Head & Neck Development Flashcards
Dr. Timothy Cox
Morphogenesis of the head and neck is a _____ process, NOT a _____ process
Generative; descriptive
Encode RNA & proteins:
Genes (DNA)
The complement of RNA & proteins produced defines the ______; meaning its appearance and how it behaves
Identity of each cell
Provides the blueprint that ensures we all have a maxilla & mandible & an integrated oronasal cavity:
Genes (genome)
Gene mutations & differences in non-genetic instructions determines everything about:
Phenotype
Cells that are tightly compact, & tightly bound together. often found in sheets within the body & have a very distinct sort of shape; not very mobile:
Epithelia
Cells that are loosely connected, surrounded by many types of extracellular matrix so they can move around in the body because they are not attached to anything; they can receive and move towards signals:
Mesenchyme
Outer cell layer
Ectoderm
Middle cell layer:
Mesoderm
Inner cell layer:
Endoderm
The terms ecto-, endo- & mesoderm are related to the:
Embryonic origin of cells
All aspects of the craniofacial complex are defined by axes: (3)
- Left-right
- Dorsal-ventral
- Anterior-posterior
Clinical treatments always consider _____ & ____ because the are critical for function & esthetics
Form & Symmetry
Tooth shape, spacing, number & cusp pattern are all examples of:
Form
In a clinical aspect, form and symmetry are always considered because:
They are critical for function & esthetics
Axis that becomes apparent by the blastocyst stage:
Dorsal-ventral axis
When does the dorsal-ventral axis become apparent?
Blastocyst stage
At the 4-cell stage of development, what structures do we see?
Blastomeres
The 32-cell stage in which we still just see a ball of cells:
morula
Once we reach the 32-cell stage and the morula is formed, the cells start to undergo a process called:
Compaction
During first three weeks of development the cells within the outer coating (which are called the zona pellucida) undergo some sort of specialization to create an outer lining of cells called the:
Ectodermal cell layer
During the first three weeks of development when compaction takes place, the cells of the zona pellucida become the ectodermal cell layer, while the cells in the middle become the:
Inner cell mass
During the first three weeks of developement, the cells that comprise the inner cell mass will give rise to the _____
Embryo
During the first three weeks of development, the cells that comprise the inner cell mass that go on to become the embryo itself are also referred to as _____ because:
Embryonic stem cells; they give rise to every organ & tissue in the human body
Following fertilization, the zygote (single cell) undergoes _____ cell divisions to result in a total of _____ cells just prior to implantation
6 cell divisions; 64 cells
During the first three weeks of development, the morula undergoes compaction to form the ectodermal cell layer, & the inner cell mass. What else is formed during this point in development?
Left over space to form a cavity
Once the morula undergoes compaction to form an ectodermal cell layer, an inner cell mass and a cavity of space, it is now considered:
Blastocyst
With the formation of the blastocyst, we can see that everything practically hatches from the _____ as it passes down the fallopian tubes:
Zona pellucida
What process occurs following the formation of a blastocyst?
Implantation
Once implantation into the uterus occurs, this sets off a series of:
More specialized differentiations
After implantation, around the third week of development, the more specialized differentiations lead to:
Specification of the germ layers
What are the germ layers that are formed following implantation, around the third week of development?
Ectoderm
Endoderm
Mesoderm
The inner cell mass leads to:
Embryonic stem cells
Anterior-posterior axis (head-tail) and left-right axis determined at the start of _____ with the appearance of the _____
Week 3; primitive streak
Two-layered epithelial disc; the region between where the ectoderm & endoderm contact:
Bilaminar disc
The bilaminar disc is location in which the ________ will form from
Embryo proper
Ectodermal layer of the bilaminar disc:
Epiblast
Endoderm layer of the bilaminar disc:
Hypoblast
Layer of the bilaminar disc that will form the entirety of the embryo:
Epiblast
One of the first things we will see on the bilaminar disc is a:
Invagination of cells that converge at the midline
What happens to the epiblastic cells at the midline of the bilaminar disc?
Converge at midline & ingress
Once the epiblastic cells at the midline of the bilaminar disc converge and ingress this marks:
The posterior end
When does the primitive streak start to appear?
Around day 15
When is the posterior end of the embryo determined?
Around day 15 with the primitive streak formation
Invagination of epiblastic cells that marks the posterior end of the embryo, therefore defining the anterior-posterior axis:
Primitive streak
Once the primitive streak is forming, defining the anterior-posterior axis, you essentially will have:
A left-right axis
Looking down at the embryo at the bilaminar disc, the endoderm forms the ______ while the ectoderm forms the _______
Endoderm= yolk sac
Ectoderm= Amniotic cavity
The furrow of the primitive streak progressively elongates along the midline through the process of:
Convergent extension
Describe the path direction of formation of the primitive streak:
Starts on posterior end & moves anteriorly
When you have tightly bound epithelial cells on either side of the primitive streak and these cells start to proliferate and grow. As they come together at the midline they have to work out how to deal with these extra cells that are all pushing together. The result is the intertwining of cells.
