Week 1 Flashcards
Developing triploblastic embryos have three germ layers:
- Ectoderm
- Mesoderm
- Endoderm
What areas of the body do these layers go on to make?
Ectoderm:
- Nervous system
- Skin
Endoderm:
- Gut
- Associated organs
Mesoderm:
- Muscle
- Skeleton
What is Gastrulation?
The transformation of a single-layered blastula into a multi-layered structure called a gastrula. It lays the foundation of the three primary germ layers
There are 3 crucial roles of gastrulation. What are they?
- Formation of the three germ layers in triploblastic organisms (ectoderm, mesoderm and endoderm)
- Setting up body axes (developed along two principle axes: dorsal-ventral and anterior-posterior)
- Specification of neural vs epidermal tissue (NEURAL INDUCTION)
What is neurulation?
Formation of the neural tube from the folding of the neural plate
The anterior-posterior axis is, at first, split into 3 primary vesicles: forebrain, midbrain and hindbrain (and the spinal cord)
The neural tube is then divided into 5 neuromeres. Match the areas to the parts of the nervous system they go on to develop into
a) Thalamus, Hypothalamus, Retina, Epithalamus
b) Pons and Cerebellum
c) Medulla
d) Spinal cord
e) Cerebral cortex, basal ganglia, hippocampal formation, amygdala, olfactory bulb
f) Midbrain
- Myelencephalon
- Diencephalon
- Telencephalon
- Mesencephalon
- Metencephalon
- Caudal part of the neural tube
a) Diencephalon
b) Metencephalon
c) Myelencephalon
d) Caudal part of the neural tube
e) Telencephalon
f) Mesencephalon
Its important to understand that this early patterning precedes the organisation of the adult nervous system
Describe the dorsal-ventral organisation of the spinal cord. Specifically to do with the position of the floor plate, roof plate, notochord, and interneurons
Additional bit on how its organised
- Roof plate close to the epidermis (roof plate)
- Floor plate by the notochord (ventral)
- The notochord sits underneath the neural tube
- V3 interneurons and Motor neurons are adjacent to the floor plate (Ventral side)
- Interneurons fill up rest of space between floor plate and roof plate
- The layout is organised by morphogens and concentration gradients (later lectures)
What is
a) Primary neurulation
b) Secondary neurulation
a) Primary
- Folding of the neural plate to form the neural tube
- Occurs in most vertebrates
b) Secondary
- The neural cells form a rod that extends along the anterior-posterior axis
- The actual neurulation is the formation of a cavity within the neural rod
What are 2 conditions that stem from improper neural tube formations
- Anencephaly: lack of proper brain formation
- Spina Bifida: Failure to close the neural tube
The Neural Crest:
The neural crest is considered the fourth germ layer. NC cells form the a) (anterior / lateral) edges of the neural plate and go on to form the b) (peripheral / central) nervous system. They are formed on the c) (dorsal / ventral) side of the neural tube and migrate inwards.
a) lateral
b) peripheral
c) dorsal
Both neural and non-neural cells are derived from the trunk neural crest.
There are 3 types of neural cells and 2 non-neural cell types. What are they?
Neural cells:
- Cranial neurons of the dorsal root and sympathetic ganglia (periph nervous system)
- Enteric neurons
- Schwann cells
Non-neuronal:
- Adrenal medulla
- Melanocytes
Describe some of the important features of C.elegans as a model organism to help understand the development of the brain / neural system
- Development completed rapidly in 2-3 days
- C. elegans is transparent
- Precisely known anatomy
- Development is highly stereotypical and all cell divisions are known
- Many genes in C. elegans have functional counterparts in humans and biochemical pathways are often conserved
The Development of the Drosophila Embryo:
- During gastrulation, mesodermal cells migrate into the a) (exterior/interior) and neuroectodermal cells become located at the b)(ventral/dorsal) midline
- During CNS formation, neuroectodermal cells delaminate from the c)(mesoderm/ectoderm)
Development of CIRCUITRY: - Ganglion Mother Cells (GMCs) and their neuronal and glial progenies form the nerve chord
- Longitudinal fascicles run along the anterior/posterior axis and connect anterior and posterior neurons
- Commissures run d) (parallel/perpendicular) to the fascicles and connect neurons from both halves of the embryo
a) interior
b) ventral
c) ectoderm
d) perpendicular
Why is Drosophila used as a model organism to study neural development?
- Life cycle of 2 weeks and is cheap and easy to breed
- Well established genetics allowing forward and reverse genetic approaches
- Screens easily performed
- Drosophila genome contains 17000 genes, ~50% homologues in humans
- Drosophila is being increasingly used as a model organism to study human disease
What are 4 examples of vertebrate models that can be used to study neural development?
- Xenopus
- Chicken
- Zebrafish
- Mouse
Why is the Xenopus used as a model organism?
And what is one problem with using them as model organisms?
- Xenopus produces large robust eggs which are easily accessible (microsurgery experiments, injection of molecules)
- Xenopus has provided many insights into early nervous system development
- Xenopus is tetraploid (contains 4 copies of genes)
- Takes females many months to reach maturity making genetic approaches hard
