Physiological and pathological formation of the brain and spinal cord

Question 1

What happens in week 3 of embryo?

Answer 1

Gastrulation

Ectoderm - skin, nervous system

Endoderm - epithelial lining of gut and respiratory system, liver and pancreas

Mesoderm - notochord, muscular system

Question 2

Ectoderm thickens in midline to form what?

Answer 2

neural plate

Question 3

What do signals from notochord cause

Answer 3

Inward folding of ectoderm at the neural plate

Question 4

What fuses and disconnects to form an autonomous neural tube?

Answer 4

ends of the neural plates

Question 5

Where does the presumptive neural crest cells lie?

Answer 5

Lateral to the neural groove

Question 6

What types of cells do the ectoderm turn into?

Answer 6

Melanocytes, Schwann cells and neurons

Question 7

What types of cells do the mesoderm cells turn into?

Answer 7

Osteoblasts, adipocytes and chondrocytes

Question 8

What do neural crest cells make?

Answer 8

Sensory dorsal root ganglia of spinal cord and V/ VII / IX / X

Schwann cells

Adrenal medulla

Bony skull

Meninges

Question 9

When does the neural tube usually close?

Answer 9

End of 4th week

Question 10

What causes anencephaly?

Answer 10

Failure to close cephalic region

Question 11

What causes spina bifida?

Answer 11

Failure to close spinal region

Environmental factors may contribute - lack of folic acid, maternal diabetes.

Question 12

What is meningocele?

Answer 12

Protrusion of the meninges, may or may not be skin covering it.

Question 13

What is Myelomeningocele?

Answer 13

Protrusion and opened spinal cord

Question 14

When are these neural tube defects normally known due to antenatal scanning?

Answer 14

By 13-14 weeks gestration

Question 15

What could cause weakness of lower limbs?

Answer 15

L2-L4 lesion of spinal cord

Probably a mixed upper and lower motor defect

Question 16

Brain at 4 weeks

Answer 16

Prosencephalon - gives rise to cerebral hemispheres and thalamic structures

Mesencephalon - midbrain

Rhombencephalon - medulla, pons and cerebellum

Question 17

Brain at 6 weeks

Answer 17

Regions divides into more regions. Positions change.

Rhombencephalon will give rise to 4th ventricle, medulla, pons and cerebellum

Question 18

What is hypoplasia?

Answer 18

Underdevelopment of parts of brain

Question 19

How many layers are there in the cerebral cortex?

Answer 19

6

Proliferation of stem cells and migration to right positions. Controlled by many different genes.
When this doesn’t go as it should, results in intellectual disabilities.

Stem cells produce neurons. Neurogenesis.

Question 20

What is microcephaly and macrocephaly mean?

Answer 20

Top/bottom 2.5% size of head circumference.

Microcephaly - reduced head size.
Could be caused by: Down’s Syndrome, toxic exposures during pregnancy

Macrocephaly - increased head size

Question 21

What is periventricular nodular heterotopia?

Answer 21

Abnormal migration of neurons.

On MRI shows as nodules.

Can result in seizures, learning issues, weak arm.

Question 22

Cerebrospinal fluid

Answer 22

Cushions brain and helps circulate metabolites

Around 120 mls

Filtrate of blood, produced as filtrate of blood at choroid plexuses in ventricles.

Absorbed via arachnoid granulations in superior sagittal sinus.

Question 23

What happens if block in intraventricular canal?

Answer 23

In child, head expands as fissures not cemented. Macrocephaly. So always scan child with increasing head size.

In adult, brain = squished –> die.

Question 24

What is hydrocephalus?

Answer 24

Accumulation of CSF with increased intracranial pressure