Head & Neck Development

Question 1

Genes (DNA) encode (2)

Answer 1

RNA and proteins.

Question 2

The complement of RNA & protein produced defines the

Answer 2

identity of each cell – its appearance and how it behaves.

Question 3

Cells receive and process information from their surroundings – (6)

Answer 3

extracellular matrix, secreted molecules (growth factors) from other cells, hormones, contact with other cells (tension), nutrients, oxygen levels, etc.

Question 4

Cells receive and process information from their surroundings – extracellular matrix, secreted molecules (growth factors) from other cells, hormones, contact with other cells (tension), nutrients, oxygen levels, etc.
•These in turn modify the genes expressed, thus allowing the cell to

Answer 4

adapt to its situation and take on new properties / behaviors

Question 5

Genes (genome) provide the blueprint that ensures we all have a maxilla and mandible and an integrated oronasal cavity, etc. But gene mutation and differences in these non-genetic ‘instructions’ determines everything about our —.

Answer 5

phenotype

Question 6

All aspects of the craniofacial complex are defined by

axes: (3)

Answer 6

• Left-right
• Dorsal-ventral
• Anterior-posterior

Question 7

Clinical treatments always consider: (2)

Answer 7

• form (eg. tooth shape, spacing, number, cusp pattern), and

* symmetry because they are critical for function and esthetics.

Question 8

Dorsal-ventral axis

•apparent by — stage

Answer 8

blastocyst

Question 9

Is the D-V axis established as a consequence of cavitation and
formation of inner cell mass (ICM) or is it determined earlier?

Question 10

Anterior-posterior (A-P) axis [head-tail] and left-
right (L-R) axis determined at start of week 3, with
appearance of the

Answer 10

primitive streak

Question 11

Epiblastic cells converge at midline and ingress

marks — end

Answer 11

posterior

Question 12

The Primitive Streak
Appearance defines (2) axes

Answer 12

A-P and L-R

Question 13

Furrow progressively elongates along midline

•through process of

Answer 13

convergent extension

Question 14

Cells of the epiblast (layer 1) migrate through primitive

streak to form (2)

Answer 14

mesoderm & embryonic (gut) endoderm

Question 15

•through process of 
epithelial to 
mesenchyme 
transformation (EMT) 
to form ---

Answer 15

mesoderm

Question 16

Movement of
epiblast (ectoderm)
to form —- – both
epithelia

Answer 16

embryonic

endoderm

Question 17

Disproportionate — of the germ layers

Answer 17

growth

Question 18

Greater proliferation of
epiblast (ectoderm) because it
also generates all (2)

Answer 18

mesoderm

and embryonic endoderm.

Question 19

Anterior-most end (ventral side) of primitive streak is

unique in both

Answer 19

appearance and function

Question 20

The — (or Organizer) is a
conserved structure across all
vertebrates

Answer 20

Node

Question 21

the node is essential for (2)

Answer 21

•patterning and induction of embryonic cells
(mesoderm and embryonic endoderm)
•establishment of the left-right symmetry

Question 22

Factors secreted by cells of the Node induce

anteriorly migrating mesoderm to form: (2)

Answer 22

• the prechordal plate

* the notochord

Question 23

the prechordal plate (2)

Answer 23

• most anterior region of mesoderm

* provides the signals for induction of head structures

Question 24

the notochord (2)

Answer 24

• transient epithelial-like rod structure along the midline.

* provides the signals for induction of the neural plate

Question 25

The Node induces the

Answer 25

body axis

Question 26

The Node induces the body axis > Induce and specify the fate of the ---- as it is formed

Answer 26

mesoderm

Question 27

Creation of asymmetry in symmetrical embryo (2)

Answer 27

* First establishes molecular asymmetry | * Conversion into asymmetric organogenesis

