Development Of CNS Flashcards
What is gastrulation?
The process by which all three germ layers are created.
How do we produce the neural tube?
Gastrulation produces the notochord
Notochord induces neurolation
Induction of neural plate
Elevation of lateral edges of neural plate
The depressed mid-region is the neural groove
Neural folds gradually approach each other in the midline and fuse, producing the neural tube.
What is the notochord and what does it do?
Solid rod of cells running in the midline with important signalling role.
Notochord directs conversion of overlying ectoderm to neuroectoderm.
How long does it take / when does the neural tube close?
By day 28-32, the neural tube is completely closed.
Whole process takes 10 days.
How do neural tube defects occur?
Results from failure of neural tube to fuse or failure of the neuropores (anterior and posterior) to close.
Can occur caudally or cranially.
Cranially - anencephaly (missing part of brain)
Caudally - spina bifida
What is spina bifida?
When you have two spines as the neural tube doesn’t fuse properly caudally.
Can occur anywhere along the length, most common in lumbosacral region.
Neurological deficits occur but, it is not associated with cognitive delay.
Hydrocephalus nearly always occurs.
What other neural tube defects can occur?
Anencephaly - failure of NT to close cranially
Absence of cranial structures, including brain.
Rachischisis - Failure of neural fold elevation
Both incompatible with life
How do you diagnose and prevent NTDs?
Raised maternal a-fetoprotein (not specific but sign something is wrong)
USS
Folic acid pre-conceptually and for first trimester reduces NTDs by 70%
What embryonic structure does the spinal cord come from?
Most of the length of the neural tube gives rise to the spinal cord.
How does the corda equina develop?
At the 3rd month, the spinal cord is the same length as the vertebral column.
Thereafter, the column grows faster.
Spinal roots must elongate because they still exit at the intervertebral foramen.
This forms the cauda equine.
What is the forebrain made from?
Prosencephalon
What is the midbrain made from?
Mesencephalon
What is the hindbrain made from?
Rhombencephalon
At 5 weeks of development, five secondary brain vesicles are formed. What are they?
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
Why does the neuraxis not remain straight?
Growth and development at the cranial NT exceeds available space linearly, so it must fold up.
Cervical flexure: spinal cord - hindbrain junction.
Cephalic flexure: midbrain region
What does the ventricular system develop from and what is its role?
Develop from tubular structures of the developing CNS (lumen of the tubes is the ventricles).
In an adult, these ventricles are interconnected and filled by CSF produced by the choroid plexus cells.
The ventricular system cushions the brain and spinal cord within their bony cases.
What is hydrocephalus?
A ventricular system abnormality.
Most common in newborns suffering from spina bifida.
It is readily treatable using a shunt.
Can occur anywhere there is a blockage of the ventricular system.
What are the layers of the early neural tube, from the inside out?
Neuroepithelial layer
Intermediate (mantle) layer -neuroblasts
Marginal layer -processes
The roof and floor plates regulate dorsal and ventral patterning.
Made from the alar (sensory) plate and the basal (motor) plate.
What are neural crest cells?
Cells of the lateral border of the neuroectoderm tube.
Become displaced so enter the mesoderm and undergo epithelial to mesenchymal transition.
What cells of the nervous system are derived from neural crest cells?
Cranial nerve ganglia
Spinal (dorsal) root ganglia
Sympathetic ganglia (chain and pre-aortic)
Parasympathetic ganglia
Schwann cells
Glial cells
Leptomeninges (arachnoid and pia)
What head, neck and midline structures are derived from neural crest cells?
CT and bones of face and skull
Odontoblasts
Dermis (face and neck)
C cells of the thyroid gland
What other are derived from neural crest cells?
Conotruncal septum (heart)
Melanocytes
Adrenal medulla
What conditions can you get from abnormal neural crest migration?
Hirschsprung disease (aganglionic megacolon) -only affect one structure.
DiGeorge syndrome (thyroid deficiency, immunodeficiency secondary to thymus defect, cardiac defects, abnormal faecies) -affects multiple structures.
What are the secondary brain vesicles of the prosencephalon (forebrain) and what are their mature derivatives?
Telencephalon - cerebral hemispheres
Diencephalon - thalamus
What is the secondary brain vesicle of the mesencephalon (midbrain) and what is the mature derivative?
Mesencephalon - midbrain
What are the secondary brain vesicles of the rhombencephalon (hindbrain) and what are their mature derivatives?
Metencephalon - pons, cerebellum
Myelencephalon - medulla oblongata
