Unit 2 - Embryology Flashcards
What does the inner cell mass give rise to
Embryonic disc
Embryonic period
What is gastrulation
What is the inner cell mass converted to
Trilaminar embryonic disc and 4 extraembryonic membranes
The embryonic disc is composed of cells which develop to form the foetus
What does the mesoderm become
Muscle
Nervous tissue
Bone
What does the endoderm become
Internal organs of the body
Sagittal section of trilaminar disc about 16 days after fertilisation
Ectoderm, mesoderm and endoderm
2 structures formed at gastrulation
Primitive streak
Notochord
What is released from the notochord
Induction factors released from it and they stimulate the cells to form the groove (primitive streak)
What does the notochord induce
Specialisation of neural plate into neural groove
What is the neural plate
A thickened area of ectoderm
What develops from the neural plate
Longitudinal neural groove - neural folds on each side
How is the neural tube formed
Neural folds fuse in medial plane
Neural tube separate from surface ectoderm - beginning of brain and spinal cord
What signifies the beginning of the brain and spinal cord
Neural tube separates from surface ectoderm
When is neurulation complete
By end of week 4
What does the neural crest become
Future dorsal root ganglia, autonomic ganglia, pia/arachnoid mater
How does ancephaly develop
If the cranial and caudal ends of neural tube (neuropores) do not close
What happens to the neuropores at each end of neural tube
Where does the neural plate expand
They close
Neural plate expanded rostrally where brain will develop
Overview of neurulation
Overview of notochord and embryonic disc
Development of brain
Prosencephalon
Forebrain
Mesencephalon
Midbrain
Rhomboencephalon
Hindbrain
When do the 3 primary brain vesicles develop
@ 4 weeks
When do the secondary brain vesicles develop
5th week
TELENCEPHALON
Arises from
Becomes
Prosencephalon
Cerebrum
DIENCEPHALON
Arises from
Becomes
Derives from the prosencephalon
Becomes the thalamus, hypothalamus, epithalamus
MESENCEPHALON
Only primary vesicle that does not form a new secondary vesicle
METENCEPHALON
Arises from
Becomes
Rhomboencephalon
Pons & cerebellum
MYELENCEPHALON
Arises from
Becomes
Derives from rhomboencephalon (medulla oblongata)
Prosencephalon gives rise to
Telencephalon
Diencephalon
Rhomboencephalon gives rise to
Metencephalon
Myelencephalon
Overview of brain vesicles
Developing human brain
3 folds of the cranial neural tube
when does this occur
Weeks 4-8
Mesencephalic (cranial/cephalic) flexure - forebrain folds back under rest of the brain
Ventral folding occurs at cervical flexure between myelencephalon and spinal cord
Reverse dorsal flexion at pontine flexure
How can the brain be divided into 2 parts
Brainstem - representing cranial continuation of spinal cord (similar organisation)
Higher centres, consisting of cerebellum and forebrain (extremely specialised)
When does differentiation of neural tube cells begin
After closure of neural tube
- Proliferation of ventricular layer of neuroepithelial cells
- Neuroblasts migrate to mantle layer (grey matter)
- Extend cell processes to marginal layer (white matter)
- Glioblasts (astrocytes, oligodendrocytes)
- Ependymal cells
Development of spinal cord
Ventricular vs pial surface
What layer eventually becomes white matter
Marginal layer → WM
What does the sulcus limitans demonstrate
Difference between where structures that are motor and strutures that are sensory are located
Ventricular layer/zone becomes
Central canal in adult
Mantle layer gives rise to
Neurons - that migrate towards alar plate
What happens to cells in the basal plate
Become more differentiated and allow for anterior median fissure
Where do cells go from the ventricular zone
To the mantle layer - gives rise to the neurons - migrate away to mantle layer and some migrate upward
What is the mantle zone (GREY MATTER) organised into
Alar and basal plates - like in spinal cord
Where is the 4th ventricle located
Where does the cerebellum arise from
Dorsal aspect of rhombic lip in brainstem along the edge of the ventricular region
Dorsal rhombic lips of alar plates
When do the cells lining the tube start to differentiate
Once the neural tube closes
Development of cerebrum
Unique pattern of porliferation, migration and differentiation in cortex
neuroepithelium - like other parts of neural tube
Proliferating cells in ventricular zone (VZ) produce waves of neuroblasts
Neurons migrate out of the VZ to establish cortical layers - grey matter of cortex
What is the VZ responsible for
Site of cell division
Cells will brcome specialised - neurons to glial cells (neuroblasts/glioblasts)
What is the guidance cue for cell differentiation
Radial glia - one edge touching ventricular to pial cells
How does the cerebrum develop
What happens to cells born in the ventricular zone
They use the radial glia to migrate out along the width of the neural tube as it’s developing
How does the cerebrum develop
In cortical plate, neurons become organised into well defined layers
Neurons leave VZ and migrate past the older neurons (in deeper cortical layers) to the outermost cortex
The layering of the cortex is thus an inside-first outside-last layering
What are the disorders of neuronal migration
Defects in lamination of the 6-layered structure
Failed formation of gyri and sulci
What are mini columns
Change in mini-columns with autism
Vertical (radial) assemblies of neurons
Patients with autism shown to have an increased packing density of columns - thought to be anatomically and functionally interconnected
Glissincephaly
Smooth surface of the brain - only has a certain capacity to densely pack neurons
What gives rise to gyri
Sulci
When does myelination occur
Towards the end part of foetal development up to the age of 2
Overview of embryology
