neural crest cells - 1 / orthodontic courses by indian dental academy

Neural Crest Cells INDIAN DENTAL ACADEMY

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“He who sees things grow from the beginning will have the finest view of them”

-Aristotle


FertilizationIt is sequence of events that begins with contact between a sperm and a oocyte and finally ends with the fusion of nuclei of the sperm and ovum and the intermingling of maternal and paternal chromosomes.

Zygotewww.indiandentalacademy.com

Cleavage It is a process by which zygote undergoes a series of rapid mitotic division.

First the zygote divides into two cells known as Blastomeres


Zygote showing the process of cleavage


Time: The division starts 30 hours after fertilization.Site: This occurs as the zygote passes along the uterine tube towards the uterus.


Important point:

There is increase in the number of cell without an increase in the cytoplasmic mass as a result of which cells progressively become smaller in size.


Morula

This is so called when the number of cells becomes 16

Time: 3-4 days after fertilizations

Site: Uterus www.indiandentalacademy.co

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Morula


BLASTOCYSTSpace appear between the central Blastomeres of Morula. This space gets filled with the fluid from the uterine cavity.

Trophoblast

Inner cell mass


Blastocyst


BLASTOCYSTFollowing this fluid – filled spaces fuse to form a single, large blastocyst cavity.

Blastocyst


Implantation Time: After six days

The blastocyst attaches itself to the endometrial epithelium, adjacent t the inner cell mass

Embryonic polewww.indiandentalacademy.co

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ImplantationAs this occurs the trophoblast start proliferating rapidly

cytotrophoblast syncytiotrophoblast


Implantation of the blastocyst


ImplantationFinger like processes of syncytiotrophoblast extend through the endometrial epithelium Time:by the end of the first week blastocyst superficially implants in the endometrium.Also a flattened layer of cells called hypoblast appear on the surface of the inner cell mass.www.indiandentalacademy.co

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Completion of implantationTime: the process of implantation is completed by the end of second week.

As the blastocyst slowly embeds itself in the endometrium trophoblast goes on differentiating into the two cell layer.


Formation of the amniotic cavity

As the implantation is progressing small cavity appears at the embryonic pole between embryoblast and trophoblast.This space forms the primodium of the amniotic cavity.


Developing amniotic cavity


Formation of Bilaminar plate

At the same time morphologic changes occur in the embryoblast resulting in the formation of circular,bilaminar plate of the cells called embryonic disc

epiblast hypoblast


Bilaminar plate


Formation of the primary yolk sac

Few cells from the hypoblast migrate to form a membrane called exocoelomic membrane This membrane surrounds the blastocyst cavity called exocoelomic cavity.

Primary yolk cellwww.indiandentalacademy.com

Primary yolk sac


Formation of the secondary yolk cell

Some cells from the hypoblast gives rise to a layer of loosely arranged tissue called-extra embryonic mesoderm.

Extra embryonic coelom

yolk sacwww.indiandentalacademy.com

Development of the secondary yolk sac


Development of chorionic sac

Extra embryonic coelom splits the extra embryonic mesoderm into two layers

Extraembryonic Somatic mesoderm

ExtraembryonicSplanchic mesoderm


Development of chorionic sac

Extra embryonic Somatic mesoderm+

Two layers of trophoblast

Chorionwww.indiandentalacademy.co

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Chorionic sac


Prochodral plate Time:around the 14th day few hypoblastic cells change into columnar shape and form a thickened ,circular area

Prochodral plate . www.indiandentalacademy.co

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Prochodral plate


The third weekGastrulation.Primitive streak.The notochordal process.Notochord.Neuralation.The neural crest cells.


Gastrulation

It is process by which the bilaminar embryonic disc is converted into a trilaminar embryonic disc resulting in the formation of the three germ layers and the primitive streak.


Primitive streakIt is a thickened linear band of epiblast which appears caudally in the median plane and on the dorsal aspect of the embryonic disc.

Primitive node

Primitive pitwww.indiandentalacademy.co

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Primitive node


Germ layersMesoblast/Mesenchyme--mesoderm

Primitive streak cell displace hypoblast -- endoderm

Epiblast -- ectoderm


Developing germ layers


Notochordal processSome mesenchymal cells migrate cranially from the primitive node to form a median cellular cord known as notochordal process

notochordal canalwww.indiandentalacademy.co

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The notochordal processprochordal plate

Notochordal canal

cloacal membranewww.indiandentalacademy.co

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Formation of the notochordIt is a cellular rod that develops by transformation of notochordal process

- defines the primitive axis of embryo - gives rigidity - future site of vertebral column.


