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
imaging showing early development of the three primary brain vesicles
Forebrain vesicles- day 26
- We can start to see laterally directed outgrowths of the diencephalon
- These outgrowths (grey) will become the optic nerves
- Growing towards the developing eyes to connect up with them
label this embryo at day 35-38
Focussing in on the nervous system at 35-38 days
development of the forebrain (prosencephalon) vesicle at 35-38 days
- Divided into two subdivision:
- Cranially- telencephalon (cerebral hemispheres)
- Dark green
- Caudally- Diencephalon (thalamus, hypothalamus and optic nerve)
- Light green
- Cranially- telencephalon (cerebral hemispheres)
development of the midbrain (mesencephalon) vesicle at 35-38 days
- Only has 1 division
summary of vesicle organisation
diencephalon
thalamus, hypothalamus and optic nerve
etencephalon
pons and cerebellum
- Myelencephalon
medulla
Day 45- Further elabortion of the neural tube esp at cranial end
-
Telencephalic outgrowth forming cerebral hemisphere
- Will develop frontal, parietal, temporal, occipital and limbic lobes (5 lobes of the brain)
- Diencephalon
Day 60
-
We can start to see:
- Cerebellum
- Cerebral hemispheres
- Spinal cord and dorsal root ganglia
- Peripheral nerves are growing into the upper and lower limbs
cranial nerves
Ventricular system development (at day 60)
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- Neural canal dilates within the cerebral hemisphere- corresponding to the lumen of the neural tube (like a mould)- forming the lateral ventircles
- Chororid capillary plexus which invaginates the roof plates of the ventricles secretes CSF which flows through ventricular system
- These communicate with the third ventricle contained within the diencephalon via the interventiruclar foramen (foramen of monro)
- 3rd and 4th ventricles communicate through the cerebral aqueduct (aqueduct of sylvius) in the midbrain
- CSF exits 4th ventricle through 3 apertures in its roof known as foramen magendie (in midline) and the right and left foramen luschka)
why does the ventricular system look proprotionally larger in developing embryos than in humans
- Much larger than in the adult ventricular system due to neurones not having proliferated yet
- Shape corresponds to the cerebral hemispheres
- Quite large cavity in brain at this point since we haven’t had much growth of the neural tissue yet
