Nervous system embryology and malformations

Question 1

Does the nervous system develop from ectoderm, mesoderm or endoderm?

Answer 1

ectoderm

Question 2

What week does the CNS appear?

Answer 2

3

Question 3

What is the neural plate?

Answer 3

Thickening of ectoderm anterior to the primitive node

Question 4

What are neural folds?

Answer 4

Edges of the neural plate thicken and move upwards to form these

Question 5

How is the neural tube formed?

Answer 5

Neural folds migrating towards eachother and fusing in the midline

Question 6

Is the neural tube initially open or closed?

Answer 6

open

Question 7

When does the anterior and posterior neuropore close?

Answer 7

anterior = day 25 
posterior = day 27

Question 8

What can failure of the neural tube closing lead to? Give 3 examples

Answer 8

death

NTD = spina bifida, anencephay, encephalocoele

Question 9

Which neural tube defect is incompatible with life?

Answer 9

anencephaly

Question 10

Is anencephaly more common in males or females?

Answer 10

females by 4 times

Question 11

What happens in anencephaly?

Answer 11

anterior neuropore fails to close and the skull fails to form leading to brain tissue degeneration

Question 12

Craniorachischisis

Answer 12

Entire neural tube fails to close

Question 13

What is encephalocoele and what causes it?

Answer 13

Herniation of cerebral tissue through a defect in the skull due to failure of rostral tube closure

Question 14

Where is encephalocoele most common?

Answer 14

occipital region

Question 15

What causes spina bifida?

Answer 15

Defective closure of the caudal neural tube

Question 16

What is affected in spina bifida?

Answer 16

tissue overlying spinal cord

Question 17

What is spina bifida?

Answer 17

non-fusion of vertebral arches

Question 18

Spina bifida occulta - what causes it?

Answer 18

failure of embryonic halves of vertebral arches to grow normally and fuse

Question 19

What vertebral level does spina bifida occulta occur and what is a sign?

Answer 19

L5/6

dimple with patch of hair

Question 20

What is spina bifida cystica?

Answer 20

Protrusion of spinal cord and/or meninges through vertebral arch defect

Question 21

Spina bifida with meningocele - what is protruding??

Answer 21

CSF and meninges

Question 22

spina bifida with meningiomyelocle - what else is included in the protrusion?

Answer 22

nerve roots/spinal cord - neurological defecit

Question 23

What is spina bifida with meningiomyelocle associated with?

Answer 23

hydrocephalus

Question 24

What is myeloschisis?

Answer 24

Rare form and most severe of spina bifida

spinal cord open in affected area as neural tube fails to close

Question 25

4 prevention methods of spina bifida/NTD

Answer 25

folic acid supplements ultrasound amniocentesis blood test

Question 26

What are you looking for in the blood in prenatal diagnosis of NTDs and why?

Answer 26

AFP - alphafetoprotein | from foetus liver which means an open communication

Question 27

Risk factors for NTDs

Answer 27

genetic predisposition Nutrition - too much vitamin A, too little folate Environmental eg sodium valproate, hyperthermia

Question 28

Name the 3 primary brain vesicles

Answer 28

Prosencephalon mesencephalon rhombencephalon

Question 29

Name the 5 secondary brain vesicles

Answer 29

``` Telencephalon diencephalon mesencephalon metencephalon myencephalon ```

Question 30

When does the cephalic flexure form and where is it?

Answer 30

end of 3rd week | between midbrain and hindbrain

Question 31

When does the cervical flexure form and where is it?

Answer 31

End of 4th week | between hindbrain and spinal cord

Question 32

When does the pontine flexure form and where is it?

Answer 32

5th week | in hindbrain

Question 33

Name the 3 flexures of the vesicles

Answer 33

cephalic cervical pontine

Question 34

What does the telencephalon form?

Answer 34

cerebral hemispheres hippocampus basal ganglia

Question 35

What does the diencephalon form?

Answer 35

thalamus hypothalamus pituitary gland pineal

Question 36

What does the mesencephalon form?

Answer 36

superior and inferior colliculi | midbrain

Question 37

What does the metencephalon form?

Answer 37

cerebellum | pons

Question 38

What does the myencephalon form?

Answer 38

medulla

Question 39

What does the caudal neural tube form?

Answer 39

spinal cord

Question 40

What does the lumen of the neural tube form?

Answer 40

ventricular system

Question 41

When does CSF begin to form?

Answer 41

week 5

Question 42

What is hydrocephalus and what is the main cause?

Answer 42

Accumulation of CSF resulting in enlarged brain and cranium | usually due to blocked aqueduct so lateral and 3rd ventricle cannot drain into 4th ventricle to be absorbed

Question 43

Causes of hydrocephalus

Answer 43

genetics prenatal viral infection intraventricular haemorrhage spina bifida cystica

Question 44

The neural tube is initially a single layer of.....cells

Answer 44

neuroepithelial

Question 45

What do the neuroepithelial cells go on to form?

Answer 45

Neurons, astrocytes, oligodendrocytes, ependymal cells - CNS

Question 46

What is microglia formed by?

Answer 46

mesenchymal cells - mesodermal in origin

Question 47

What do neural crest cells go on to form?

Answer 47

cells of PNS, autonomic NS and non neuronal cells eg melanocytes, adrenal medulla, meninges, facial bones and cartilage

Question 48

How does the spinal cord position change?

Answer 48

initially entire length of vertebral column but then dura and vertebral column grow more rapidly

Question 49

What is lissencephaly?

Answer 49

smooth brain - no sulci or gyri

Question 50

What do people with lissencephaly normally die of?

Answer 50

problems with swallowing and aspiration

Question 51

Polymicrogyria - what is it and what are the symptoms?

Answer 51

excessive number of small gyri | variable - mental retardation, seizures, motor defecits

Question 52

What is microcephaly and give a recent common cause of this

Answer 52

small brain | Zika virus

Question 53

What is porencephaly and what does it usually follow?

Answer 53

CSF filled cysts or cavities | postnatal stroke or infection

Question 54

What is schizencephaly?

Answer 54

Large slits or clefts

Question 55

What is diastematomyelia and what are the symptoms/signs?

Answer 55

split cord longitudinally | vertebral anomalies, scoliosis, hairy patch, loss of sensation

Question 56

Causes of intellectual impairment

Answer 56

Formation of brain cells affected due to maternal alcohol, genetic, radiation, infection, birth trauma, postnatal insults eg meningitis