Formation of the notochord1. As notochordal process

elongates ,notochordal canal extends cranially from primitive node to prochordal plate .

2. Floor of the notochordal process fuses with the underlying embryonic endoderm.

3. Fused region gradually undergo degeneration creating an opening.


Developing notochord


Formation of the notochord4. The opening rapidly becomes

confluent and notochordal canal disappears .

5. Beginning at cranial end ,notochordal plate infolds to form notochord.

6. The notochord finally detached from the embryonic endoderm.


NeuralationIt is process involved in the formation of the neural plate and neural folds and the closure of these folds to form the neural tube.

Neurlawww.indiandentalacademy.co

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Neural plate As the notochord develops ,embryonic ectoderm over it thickens to form the neural plate-neuroectoderm. Around the 18th day

Neural tubewww.indiandentalacademy.com

The neural crestSome neuroectodermal cells lying along the crest of each neural fold lose their epithelial affinities and are called neural crest cells.These form a irregular flattened mass called neural crest .


Characteristics of the neural crest cells

I. Pleuripotent capability –is the ability of these cells to give rise to several precursor cell.

II. Migratory property-Ncc break free from neural folds by losing their lateral connections to adjacent epidermal and neuroectodermal cells.



Migration

Active Passive

Without the With the ectoderm ectoderm


Factors affecting migration1. Extra cellular molecules- such as

fibronectin are encountered along the way of migration are used by Ncc to govern their path(Rovasio et.al.1983).

2. Vitamin A –slows the migration - acts as a teratogen


Factors affecting migration

3) Drugs-isotretenion(13-cis-retinoic acid)cause sever malformations by affecting the neural crest cell migration.



III. Regulation- reffers to the ability of an embryo to compensate for the loss of cells . - migration of the Ncc across the midline. - by increase proliferation of the remaining Ncc.


Study done by Bonner-Fraser(1986)

CSAT antibody was used Antibody was injected in embryonic chicks just before the initiation of the Ncc migration.Results were observed after-

-24 hrs-36-48 hrs


Study done by Bonner-Fraser(1986)

24 hrs later--defective proliferation.-defective initiation of migration.-defective directionality of migration

36-48 hrs- - Ncc developed normally



IV. Cessation-reffers to the property of the Ncc to cease the process of migration once they reach the site of future craniofacial structure.

-type II collagen.


Structure derived by the neural crest cells

I. Connective tissue- - Ectomesenchyme of facial prominences and brachial arches.

- Bones and cartilages of facial visceral skeleton. - Dermis of face and neck - Stroma of salivary ,thymus ,thyroid, parathyroid and pituitary gland. - Corneal mesenchyme .

- Aortic arch arteries.www.indiandentalacademy.co

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-Dental papilla -Portions of periodontal ligament-Cementum

II. Muscle tissue- -Ciliary muscles -Covering connective tissue of branchial arch muscles



III. Nervous tissue- -Leptomeninges. -Schwan sheath cells.

IV. Sensory ganglia- -Autonomic ganglia. -Spinal dorsal root ganglia. -Sensory ganglia.

V. ANS- -Sympathetic ganglia. -Parasympathetic ganglia.



VI. Endocrine tissue- -Adrenomedullary cells -Calcitonin ‘c’ cells

-Carotid bodyVII. Pigment cells-

-Melanocytes-Melanophores


Dental context1. The initiation of the tooth formation.2. The determination of the tooth's

crown pattern.3. The initiation of dentinogenesis.4. The initiation of amelogenesis.5. The determination of the size,shape

and number of the tooth roots.6. The determination of the anatomy of

the dentogingival junction.www.indiandentalacademy.co

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Clinical implications

1. Treachers Collins syndrome.

2. Hemifacial Microsomia.

3. Limb abnormalities.


Treachers Collins Syndrome


Hemifacial Microsomia


Summary of events Zygote

Morula

Blastula

Implantation

Amniotic cavitywww.indiandentalacademy.com

Summary of events Bilaminar embryonic disc

Yolk sac

Chorionic sac

Germ layers

Primitive streak www.indiandentalacademy.com

Summary of events Notochord

Neural plate and tube

Neural crest cells

Migration


References Contemporary Orthodontics-

William R ProffitThe Developing Human -

Moore and PersaudCraniofacial Morphogenesis and Dysmorphogenesis-

Katherine and AlphonseCraniofacial Embryology-

G.H.SperberOral histology-

Tencate www.indiandentalacademy.com

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neural crest cells - 1 / orthodontic courses by indian dental academy

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