Head and Neck Flashcards
Cells receive and process information from their surroundings such as…
extracellular matrix, secreted molecules (growth factors) from other cells, hormones, contact with other cells (tension), nutrients, oxygen levels, etc.
What defines the identity of each cell? (its appearance and how it behaves)
the complement of RNA & protein
Morphogenesis is ______ & _______
coordinated & generative
______ provide the blueprint that ensures we all have a maxilla and mandible and an integrated oronasal cavity, etc
Genes
_________ and differences in these non-genetic ‘instructions’ determines everything about our phenotype.
Gene mutation
What is the difference between epithelia and mesenchyme?
epithelia - tightly packed
mesenchyme - loosley connected
What do the terms ectoderm, mesoderm, and endoderm relate to?
embryonic origin of cells
All aspects of the craniofacial complex are defined by what axes?
- Left-right
- Dorsal-ventral
- Anterior-posterior
Clinical treatments always consider:
- form (eg. tooth shape, spacing, number, cusp pattern)
- symmetry
because they are critical for function and esthetics.
When does the dorsal-ventral axis form?
the first three weeks
- apparent by blastocyst stage
What does the inner cell mass of the blasocyst give rise to?
embryo
When is anterior-posterior axis begin?
at the start of week 3
- with appearance of the primitive streak
What layers make up the bilaminar disc?
epiblast
hypoblast
Epiblastic cells converge at midline and…
ingress
*marks posterior end
What does the appearance of the primitive streak define?
defines A-P and L-R axes
The primitive streak furrow progresses along the midline through what process?
convergent extension
What causes the formation of the 2nd and 3rd germ layer?
cells of the epiblast layer migrate through the primitive streak to form mesoderm and endoderm
What process allows for the formation of mesoderm?
epithelial to mesenchyme transformation (EMT)
What process allows for formation of endoderm?
movement of epiblast to form the embryonic endoderm (both epithelia)
What germ layer proliferates more and why?
Greater proliferation of epiblast (ectoderm) because it also generates all mesoderm and embryonic endoderm
What end of the primitive streak is unique in appearance and function?
Anterior-most end (ventral side)
What imporant structure for anterior area of the primitive streak is conserved in all vertebrates?
the node
What is the node essential for?
- patterning and induction of embryonic cells (mesoderm and embryonic endoderm)
- establishment of the left-right symmetry
Factors secreted by cells of the Node induce anteriorly migrating mesoderm to form:
- the prechordal plate
- the notochord
What is the prechordal plate?
- most anterior region of mesoderm
- provides the signals for induction of head structures
What is the notochord
- transient epithelial-like rod structure along the midline.
- provides the signals for induction of the neural plate
What structure provides the signals for induction of the head?
the prechordal plate
What structure provides the signals for induction of the neural plate?
the notochord
What allows for the creation of asymmetry in the once symmetrical embryo?
the node
What induces and specifies the fate of the mesoderm as it is formed?
the node
What allows the node to establish molecular asymmetry?
asymmetric expression of morphogenetic factors
- initiates cascade of gene expression to promote asymmetric specialization / commitment of mesoderm
Nodal cells each have one ____ to cause a rotational beat?
motile cilium
What is a cilium?
a membrane covered extension from the cell that has a microtubule cytoskeleton core
- can be mechanosensory or rotational
*nodal cilia are rotational
What does the rotational beat of nodal cilia allow for?
generates leftward flow, resulting in asymmetric distribution of morphogens / growth factors
Are reproducible morphological & functional asymmetries in nearly all internal organs?
yes
What can cause an effect on L-R symmetry?
cilia function affected; gene expression around node changes
1 in _________ people with situs inversus (normal health)
8500-10000
Is partial situs deleterious?
yes
What is the precursor to brain & spinal cord?
neural tube
Factors from the mesoderm
induce thickening of overlying ________
ectoderm
- creates neural plate
Signals from notochord induce a
__________ to help drive folding
‘hinge’ point
D-V patterning of neurons begins when?
the notochord induces folding
The anterior end of the neural tube has an expanded neural plate for what reason?
the future brain
Closure of neural tube proceeds in what direction?
anteriorly and posteriorly from mid-region
By end of week 3, head & neck
region comprises ______ of
embryo
half
What are the different defects in neural tube closure?
- spina bifida (open or closed) *most common
- iniencephaly
- anencephaly
- craniorachischisis
- encephalocele
The _________ membrane serves as
the hinge point during cephalization
oropharyngeal
What does folding of the embryo create?
- Concomitant with formation of
pharyngeal arches (> face & neck) - Foregut and hindgut specialization
What are the neural crest cells?
a unique population of (pluripotent) stem-like cells originating at the ‘crest’ of the enclosing neural tube
What way do the neural crest cells migrate?
Migrate ‘ventro-laterally’ to populate the ventral side of the embryo
What process generates the neural crest cells?
epithelial-mesenchymal
transformation (EMT)
*analogous to generating mesoderm
epithelial-mesenchymal
transformation (EMT) is also a common feature of what?
cancer
What do cranial neural crest cells do?
migration drives outgrowth of the primitive tissue masses that will form much of the head and neck
*unique in developmental potential (distinct from other neural crest cells)
What allows for the “second wave” of development?
cranial neural crest cells
What is the major contributor to craniofacial structure, and specifically to mineralized tissues of the oral region?
cranial neural crest cells
What are the derivatives of the cranial neural crest cells?
- sensory nervous system
- autonomic nervous system
- pigment cells
- endocrine cells
- skeleton
- connective tissue
- muscle
*last 3 are CNCC specific
CNCC fate determined prior to departure from the ___________
neural tube
*have positional identities
What are the visible constrictions in the neural tube?
rhombomeres 1-8, the diencephalon and anterior mesencephalon
*define distinct populations of CNCC and their route of migration into early facial tissue
What defines the reproducible paths of migration for the cranial neural crest cells?
mesoderm
What is coordinated morphogenesis?
early molecular patterning enables later coordinated tissue morphogenesis
What type of process is embryogenesis?
generative
Malformation and normal phenotypic variation can result from:
- single changes in gene sequence
- combinations of ‘normal’ gene variants
- changes in the ‘environment’ to which cells respond
