Korean, Edit

Chapter 7. Neuroembryology

Higher category : 【Biology】 Brain Science Index

1. 1^st. The formation of neural tube

⑴ 1^st - 1^st. Zygote becomes embryonic disc which consists of 3 germinal layers(endoderm, mesoderm, ectoderm) through “cleavage”.

⑵ 1^st - 2^nd. In the ectoderm, neurectoderm becomes thicker so that neurectoderm forms special cellular layers called “neural plate”.

⑶ 1^st - 3^rd. Diverticulation : Between neural plate and other ectoderm, there appears a crested structure called “neural crest”. (A)

① Neural crest : The tissue which differentiates from neurectoderm and doesn’t participate in constructing the neural plate.

Example : Meninges, etc.

⑷ 1^st - 4^th. Both lateral sides of neural plate becomes more crested, and there appears “neural groove”. (B)

⑸ 1^st - 5^th. Both sides of neural crest begin to combine, and later there appears a tube structure over the body without head and tail, which is called “neural tube”. (C)

① Anterior neuropore : The entrance of the neural tube at the head

② Posterior neuropore : The entrance of the neural tube at the tail

⑹ 1^st - 6^th. The neural tube becomes closed soon (from center to end). The lumen of the tube is called “central canal”.

① Notochord : It induces the closure of the neural tube in embryonic phase.

② If the closure doesn’t finish completely, the individual will have “anencephaly” or “spina bifida”.

⑺ 1^st - 7^th. Cells around the neural crest spread out and some of those cells make spinal ganglion. (D)

2. 2^nd. The proliferation of the neural tube

⑴ 2^nd - 1^st. Initially the total wall of the neural tube consists of a few layers of cells.

⑵ 2^nd - 2^nd. Cellular layers at the wall of the neural tube becomes thicker by cell proliferation.

⑶ 2^nd - 3^rd. These cellular layers form the “mantle

layer”, and the cells differentiate into neurons later.

⑷ 2^nd - 4^th. The neural fibers of the cells at the mantle layer extend and form the “marginal layer”.

⑸ 2^nd - 5^th. There appears the “neuroepithelial layer” at the inner surface of the neural tube, and it becomes “ependymal layer”.

⑹ 2^nd - 6^th. In the mantle layer, the front(ventral) neurons (in the basal plate) become motor neurons, and the back(dorsal) neurons (in the alar plate) become sensory neurons.

⑺ 2^nd - 7^th. The induced structure of the neural tube

① Spinal Cord

○ Alar Plate : Posterior Horn, Sensory Nuclei

○ Basal Plate : Anterior Horn, Motor Nuclei

② Medulla Oblongata

○ Alar Plate : General Somatic Afferent, Special Somatic Afferent, Visceral Afferent

○ Basal Plate : General Somatic Efferent, Special Somatic Efferent, General Visceral Efferent

③ Pons

○ Alar Plate : Tectal Structure

○ Basal Plate : Tegmentum(Central Tegmental Tract, Trapezoid Body), Basis Pontis(Griseum Pontis, Transverse Pontine Fiber, Corticospinal Tract)

④ Midbrain

○ Alar Plate : Tectum

○ Basal Plate : Cerebral Peduncle(Red Nucleus, Substantia Nigra, Crus Cerebri)

⑤ Diencephalon

○ Sulcus Limitans : Hypothalamic Sulcus

○ Alar Plate : Dorsal Thalamus

○ Basal Plate : Hypothalamus, Subthalamus, Zona Incerta

3. 3^rd. The formation and differentiation of the brain vesicle 

⑴ 3^rd - 1^st. The neural tube is divided 3 brain vesicles, “prosencephalon”(forebrain), “telencephalon”, and “rhombencephalon”(hindbrain)

⑵ 3^rd - 2^nd. Prosencephalon : It differentiates into “telencephalon”, “diencephalon”, etc.

① Telencephalon : It differentiates into “cerebral hemisphere”, basal ganglia, etc.

○ Basal ganglia : It differentiates into “corpus striatum”, “amygdala”, etc.

② Diencephalon : It differentiates into “thalamus”, etc.

○ Characteristics : It makes up the “limbic system”.

○ Thalamus differentiates into “dorsal thalamus”, “epithalamus”, “hypothalamus”, “subthalamus”, “metathalamus”, etc.

⑶ 3^rd - 3^rd. Mesencephalon : It differentiates into “midbrain”, etc.

① Characteristics : All the animal has it. The higher intelligence the entity has, the relatively smaller size mesencephalon has.

⑷ 3^rd - 4^th. Rhombencephalon : It differentiates into “metencephalon”, “myelencephalon”, etc.

① Characteristics : The higher intelligence the entity has, the more developed rhombencephalon is.