This process is called:
Convergent extension
The process of convergent extension causes the expansion of the _____ length of the embryo:
Anterior-posterior
Convergence may also be called _____
Intercalation
Convergence/intercalation results in:
Embryoelongation (extension)
Cells of the epiblast (layer 1) migrate through the primitive streak to form _____ & _____
Mesoderm & embryonic (gut) endoderm
The start to forming the inner tissue of the embryo occurs through the process:
Gastrulation
Formation of the second & third germ layer occur through:
Gastrulation
Gastrulation occurs through the process of ________ to form mesoderm:
Epithelial to mesenchyme transformation (EMT)
During the process of gastrulation, the movement of epiblast (ectoderm) occurs to form _________ (both epithelia)
Embryonic endoderm
Describe the growth of the germ layers:
Disproportionate growth
The growth of the germ layers can be described as disproportionate, why is this?
Greater proliferation of the epiblast (ectoderm) because it also generate all the mesoderm & embryonic endoderm
As the germ layers are being formed, the generated (proliferating) mesoderm migrates:
Toward anterior (head) end
When the mesoderm is being driven forward, it receives information that tells it to start forming structures, this is the key process of:
Head formation
The primitive streak ends in an asymmetric bulge called the:
Node
The anterior-most end (ventral side) of the primitive streak is unique in both:
Appearance & function
The node may also be called the:
Organizer
The node (organizer) is a _______ structure across _____
Conserved; all vertebrates
Describe what the node is essential for:
- Patterning & induction of embryonic cells (mesoderm & embryonic endoderm)
- Establishment of L-R symmetry of organs
Factors secreted by cells of the node induce anteriorly migrating mesoderm to form:
- The prechordal plate
- The notochord
Factors secreted by the cells of the nude induce _________ to form the prechordal plate & the notochord
Anteriorly migrating mesoderm
What forms first, the prechordal plate or the notochord?
Prechordal plate
Forms from the most anterior region of mesoderm & provides the signals for the induction of head structures:
Prechordal plate
The prechordal plate provides:
The signals for the induction of head structures
Transient epithelial-like rod structure along the midline that provides the signals for induction of the neural plate:
Notochord
Describe the locational relationship between the notochord and prechordal plate:
The notochord is just anterior to the prechordal plate
The notochord provides:
The signals for the induction of the neural plate
The neural plate is formed from the ______ and ultimately gives rise to the _____
Overlying ectoderm; spinal cord
The node induces the _______
Body axis
Provides signals to specify the fate of the mesoderm passing by the node:
The node
The node is responsible for inducing & specifying the fate of the ____ as its formed
Mesoderm
Responsible for the creation of aymmetry in the symmetrical embyro
The node
Explain how the node is responsible for the creation of asymmetry in the symmetrical embryo:
First establishes molecular asymmetric which is converted into asymmetric organogenesis
Establishing molecular asymmetry occurs the:
Asymmetric expression of morphogenetic factors around the node
Give examples of morphogenetic factors are expressed in an asymmetric manner in order to establish molecular asymmetry:
-SHH
-BMP4
-FGF8
Asymmetric expression of morphogenetic factors around the node initiates a ______ to promote ______
Cascade of gene expression; asymmetric specialization/commitment of mesoderm
The node generates _____
Asymmetry
Nodal cells each have:
One motile cilium
A membrane covered extension fro the cell that has a microtubule cytoskeleton core which helps define its properties
Cilium
The properties of the cilium may be _____ or _____
-Mechanosensory
-Rotational
Cilium can be a site where _______ are secreted from
Growth factors
Describe the properties of the cilium on the cells of the node:
Rotational
Nodal cilia have a _______ (for a few hours only)
Rotational beat
The rotational beat of the nodal cilia generates ______
Leftward flow
The rotational beat of the nodal cilia generates a leftward flow, resulting in:
Asymmetric distribution of morphogens/growth factors
Describe what is meant by saying the nodal cilia have a rotational beat:
They all rotate in the same direction
In nearly all internal organs their are __________, that is an evolutionarily conserved mechanism in vertebrates
Reproducible morphological & functional asymmetries
In mice, there are _____ genes that affect L-R asymmetry
27 genes
Explain how the 27 genes in mice affect L-R asymmetry:
Cilia function affected; gene expression around node changes
The normal arrangement of internal organs:
Situs solitus
Where all organs are on the complete opposite side of the body; however health is normal
Situs inversus
Partial situs can be ______
Deleterious
The process of neural tube formation:
Neurulation
Neurulation is a key aspect of development for setting up the:
Head & neck
The neural tube is the precursor to the:
Brain & spinal cord
During gastrulation, you have mesoderm forming between ectoderm & endoderm and the formation of a _______ along the length of the embryo as a result of nodal signaling
Notochord
Signals from the notocord lead to the cells in the ectoderm to start to thicken, enlarge, & form a slightly different appearace to the regular ectoderm, this is called:
The neural plate
As the notochord keeps on signaling, the cells closest to the notochord change shape and that allows for:
The neural plate to fold
When factors from the mesoderm induce thickening of the overlying ectoderm this results in the:
Neural plate
Signals from the notochord induce a _____ to help drive folding
Hinge point
As the neural plate continues to get signals for folding this ultimately results in:
Formation of the neural tube
The morphological difference of the anterior-most region of the neural tube reflects ________ and thus _______
Unique underyling cellular identities; different inductive cues
Transcription factor expressed in anterior visceral endoderm that contributes to anterior (head) specification:
Lim1 gene
The advance maturity of the anterior end of the neural plate leads to:
Expansion of the neural plate
The expanded portion of the neural plate ultimately gives rise to the:
Future brain
Describe the directionality of the neural tube closure:
Closure of the neural tube proceeds anteriorly & posteriorly from mid-region
(posteriorly over the tail)
(anteriorly over the brain)
By the end of week 3 the head & neck region comprises around:
Half of the embryo
-Anencephaly
-Craniorachischisis
-Open spina bifida
-Closed spina bifida
-Encephalocele
-Iniencephaly
What do all of these have in common?
