Neurulation & Somitogenesis Flashcards
What is neurulation?
Neurulation is the formation of the vertebrate nervous system in embryos.
When does the neural plate form?
Day 19
How is the notochord developed?
Some mesodermal cells migrate cranially in the midline of the mesodermal layer which forms the rod like notochord.
What happens as a result of the notochord forming?
The notochord induces the formation of the thick and flat neural plate in the ectoderm. This is the Neuroectoderm.
How is the neural tube formed?
The neural plate folds in on itself to form the neural tube.
What does the neural tube differentiate into?
The spinal cord and brain
What do neural crest cells derive into?
Migrate out to form PNS
Describe the process of neural tube formation. (4)
- Neuroectodermal tissues differentiate to form neural plate.
- The neural plate bends dorsally and converges at the neural crest.
- The closure of the neural tube disconnects the neural tube from the ectoderm. Neural crest cells differentiate to form PNS
- Other mesoderm cells differentiate into somites.
What are somites
Paraxial mesoderm differentiates and divides into the precursors of the axial skeleton and skeletal muscle
What happens to the notochord?
It degenerates and only persists as the nucleus pulposus of the intervertebral discs.
How many pairs of somites are there at the end of week 5?
42-44 pairs
What can somites differentiate into?
Cartilage then bone of the axial skeleton. Muscles o the rib cage, limbs and back. Connective tissue of the dermis.
What are the 3 types of somites?
Sclerotome (Bone), Myotome (Muscle), and Dermatome (Connective tissue)
Draw sclerotome, myotome and dermatome
in notes
What can neural crest cells differentiate into?
- Spinal Ganglia
- Ganglia of the autonomic nervous system
- Ganglia of some cranial nerves
- Sheaths of peripheral nerves
- Meninges of brain and spinal cord
- Melanocytes
- Suprarenal medulla
- Skeletal and muscular components of the head
At what days do the anterior and posterior neuropores close?
Anterior - Day 24
Posterior - Day 26
What does the forebrain develop into?
The Prosencephalon develops into the cerebrum and diencephalon
What does the midbrain develop into?
The mesencephalon develops into the brain stem
What does the hindbrain develop into?
The Rhombencephalon develops into the Brainstem, Cerebellum and spinal cord
What are some causes of teratogenesis and at what stage of pregnancy does this occur?
Can happen throughout but most prevalent at week 5, Alcohol, amphetamines, hyperthermia, x rays etc etc
What is the cause of Spina Bifida
Failure of fusion of vertebral arches
What are the common tell tale signs of the different types of spina bifida?
Spina Bifida Occulta - Hair growth on lower spine
Spina Bifida Meningocele - A small bulge on lower spine
Spina Bifida. The protrusion of meninges.
Myelomeningocele - A large bulge from lower spine
What is encephaloceles?
Like spina bifida but in the back of the head
What is anencephaly?
A failure of the neural tube to close, only have frontal lobe of brain.
What is hydrocephalus?
Build up of fluid on the brain, as a result of neurulation not occurring properly