Question 28

Establishing Molecular Asymmetry

Answer 28

``` Asymmetric expression of morphogenetic factors (eg. SHH, BMP4 & FGF8) around Node > initiates cascade of gene expression to promote asymmetric specialisation / commitment of mesoderm ```

Question 29

Nodal cells each have one

Answer 29

motile cilium

Question 30

A cilium is a membrane covered extension from the cell that has a microtubule cytoskeleton core which helps define the properties of the cilium: (2)

Answer 30

* mechanosensory, or | * rotational

Question 31

Nodal cilia have a rotational beat (for a few hours only) | •generates leftward flow, resulting in

Answer 31

asymmetric distribution of | morphogens / growth factors

Question 32

Reproducible morphological & functional asymmetries in | nearly all

Answer 32

internal organs. | >> Evolutionarily conserved mechanism in vertebrates

Question 33

In mice, ~-- genes affect L-R asymmetry

Answer 33

27 | >> cilia function affected; gene expression around Node changes

Question 34

Organ asymmetry 1 in --- people with situs inversus (normal health) > cf. partial situs which can be deleterious

Answer 34

8500-10000

Question 35

Factors from the mesoderm induce thickening of overlying ectoderm >>

Answer 35

neural plate

Question 36

``` Neurulation [Neural Tube Formation] precursor to (2) ```

Answer 36

brain | spinal cord

Question 37

Signals from notochord induce a ‘hinge’ point (floor plate) to help drive ---

Answer 37

folding

Question 38

The morphological difference of the anterior-most region of | the neural tube reflects

Answer 38

unique underlying cellular identities | and thus different inductive cues (secreted factors)

Question 39

Advanced maturity of anterior end > expanded neural plate | >>

Answer 39

future brain

Question 40

Closure of neural tube | proceeds

Answer 40

anteriorly and posteriorly from mid-region

Question 41

By end of week ---, head & neck region comprises ~half of embryo.

Answer 41

3

Question 42

The --- membrane serves as the hinge point during cephalization

Answer 42

oropharyngeal

Question 43

Embryonic Folding

Answer 43

Folding of whole embryo while | cephalization occurs

Question 44

``` Folding of whole embryo while cephalization occurs (2) ```

Answer 44

•Concomitant with formation of pharyngeal arches (> face & neck) •Foregut and hindgut specialization

Question 45

Neural Crest Cells

Answer 45

a unique population of (pluripotent) stem-like cells originating at the ‘crest’ of the enclosing neural tube. •Migrate ‘ventro-laterally’ to populate the ventral side of the embryo •Differentiate into a wide variety of cell types / tissues

Question 46

NCC generated by

Answer 46

process of epithelial-mesenchymal transformation (EMT) that is analogous to that generating the third germ layer (mesoderm)

Question 47

CNCC migration drives outgrowth of the primitive tissue | masses that will form much of the

Answer 47

head and neck

Question 48

Cranial Neural Crest Cells Unique in --- potential (distinct from other neural crest cells)

Answer 48

developmental

Question 49

Major contributor to craniofacial structure, and | specifically to

Answer 49

mineralized tissues of the oral region

Question 50

Rhombomeres & Cranial Patterning

Answer 50

CNCC fate determined prior to departure from neural tube | > ie. they have “positional identities”

Question 51

Multiple visible constrictions in neural tube (2)

Answer 51

•rhombomeres 1 - 8, the diencephalon and anterior mesencephalon •define distinct populations of CNCC and their route of migration into early facial tissue.

Question 52

Reproducible paths of migration | > defined by ---

Answer 52

mesoderm

Question 53

``` Directed CNCC Migration experiment: Pharyngeal arches 1, 2 & 3 are populated by NC cells from rhombomeres 2, 4 & 6, respectively. >> If r2 cells transplanted to r4 position, ```

Answer 53

migration still occurs through arch 2 - but cells differentiate into structures characteristic of arch 1!

Question 54

Early molecular patterning (est. during gastrulation) | enables later coordinated tissue ---.

Answer 54

morphogenesis

Question 55

Embryogenesis is a ‘---’ process | not descriptive

Answer 55

generative

Question 56

Malformation and normal phenotypic variation can result | from: (3)

Answer 56

* single changes in gene sequence * combinations of ‘normal’ gene variants, or * changes in the ‘environment’ to which cells respond