Chapter 9: The Emergence of Ectoderm Flashcards
Ectoderm forms:
vertebrate nervous system
epidermis
3 Major Domains
- Surface
- Neural Crest
- Neural Tube
Also known as epidermis; outer layer of skin
Surface
the region that connects the neural tube and the epidermis
Neural Crest
forms the brain and the spinal cord
Neural Tube
Part of the Surface
● epidermis
● hair
● sebaceous glands
● olfactory epithelium
● mouthepithelium
○ anterior pituitary
○ tooth enamel
○ cheek epithelium
● lens and cornea
Parts of the Neural Tube
● brain
● neural pituitary
● spinal cord
● motorneurons
● retina
It is a structure that serves as the basis for the nervous system
Neural Plate
A part of both digestive and respiratory system
Pharynx
4 Stages of Pluripotent Development into Neuroblast
Competence
Specification
Commitment
Differentiation
parts of Neural crest
● peripheral nervous system
○ schwann cells
○ neuroglial cells
○ sympathetic nervous system
○ parasympathetic nervous system
● adrenal medulla
● melanocytes
● facial cartilage
● dentine of teeth
- multipotent cells become neuroblast once they are exposed to the appropriate signals
- have the ability to response to the particular signals
Competence
→ the cells received the signals and successfully
develop into neuroblasts, but… progression along
the neural differentiation pathway repressed by
other signal
→ which means, that specification is a transition
between cells to become anything with their own
fates
Specification
→ the neuroblasts enter the neural differentiation
pathway and become neurons even in the presence
of signals
→cells will develop into neuroblasts and cannot be
reversed
Commitment
→ the neuroblasts leave the mitotic cycle and
express those genes characteristics of neurons
→ this is a process in which the unspecialized cells
become specialized to carry out distinct functions
Differentiation
2 Ways of Neural Tube Formation
a. Primary Neurulation
b. Secondary Neurulation
→ the cells surrounding the neural plate direct the
neural plate to proliferate, invaginate, and pinch off
the surface to form a hollow tube
→the formation of the neural tube direct came from
the ectoderm
Primary Neurulation
→ the neural tube arises from the coalescence of
mesenchyme cells into a solid cord that subsequently forms
cavities that coalesce to create a hollow tube
→ neural tube arises from mesenchyme cells underneath
the ectoderm
Secondary Neurulation
3 Sets of Cells in Ectoderm
● the internally positioned neural tube
● the externally positioned epidermis of the skin
● the neural crest
forms when the edges of neural plate thicken and move upward
Neural folds
appears in the center of the plate, dividing the future right and left sides of the embryo
Neural groove
4 Stages of Neurulation
- Formation and folding of the neural tube
- Shaping and elevation of the neural tube
- Convergence of the neural folds, creating a neural groove
- Closure of the neural groove to form the neural tube
important factor in shaping the neural plate
epidermis
→ shaped by the movements of the epidermal and neural plate regions
→neural plate lengthens along the anterior-posterior axis and narrows by convergent extension
→convergence and extension movements are
critical for shaping the neural plate
→in chick, divisions of the neural plate cells
are in the anterior-posterior, or break-tail,
direction
Formation and Shaping of Neural Plate
→bending of the neural plate involves the formation of hinge regions where the neural plate contacts surrounding tissue
Bending and Convergence of Neural Plate
in birds and mammals, the cells at the
midline of the neural plate forms the
medial hinge point (MHP)
→Primary Neurulation is regulated by two forces:
- Intrinsic wedging
- Extrinsic forces
occurs within cells of the hinge regions, bending the neural plate
Intrinsic wedging
the migration of the surface ectoderm
toward the center of the embryo
Extrinsic forces
