Development of the nervous system

Question 1

Neurulation

Answer 1

After gastrulation
Formation/closure of neural tube
During 3rd week of intrauterine life
Induction of surface ectoderm by underlying notochord
Midline cells in region cranial to primitive node begin to proliferate
Formation of thickened epithelium, which eventually folds

Question 2

Closure of neural tube

Answer 2

Closure begins in cervical region then proceeds upwards (cranial) and downwards (caudal) in zip-like fashion
current evidence: multiple closure sites
Last regions:
- anterior neuropore (25th day post-fertilization)
- posterior neuropore (27th day post-fertilization)
Neural canala: central canal of spinal cord and ventricles of the brain

Question 3

Layers of neural cells

Answer 3

Neuroepithelial cells –> neuroblasts –> neurons
Pseudostratified epithelium
Neuroepithelial cells also form neural glia –> astrocytes, oligodendrocytes
Ventricular layer: little nuclei, next to lumen, become ependyma
Intermediate (mantle) layer: thickest, become gray matter of spinal cord and neurons, lots of nuclei
Marginal layer: axons of nerve cells, white matter of spinal cord

Question 4

Neural crest cells

Answer 4

Formed at crest of neural folds
Ectodermal in origin
Change appearance from ectodermal (flat) to mesenchymal (spindle-shaped)
- detach from ectoderm and migrate extensively
Pluripotent
Function severely damaged by maternal alcohol abuse

Question 5

FASD

Answer 5

most common avoidable mental retardation
low birth weight
delayed psychomotor skills
facial abnormalities: small eyes, decreased nasal bridge, very thin upper lip
Delayed psychological manifestations

Question 6

Types of spina bifida

Answer 6

Occulta (unfused vertebral arch, tuft of hair above)
Meningocele (Large CSF-filled subarachnoid space)
Meningomyelocele (Spinal cord displaced outside)
Myeloschisis (open spinal cord)

Question 7

Spina bifida etiology

Answer 7

multifactorial
Hyperthemia
Valproic acid
excessive intake of vitamin A

Question 8

Spina bifida Dx

Answer 8

Ultrasound (8-10 weeks)

AFP in maternal serum and amniotic fluid

Question 9

Spina bifida prevention

Answer 9

0.4 mg folic acid daily before and during pregnancy

Question 10

Development of the brain

Answer 10

Closure of anterior neuropore –> 3 dilatations at the cranial end of neural tube
- primary brain vesicles: forebrain, midbrain, hindbrain
Vesicles further divide (except for midbrain) to produce five secondary brain vesicles

Question 11

Telencephalon

Answer 11

cerebral hemisphereslateral ventricle

Question 12

Diencephalon

Answer 12

hypothalamus, part of pituitary

3rd ventricle

Question 13

Mesencephalon

Answer 13

Midbrain
cerebral peduncles
superior and inferior colliculi
cerebral aqueduct

Question 14

Metencephalon

Answer 14

pons and cerebellum

4th ventricle

Question 15

Myelencephalon

Answer 15

Medulla oblongata

4th ventricle

Question 16

Flexures of the brain

Answer 16

grows rapidly, bends ventrally –> flexure formation
Result in analteration to basic arrangement of gray and white matter
Flexure in pontine region –> thinning of dorsal wall (roof) of
Cervical, midbrain (cephalic) and pontine flexures