Physiological and Pathological formation of the brain and spinal cord

Question 1

Spinal cord development

Answer 1

• 3rd week – gastrulation (endoderm, mesoderm, ectoderm)
• 4th week - Ectoderm thickens in midline to form the neural plate
• Ectoderm undergoes differential mitosis to cause the formation of a mid-line groove (neural groove)
• This groove deepens and eventually detaches from the overlying ectoderm to form the neural tube

Question 2

neural crest cells

Answer 2

• Lateral to the neural grove the presumptive neural crest cells form – help to develop other cells such as Schwann cells and neurones in the ectoderm and adipocytes and osteoblasts in the mesoderm
They also form:
o the sensory dorsal root ganglia of spinal cord V/VII/IX/X
o Adrenal medulla
o Bony skull
o Meninges

Question 3

abnormalities of the spinal cord

Answer 3

The neural tube usually closes at the end of 4th embryonic week
o Failure to close cephalic region – anencephaly
o Failure to close spinal region – spina bifida
Collectively called – neural tube defects

Question 4

causes of spina bifida

Answer 4

faulty induction, environmental teratogens acting on neurepithelial cells

Multifactorial: genetics, folic acid, maternal diabetes

Question 5

syndromic causes of neural tube defects

Answer 5

have a higher recurrence risk: e.g. Meckel syndrome: extra fingers, cystic kidney malformation, NTD – ¼ chance of a sibling being affected

Question 6

development of the brain

Answer 6

• Rostral portion of neural tube develops into brain – grows faster than caudal end which develops into spinal cord and ventricles of brain
5th week – 3 primary brain vessels
1. Prosencephalon (forebrain)
2. Mesencephalon (midbrain)
3. Rhombencephalon (hindbrain)
7th week – differentiation into secondary brain vesicles
1. Prosencephalon → Telencephalon & diencephalon
2. Mesencephalon → mesencephalon
3. Rhombencephalon → Metencephalon & myelencephalon

Question 7

brain development defects

Answer 7

Microcephaly – reduced head circumference – insuffient production of neurones
Macrocephaly – increased head circumference

Question 8

Hydrocephalus

Answer 8

o Abnormal accumulation of CSF with increased intercranial pressure
o Can cause macrocephaly in children (therefore always scan increasing head size)
o Often due to blocked cerebral aqueduct
o Obstructive (non-communicating): e.g. tumour, haemorrhage
o Non-obstructive (communicating) e.g. increased CSF production

Question 9

Anencephalous

Answer 9

• Cephalic neural tube fails to close
• Skull vault absent
• Death
• 4x more common in females