Upload
indian-dental-academy
View
214
Download
0
Embed Size (px)
Citation preview
Neural Crest Cells INDIAN DENTAL ACADEMY
Leader in continuing dental education www.indiandentalacademy.com
www.indiandentalacademy.com
“He who sees things grow from the beginning will have the finest view of them”
-Aristotle
www.indiandentalacademy.com
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
www.indiandentalacademy.com
Zygote showing the process of cleavage
www.indiandentalacademy.com
Time: The division starts 30 hours after fertilization.Site: This occurs as the zygote passes along the uterine tube towards the uterus.
www.indiandentalacademy.com
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
Morula
This is so called when the number of cells becomes 16
Time: 3-4 days after fertilizations
Site: Uterus www.indiandentalacademy.co
m
Morula
www.indiandentalacademy.com
BLASTOCYSTSpace appear between the central Blastomeres of Morula. This space gets filled with the fluid from the uterine cavity.
Trophoblast
Inner cell mass
www.indiandentalacademy.com
Blastocyst
www.indiandentalacademy.com
BLASTOCYSTFollowing this fluid – filled spaces fuse to form a single, large blastocyst cavity.
Blastocyst
www.indiandentalacademy.com
Implantation Time: After six days
The blastocyst attaches itself to the endometrial epithelium, adjacent t the inner cell mass
Embryonic polewww.indiandentalacademy.co
m
ImplantationAs this occurs the trophoblast start proliferating rapidly
cytotrophoblast syncytiotrophoblast
www.indiandentalacademy.com
Implantation of the blastocyst
www.indiandentalacademy.com
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
m
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.
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
Developing amniotic cavity
www.indiandentalacademy.com
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
www.indiandentalacademy.com
Bilaminar plate
www.indiandentalacademy.com
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
www.indiandentalacademy.com
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
www.indiandentalacademy.com
Development of chorionic sac
Extra embryonic coelom splits the extra embryonic mesoderm into two layers
Extraembryonic Somatic mesoderm
ExtraembryonicSplanchic mesoderm
www.indiandentalacademy.com
Development of chorionic sac
Extra embryonic Somatic mesoderm+
Two layers of trophoblast
Chorionwww.indiandentalacademy.co
m
Chorionic sac
www.indiandentalacademy.com
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
m
Prochodral plate
www.indiandentalacademy.com
The third weekGastrulation.Primitive streak.The notochordal process.Notochord.Neuralation.The neural crest cells.
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
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
m
Primitive node
www.indiandentalacademy.com
Germ layersMesoblast/Mesenchyme--mesoderm
Primitive streak cell displace hypoblast -- endoderm
Epiblast -- ectoderm
www.indiandentalacademy.com
Developing germ layers
www.indiandentalacademy.com
Notochordal processSome mesenchymal cells migrate cranially from the primitive node to form a median cellular cord known as notochordal process
notochordal canalwww.indiandentalacademy.co
m
The notochordal processprochordal plate
Notochordal canal
cloacal membranewww.indiandentalacademy.co
m
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.
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
Developing notochord
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
www.indiandentalacademy.com
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
m
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
www.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 .
www.indiandentalacademy.com
www.indiandentalacademy.com
www.indiandentalacademy.com
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.
www.indiandentalacademy.com
Characteristics of the neural crest cells
Migration
Active Passive
Without the With the ectoderm ectoderm
www.indiandentalacademy.com
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
www.indiandentalacademy.com
Factors affecting migration
3) Drugs-isotretenion(13-cis-retinoic acid)cause sever malformations by affecting the neural crest cell migration.
www.indiandentalacademy.com
Characteristics of the neural crest cells
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.
www.indiandentalacademy.com
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
www.indiandentalacademy.com
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
www.indiandentalacademy.com
Characteristics of the neural crest cells
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.
www.indiandentalacademy.com
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
m
Structure derived by the neural crest cells
-Dental papilla -Portions of periodontal ligament-Cementum
II. Muscle tissue- -Ciliary muscles -Covering connective tissue of branchial arch muscles
www.indiandentalacademy.com
Structure derived by the neural crest cells
III. Nervous tissue- -Leptomeninges. -Schwan sheath cells.
IV. Sensory ganglia- -Autonomic ganglia. -Spinal dorsal root ganglia. -Sensory ganglia.
V. ANS- -Sympathetic ganglia. -Parasympathetic ganglia.
www.indiandentalacademy.com
Structure derived by the neural crest cells
VI. Endocrine tissue- -Adrenomedullary cells -Calcitonin ‘c’ cells
-Carotid bodyVII. Pigment cells-
-Melanocytes-Melanophores
www.indiandentalacademy.com
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
m
Clinical implications
1. Treachers Collins syndrome.
2. Hemifacial Microsomia.
3. Limb abnormalities.
www.indiandentalacademy.com
Treachers Collins Syndrome
www.indiandentalacademy.com
Hemifacial Microsomia
www.indiandentalacademy.com
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
www.indiandentalacademy.com
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
Thank you
For more details please visit www.indiandentalacademy.com
www.indiandentalacademy.com