Neuro2 - CNS Embryology

Question 1

4 steps in the formation of the neural tube

Gastrulation
Neurulation
Neural Plate
Neural Tube

Answer 1

1.) Gastrulation - produces the notochord

2. ) Neurulation - induced by the notochord
   - produces the neural plate (area of neuroectoderm above the notochord)
3. ) Neural Plate - lateral edges elevates
   - the depressed mid region is the neural groove
4. ) Neural Tube - neural folds gradually approach each other in the midline and fuse
   - the neural tube is closed by day 28-32 (whole process takes place in 10 days)

Question 2

3 forms of neural tube defects

Diagnosis and Prevention

Answer 2

1. ) Cranial Defect - leads to anencephaly
   - abscence of cranial structures including the brain
   - incompatible with life

2.) Caudal Defect - leads to spina bifida

3. ) Elevation Defect - failure of the neural fold to elevate
   - leads to rachischisis which is incompatible w/ life
4. ) Diagnosis
   - raised maternal serum AFP tells you an open defect
   - used in combination with an ultrasound scan
5. ) Prevention - folic acid in the first trimester
   - mechanism of action is unknown

Question 3

4 features of spina bifida

Definition
Meningocele
Myelomeningocele
Hydrocephalus

Answer 3

1. ) Definition - incomplete closing of the spine and membranes around the spinal cord
   - most common in the lumbosacral region
2. ) Meningocele - less severe version
   - just the meninges and CSF occupying cyst
3. ) Myelomeningocele - more severe version
   - often associated with neurological defects
4. ) Hydrocephalus - accumulation of CSF in the brain
   - nearly always occurs with spina bifida
   - not managed –> increase in ICP –> cognitive delay

Question 4

Formation of the nervous system

Brain
Spinal Cord (+cauda equina)
Ventricular System (+abnormality)
Flexures
Neural Crest

Answer 4

1. ) Brain - cranially from the neural tube
   - 3 dilations –> 5 dilations (anatomical division)
2. ) Spinal Cord - tail of the neural tube (caudally)
   - at the 3rd month, spinal cord is same length as the verterbral column but then it stops growing
   - spinal roots must then elongate near the bottom which forms the cauda equina
3. ) Ventricular System - lumen of the neural tube
   - abnormality or any blockage –> hydrocephalus
   - treatment is a ventriculo-peritoneal (VP) shunt
4. ) Flexures - bending of the cranial NT to make space
   - cephalic flexure is in the midbrain region
   - cervical flexure is the spinal cord-hindbrain junction

5.) Neural Crest - migration of neural tube

Question 5

5 anatomical divisions of the brain and what they form

Telencephalon x1
Diencephalon  x5
Mesencephalon x1
Metencephalon x2
Myelencephalon  x1

Answer 5

1. ) Telencephalon - forebrain (prosencephalon)
   - forms the cerebral hemispheres, (aka the cerebrum)
2. ) Diencephalon - forebrain (prosencephalon)
   - forms the thalamus, hypothalamus and 3rd ventricle
   - also the epithalamus and ventral thalamus
3. ) Mesencephalon - midbrain (mesencephalon)
   - forms the midbrain
4. ) Metencephalon - hindbrain (rhombencephalon)
   - forms the pons and cerebellum
5. ) Myelencephalon - hindbrain (rhombencephalon)
   - forms the medulla

Question 6

4 features of neural crest cells

What are They?
Formation
Derivatives (nervous x4, H/N x3, other x3)
Defects

Answer 6

1. ) What are They? - temporary group of cells arising from ectoderm, giving rise to a diverse cell lineage
2. ) Formation - by the migration of cells from the neural tube during embryonic development
3. ) Derivatives - nervous system, H/N structures, other
   - ganglia, schwann cells, glial cells, leptomeninges
   - CT/bones of the head, C cells of thyroid, dermis
   - adrenal medulla, melanocytes, conotruncal septum
4. ) Defects - extremely vulnerable to environmental insult (esp. alcohol) but can also be genetic
   - example: DiGeorge syndrome