Embryology Flashcards
Briefly describe the formation of the neural tube
Gastrulation produces the notochord which secretes signalling molecules that cause neurulation
There is then induction of the neural plate with elevation of the lateral edges of the neural plate
Neural folds gradually approach each other and fuse in the midline to produce the neural tube
How does the neural tube fuse along its length and what are found at the ends of the neural tube
The neural tube fuses from the middle first and then moves cranially and caudally
Cranial/anterior neuropore found cranially which fuses first
Caudal/posterior neurpore found caudally which fuses last
Describe the formation of the ventricular system
Lumen of the neural tube persists and forms the ventricular system with each primary brain vesicle forming one part of the system
Describe the development of the cranial portion of the brain
Cranial portion of the neural tube has 3 dilatations that form 5 dilatations which then go on to form the parts of the brain
During neural fold formation, 3 primary brain regions can be distinguished
Once neural tube closes the dilatations become the primary brain vesicles which then go on to form the 5 primary brain vesicles
What are the 3 primary brain vesicles and what do they go on to form
Forebrain - prosencephalon -> telencephalon and diencephalon
Midbrain - mesencephalon -> mesencephalon
Hindbrain - rhombencephalon -> metencephalon and myelencephalon
What are the 5 primary brain vesicles and what parts of the brain do they form
Telenecephalon -> cerebral hemispheres
Diencephalon -> thalamus
Mesencephalon - midbrain
Metencephalon -> pons and cerebellum
Myelencephalon -> medulla oblongata
Describe the development of the spinal cord
Most of the neural tube forms the spinal cord
The vertebral column grows faster than the spinal cord so the spinal roots must elongate to exit at their intervertebral foramen forming the cauda equina
Why does the neural tube have to bend during development and what are the two parts where it bends called
Neural tube has to bend to allow the brain to fit into a small space as the growth and development at the cranial end exceeds the available space so it must fold to fit
Cervical flexure - spinal cord and hindbrain
Cephalic flexure - midbrain region
Describe the organisation of the neural tube
The inside layer of the NT is a neuroepithelial layer that secretes CSF
The intermediate/mantal layer contains neuroblasts and is split into alar and basal plates
There is a roof plate at the dorsal aspect and a floor plate at the ventral aspect
There is an outer marginal layer that contains processes from the developing neuroblasts
What do the alar and basal plates go on to form and what drives their development
Alar plate is stimulated by the roof plate to become sensory
Basal plate is stimulated by the floor plate to become motor
What are the neural crest cells and what do they do
Neural crest cells are a group of cells found on the lateral border of the neuroectoderm tube that become displaced and enter the mesoderm as the neural tube folds
They undergo epithelial to mesenchymal transistion and help to form neuronal type tissue
What conditions can arise from neural tube defects
Anecephaly
Spina bifida - meningocele and myelomeningocele
Rachischisis
What is anacephaly
Anacephaly is where there is failure of the NT to close cranially resulting in absence of cranial structures
What is spina bifida, where does it most commonly occur and what are the two types
Spina bifida is where there is a caudal neural tube defect
Most commonly occurs in the lumbosacral region
Meningocele - where only CSF and meninges form a cyst due to a defect in the vertebral body
Myelomeningocele - where there is a defect in the vertebral body with part of the spinal cord herniating out along with CSF and meninges
What is rachischisis
Rachischisis is where there is failure of neural fold elevation resulting in no neural tube formation so no CNS formation