① Metencephalon : It differentiates into “cerebellum”, “pons”, etc.

② Myelencephalon : It differentiates into “medulla oblongata”, etc.

⑸ 3^rd - 5^th. Spinal cord : It has very slight change after embryo.

4. 4^th. The development of the primitive brain

⑴ 4^th - 1^st. The flexure formation

⑵ 4^th - 2^nd. The process of modification of brain

⑶ 4^th - 3^rd. The external form of the brain is completed within 8 weeks after fertilization. But it is not more than a water bag.

5. 5^th. The change of the wall of the neural tube (medulla oblongata)

⑴ 5^th - 1^st. The migration of the mantle layer and the marginal layer is observed “only” in medulla oblongata.

⑵ 5^th - 2^nd. The roof plate of medulla oblongata soon becomes indented.

6 6^th. The change of the wall of the neural tube (cerebellum) : The explanation focuses on the cerebellar process. This process generates the cortex structure(e.g., gyri, sulci).

⑴ 6^th - 1^st. Proliferation : The mantle layer cells are continuously proliferate.

⑵ 6^th - 2^nd. Migration : Half of the mantle layer cells migrate to the cortex.

① In fact, the mantle layer cells are also responsible for generating glial cells, the portion of migraing cells is less than half. The “half” is only available when the mantle layer cells only proliferate into the migrating neurons.

② 6^th - 2^nd - 1^st. The “radial glial cells” help the mantle layer cells migrate in a line.

③ 6^th - 2^nd - 2^nd. Granule cells, which are also neurons, migrate from the mantle layer to the spot right below the cortex and make new gray matters called “external granular layer”. (B, C)

④ 6^th - 2^nd - 3^rd. Granule cells remigrate inside in a little bit. 

○ It is the mechanism to form the molecular layer in which few cells exist.

⑤ 6^th - 2^nd - 4^th. Simultaneously, purkinje cells are created and migrate to the cerebellar cortex. (B, C) 

⑥ Inside-out Phenomenon : It refers that in the process of the embryonic cerebellum and the cerebrum, the next-turn migrating cells locate to the outside of the previous migrating cells. That is, the cells of the outer layer is generated in the end.

⑶ 6^th - 3^rd. Differentiation : The granule cells, the purkinje cells, and the mantle layer cells differentiate in place, and the mantle layer cells become “deep cerebellar nuclei”. (D)

① 6^th - 3^rd - 1^st. The migrating cells are small and lean so that they are optimized in migrating, so the migrated cells are larger than the migrating cells about 10 times.

⑷ 6^th - 4^th. Like above, the structures of both the cerebellum and the cerebrum become ‘basal ganglia’ → ‘medulla’ → ‘cortex’. 

① That is, nerve cell body - neural fiber(axon) - nerve cell body.

② That is, gray matter - white matter - gray matter.

⑸ The proliferation is ventricle-specific and the migration is CNS-specific.

7. 7^th. The partial expansion of the neural tube

⑴ The difference of the expansion of the neural tube ventricle causes various ventricles.

① Choroid Plexus : It secretes CSF(Cerebrospinal Fluid).

② CSF : It flows through Lateral Ventricle → 3^rd Ventricle → 4^th Ventricle.

⑵ Spinal cord : The ventricle preserve the natal shape of the primitive central canal, and is called “central canal” still.

⑶ Medulla oblongata and pons : The ventricle experiences considerable expansion and is called “4^th ventricle”.

⑷ Midbrain : The shape of the ventricle is analogous to that of the primitive central canal and is called “cerebral aqueduct”.

⑸ Diencephalon :  The ventricle has expanded, is located in the median plane, and is called “3^rd ventricle”.

⑹ Telencephalon : The ventricles have expanded, are located at each cerebral hemisphere one by one, and are called “lateral ventricles”.

⑺ Interventricular foramen : The 3^rd ventricle and the lateral ventricles are connected through interventricular foramen.

⑻ CSF(cerebrospinal fluid) : The fluid flows into the central canal and all the ventricles.

Input: 2018.09.15 23:51

1. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
2. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
3. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
4. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
5. Source : Seoul Nat’l University Medical College Prof. Jeong Cheon Gi, from Curriculum Handout
6. Source : Seoul Nat’l University Medical College Prof. Jeong Cheon Gi, from Curriculum Handout
7. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
8. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
9. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
10. Source : http://what-when-how.com/neuroscience/brainstem-iii-the-midbrain-organization-of-the-central-nervous-system-part-1/
11. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
12. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
13. Source : Seoul Nat’l University Medical College Prof. Hwang Yeong Il, from Curriculum Handout
14. Source : https://sites.google.com/a/wisc.edu/neuroradiology/anatomy/under-spin/ventricular-anatomy