Nervous System Embryology and Congenital Malformations

Question 1

From what part of the embryo does the nervous system develop?

Answer 1

The embryonic ectoderm

Question 2

When does the CNS start to appear?

Answer 2

At the beginning of the third week

Question 3

How does the CNS initially form?

Answer 3

The ectoderm thickens to form the neural plate and the edges thicken and move upwards to form the neural folds

Question 4

How does the neural tube form?

Answer 4

The neural folds migrate towards each other and fuse at the midline

Question 5

When do the anterior and posterior neuropores close?

Answer 5

Anterior neuropore closes ~ day 25

Posterior neuropore closes ~ day 27

Question 6

What defects can be caused by failure of the neural tube to close properly?

Answer 6

Anencephaly
Encephalocoele
Spina bifida

Question 7

What causes anencephaly/exencephaly?

Answer 7

Failure of the anterior neuropore to close

Question 8

What is the result of anencephaly/exencephaly?

Answer 8

Skull fails to form
Brain tissue degenerates
Incompatible with life

Question 9

What is the cause of encephalocoele?

Answer 9

Herniation of cerebral tissue through a defect in the skull due to failure in closure of rostral neural tube
Most frequent in occipital region

Question 10

What is the cause of spina bifida?

Answer 10

Defective closure of the caudal neural tube

Question 11

What are the risk factors for spina bifida?

Answer 11

Genetic predisposition
Nutritional- too little folate, too much vitamin A
Environmental- hyperthermia

Question 12

When do the brain vesicles begin to develop?

Answer 12

With the closure of the anterior neuropore

Question 13

What are the names of the brain vesicles present in the fourth week?

Answer 13

Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

Question 14

What are the names of the brain vesicles present in the fifth week?

Answer 14

Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon

Question 15

What does the prosencephalon form?

Answer 15

Forms diencephalon and telencephalon which form:
Diencephalon:
-Thalamus
-Hypothalamus
-Pituitary gland
-Pineal gland
Telencephalon:
-Cerebral hemispheres
-Hippocampus
-Basal ganglia

Question 16

What do the mesencephalon form?

Answer 16

Superior and inferior colliculi

Question 17

What does the rhombenecephalon form?

Answer 17

Forms metencephalon and myelencephalon, which form:
Metencephalon:
-Cerebellum
-Pons
Myelencephalon:
-Medulla

Question 18

What does the caudal neural tube form?

Answer 18

The spinal cord

Question 19

What does the lumen of the neural tube form?

Answer 19

The ventricular system

Question 20

What do the neural crest cells form?

Answer 20

The peripheral nervous system neurons and glia

Question 21

What is lissencephaly?

Answer 21

Rare brain disorder caused by defective neuronal migration meaning that the gyri and sulci fail to develop
Results in severe mental impairment, failure to thrive and abnormal muscle tone
Many affected die before 10

Question 22

What is polymicrogyria?

Answer 22

Excessive number of small gyri

Variable degree of neurological problems

Question 23

What is microcephaly?

Answer 23

Small head and brain
Caused by genetics, drugs or infection (Zika virus)
Causes intellectual impairment, delayed motor functions, hyperactivity, seizures, balance problems etc

Question 24

What is porencephaly?

Answer 24

CSF filled cysts or cavities
Usually from postnatal stroke or infection
Causes delayed growth and development, seziures, hypotonia and intellectual impairment

Question 25

What is shizencephaly?

Answer 25

Large clefts of slits in brain
Caused by genetics, in utero stroke, infection
Causes paralysis, seizures, intellectual impairment and developmental delay

Question 26

What is diastematomyelia?

Answer 26

Spinal cord split longitudinally into two parts

Causes scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation

Question 27

What are the causes of intellectual impairment?

Answer 27

Genetics
Radiation
Infectious agents
Birth trauma
Postnatal insults
Maternal alcohol abuse