Describe how the notochord is formed
Prenotochordal cells migrate from primitive pit and form the midline and drive neurulation.
Neurulation initated by overlying ectoderm that differentiates to form neural plate - this tickens and its lateral edges rise up and the midline depresses to form a neurla groove. These edges then meet and fuse, forming a neural tube.
Describe the fusion of the neural tube. How can it lead to neural tube defects?
Neural tube fuses in a cephalic to caudal manner, producing anterior and posterior neuropores. These neuropores close on day 25 and 28 for anterior and posterior respectively. Any defects in closure can cause NTDs.
Describe how spina bifida occurs.
Failure of posterior neuropore to fuse.
What are the 2 main types of spina bifida? Briefly describe them.
Spina bifida occulta - Defect in vertebral arches resulting in lack of fusion of the vertebral arches
Spina bifida cystica - more severe. neural tissue and/or meninges protrude through skin to form a cyst. If only fluid filled meninges in sac = meningocele. If neural tissue also in sac = meningomyelocele
What is anencephaly and how does it occur?
Failure of anterior neuropore to close resultingin absence of brain. Incompatible with life
What is rachischisis?
Posterior neuropore fails to close resulting in vertebrae of spine being unfully formed, leaving the spinal cord exposed
How can neural tube defects be detected before birth?
Raised serum alpha-fetoprotein in mother or on USS
Why does the spinal cord roots have to stretch to exit the correct spinal level?
Up to 3 months During development the spinal cord is the same length of the vertebral column, and exits the column at the same level. However, after this point the vertebral column grows faster and so the spinal roots must elongate to exit their original IV foramina
What are the derivatives of the telencephalon and the diencephalon?
Telencephalon - cerebral hemisphere
diencephalon - thalamus
What are the derivatives of the mesencephalon?
What are the derivatives of the metencephalon?
pons and cerebellum
What are the derivatives of the myelencephalon?
Why does the brain have so many folds? Where do the 2 flexures of the spinal cord occur?
The cranial end of the neural tube rapidly enlarges and exceeds the available space, and therefore begins to fold up.
Cephalic flexure occurs at midbrain region. Caudal flexure occurs at spinal cord hindbrain junction
What is the ventricular system in the adult brain? From what does it develop?
Acts as a reservoir of CSF within the brain, cushioning the brain and spinal cord.
Develops from the neural tube lumen.
Label the ventricles of the nervous system
What cells produce CSF in the ventricular system?
cells of ventricular lining
What happens to the neural crest cells at the lateral border of the neuroectoderm tube? Why are these cells vulnerable?
Become displaced and enter mesoderm and transition to mesenchymal cells. They input into a number of different structures such as adrenal medulla, schwann cells, or c cells of thyroid.
Vulnerable to environmental insults esp. alcohol
What is hirschprungs disease?
Disorder of the gut which is due to failure of neural crest cells to migrate completely. Affected part of colon fails to relax causing obstruction.