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Development of the neural tube

Q: When does neural tube formation start and where?

Starts around day 22 at the level of 4 occipital somites .

Q: When are the neuropores of the neural tube fully closed?

Cranial neuropore: closed by day 24 Caudal neuropore: closed by day 26

Q: What happens to the neural plate during tube closure?

The neural plate continues expanding while folding inward to form the neural canal .

Q: When do neural crest cells (NCCs) form?

Neural crest cells (NCCs) are induced to form between the ectoderm and neurectoderm during gastrulation.

Q: Where do neural crest cells (NCCs) migrate to once neurulation (folding of neural plate into neural tube) starts?

During neurulation , neural crest cells (NCCs) detach from the lateral margin of neural folds before closure of neuropores to migrate from caudal end of prosencephalon to caudal end of spinal neural tube.

Q: What are the three populations of neural crest cells (NCCs) and what do each population of NCCs give rise to?

1. Cranial neural crest - structures of face and head, peripheral nervous system 2. Cranial and trunk neural crest - formation of structures in both face and head & nervous system 3. Trunk neural crest - sensory and sympathetic neurons, glia of peripheral nervous system

Q: What causes neural tube defects?

Failure of neural tube closure during neurulation, leading to exposure or malformation of neural tissue.

Q: What is total dysraphism or craniorachischisis?

Complete failure of neural tube closure — the entire neural tube remains open and fused to the surface (ectoderm)

Q: What is localized dysraphism?

Partial failure of closure of neural tube —only part of the neural tube remains open or fused to the surface (ectoderm)

Q: What is myeloschisis/spina bifida aperta?

A type of dysraphism where lumbosacral (lower back) region of the neural tube didn’t close, leading to development of an open spinal cord.

29 important questions on Development of the neural tube

When does neural tube formation start and where?

Starts around day 22 at the level of 4 occipital somites.

How does neural tube closure directionally proceed?

It occurs bidirectionally

When are the neuropores of the neural tube fully closed?

Cranial neuropore: closed by day 24

Caudal neuropore: closed by day 26

What happens to the neural plate during tube closure?

The neural plate continues expanding while folding inward to form the neural canal.

When do neural crest cells (NCCs) form?

Neural crest cells (NCCs) are induced to form between the ectoderm and neurectoderm during gastrulation.

Where do neural crest cells (NCCs) migrate to once neurulation (folding of neural plate into neural tube) starts?

During neurulation, neural crest cells (NCCs) detach from the lateral margin of neural folds before closure of neuropores to migrate from caudal end of prosencephalon to caudal end of spinal neural tube.

What are the three populations of neural crest cells (NCCs) and what do each population of NCCs give rise to?

1. Cranial neural crest - structures of face and head, peripheral nervous system
2. Cranial and trunk neural crest - formation of structures in both face and head & nervous system
3. Trunk neural crest - sensory and sympathetic neurons, glia of peripheral nervous system

What causes neural tube defects?

Failure of neural tube closure during neurulation, leading to exposure or malformation of neural tissue.

What is total dysraphism or craniorachischisis?

Complete failure of neural tube closure — the entire neural tube remains open and fused to the surface (ectoderm)

What is localized dysraphism?

Partial failure of closure of neural tube—only part of the neural tube remains open or fused to the surface (ectoderm)

What is myeloschisis/spina bifida aperta?

A type of dysraphism where lumbosacral (lower back) region of the neural tube didn’t close, leading to development of an open spinal cord.

What is meroencephaly/acrania?

A type of dysraphism where the cranial (head) region of the neural tube didn't close, causing malformation or exposure of the brain.

What is spina bifida occulta?

A mild neural tube defect that is usually caused by a single vertebral arch failing to fuse. It is characterised by tuft of hair, pigmented nevus, angioma/lipoma marks on surface of defect.

What is spina bifida cystica?

A severe form of spina bifida where the neural tube fails to close properly, causing fluid-filled sacs (celes) to form on the back.

What are the two subtypes of spina bifida cystica?

1. Meningocele - only the dura and arachnoid protrude, while the spinal cord stays in place.
2. Meningomyelocele - both the dura & arachnoid and the spinal cord protrude

What are the primary brain vesicles formed from the early neural tube?

1. Prosencephalon (forebrain)

2. Mesencephalon (midbrain)

3. Rhombencephalon (hindbrain)

Primary brain vesicles are first major divisions of a developing brain.

What is the mesencephalic flexure and why does it form?

The mesencephalic flexure is a 90° bend in the midbrain (mesencephalon) region of the neural tube. It forms because the forebrain (prosencephalon) grows faster than the midbrain, forcing the neural tube to bend ventrally.

What are the four structures that the neural tube gives rise to in week 4?

1. Prosencephalon
2. Mesencephalon
3. Rhombencephalon
4. Spinal cord

What are the two structures derived from prosencephalon in week 5, and which parts of the brain does it give rise to in week 6?

1. Telencephalon —> paleocortex, corpus striatum, neocortex
2. Diencephalon —> epithalamus, thalamus, infundibulum, hypothalamus

What does mesencephalon differentiate into in week 5 and week 6?

In week 5, mesencephalon doesn't differentiates. In week 6, mesencephalon gives rise to tectum, tegmentum, and cerebral peduncles.

What are the two stuctures derived from rhombencephalon in week 5, and which parts of the brain does it give rise to in week 6?

1. Metencephalon —> cerebellum, pons
2. Myelencephalon —> medulla

How does the spinal cord differentiate from week 4 to week 6?

The spinal cord maintains its state of a spinal cord.

What are the two main categories of CNS developmental malformations?

1. Cerebellar malformations
2. Cerebral cortical malformations

What are the three types of cerebellar malformations?

1. Hypoplasia

2. Dysplasia

3. Heterotopia

What are the possible causes of cerebellar malformations?

Both genetic and environmental causes

What are the three types of cerebral cortical malformations?

1. Lissencephaly: caused by failed neuronal migration during 3rd–4th months of development

2. Subcortical band heterotopia

3. Microcephaly: insufficient neuron proliferation.

What are the sensory cells of the Peripheral Nervous System (PNS) derived from?

They are derived from neural crest cells, which migrate away from the neural tube and differentiate into sensory neurons in response to growth cues from developing muscles.

What is the role of motor neurons in PNS development?

They act as “pathfinders”—creating axonal tracks that sensory neurons later follow for migration.

How are dorsal root ganglia formed?

Some neural crest cells migrate close to the dorsal spinal cord, differentiate into sensory neurons, and cluster to form dorsal root ganglia.

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Embryology

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