- Skin ectoderm (pink)
- Neuroectoderm (green)
- Will form neural tube
- Cranial end is bigger and more sophisticated than caudal end will become brain
outline how the neural tube is created
- Under direction of the notochord, the ectoderm is rising up, folding and then invaginating down forming the neural tube
Ectoderm will start to elevate (green sides) to form neural folds and groove
why does the neural tube run along the axis of the foetus
Notochord runs cranially to caudally (grey line) invagination along the axis of the foetus
Day 22- Neurulation
- Where the skin ectoderm crosses the green neuroectoderm = where neural tube has fully invaginated (in the cervical region)
- If we look at a cross section at this level= formation of a complete tube (neural tube)
- Skin ectoderm has healed up over this point forming a body wall
- From this cervical point, the neural tube will ‘zip up’ along its length
- Cranially to form the brain
- Caudally to form the spinal cord
neurulation- a stage where things can go wrong
- If the neural tube fails to ‘zip up’ in the cranial direction –> anencephaly
- If cranial tube doesn’t close- brain wont form
- Incompatible with life
- If the neural tube fails to ‘zip up’ in the caudal direction–> spina bifida
- Failure of closure of neural tube in caudal direction
neural crest cells
At the apices of the neural folds we have a further population of cells called the neural crest cells
- Once the neural tube has closed these neural crest cells become free and, migrate to many places in the embryo
- Diverse tissue sets
- Head and neck
- Heart
- Melanocytes in skin
- Sensory and autonomic ganglia
once complete invagination of the cranial and caudal ends has occured what can be seen
somites
- We can see somites which will form future, skin, muscles and vertebrae
Day 26- Formation of 3 brain vesicles
- Very simple at this stage and bears little resemblance to adult CNS
- Except we can see cranial end has developed three swellings (vesicles) and flexures
- Forebrain
- Midbrain
- Hindbrain
- Flexures: midbrain (cephalic) flexure and cervocal fleuixre (junction between brainstem and cervical spinal cord
- Except we can see cranial end has developed three swellings (vesicles) and flexures