Caused by defects in neural tube closure
When a small portion of the neural tube doesn’t close off in the spinal cord region, resulting in exposed spinal fluid and leakage:
Open spina bifida
Caused by a defect in neural tube closure that results in this common, viable condition:
Spina bifida
Failure of closure of the neural tube at the ____ end often results in more severe defects like an encephalocele:
Anterior end
The whole process of head formation that occurs while the neural tube is growing & trying to close off:
Cephalization
At the very anterior end of the neural tube, the midline region where ectodern & endoderm contact eachother directly with no mesoderm in between:
Oropharyngeal membrane
The orpharyngeal membrane is important for ______ and provides a hingepoint for folding at the anterior end:
facial development
The mesoderm that is around the oropharyngeal membrane region forms the:
Cardiac tissue
The oropharyngeal membrane serves as the ______ during cephalization
Hinge point
Folding of the whole embryo occurs while ____ occurs
Cephalization
Folding of the whole embryo while cephalization occurs is cocomitant with the formation of:
pharyngeal arches
The pharyngeal arches give rise to:
The face & neck
What other type of specialization occurs along with folding of the whole embryo?
Foregut & hindgut specialization
The process of neural tube developement gives rise to a unique population of pluripotent stem-like cells called:
Neural crest cells
The unique population of pluripotent stem-like cells that are created during the process of neural tube development originate at:
The CREST of the enclosing neural tube
Neural crest cells migrate ____ to populate the _____ side of the embryo
Ventro-laterally; ventral
Neural crest cells differentiate into:
A wide variety of cell types/tissues
Neural crest cells are generated by a process of _______ that is analogous to that of generating the third germ layer
Epithelial-mesenchymal transformation (EMT)
During gastrulation the neural cells go from a ________ phenotype to a ______ phenotype
Ectodermal —> Mesenchymal
Conversion from an epithelial phenotype to a mesenchymal (highly motile) phenotype:
EMT
Population of neural crest cells that give rise to craniofacial structures, migrate extensively & drive outgrowth of the primitive tissue masses that will form much of the head & neck:
Cranial neural crest cells
Cranial neural crest cell migration drives outgrowth of the _____ tissue that will form much of the ____ & ____
primitive tissue; head & neck
Cranial neural crest cells are unique in:
Developmental potential
Cranial neural crest cell migration driving outgrowth of primitive tissue can be considered:
A second wave of development
Major contributor to craniofacial structure and specifically to mineralized tissues of the oral region:
Cranial neural crest cells
Major derivatives of neural crest cells include:
CNCC-Specific tissue contributions include:
- Sensory nervous system
- Autonomic nervous system
- Pigment cells
- Endocrine & paracrine cells
- Mesectodermal cells including
-skeleton
-connective tissue
-mnuscle
CNCC fate is determined:
Prior to departure from neural tube
CNCC have ______ identities
Positional
We can see multiple visible constrictions in the neural tube called _____
Rhobomeres
Describe the multiple visible constrictions seen in the neural tube:
- Rhombomeres 1-8
- the diencephalon
- the anterior mesencephalon
The multiple visible constrictions seen in the neural tube define distinct populations of _____ and their ______ into early facial tissue
CNCC; route of migration
What is unique to the cranial neural crest cells of each rhombomere on the neural tube?
Their patterns of gene expression
The directed CNCC migration can be described as _____ paths of migration, defined by _____
Reproducible; mesoderm
Clusters of mesoderm:
Somites
Key takeaway from the process of morphogenesis of the head and neck, is that the process is:
HIGHLY coordinated
Early molecular patterning that occurs during gastrulation enables later:
Coordinated tissue morphogenesis
Embryogenesis is a _____ process of development, not a ______ process
Generative; descriptive
_______ & _______ can result from differences in the generative process of embryogenesis:
Malformation & Normal phenotypic variation
- Single changes in gene sequence
- Combination of ‘normal’ gene variants
- Changes in the ‘environment’ to which cells respond
These are all differences in the generative process of embryogenesis that can result in:
- Malformation
- Normal phenotypic variation
