Physiological and pathological formation of the brain and spinal cord Flashcards
What happens in week 3 of embryo?
Gastrulation
Ectoderm - skin, nervous system
Endoderm - epithelial lining of gut and respiratory system, liver and pancreas
Mesoderm - notochord, muscular system
Ectoderm thickens in midline to form what?
neural plate
What do signals from notochord cause
Inward folding of ectoderm at the neural plate
What fuses and disconnects to form an autonomous neural tube?
ends of the neural plates
Where does the presumptive neural crest cells lie?
Lateral to the neural groove
What types of cells do the ectoderm turn into?
Melanocytes, Schwann cells and neurons
What types of cells do the mesoderm cells turn into?
Osteoblasts, adipocytes and chondrocytes
What do neural crest cells make?
Sensory dorsal root ganglia of spinal cord and V/ VII / IX / X
Schwann cells
Adrenal medulla
Bony skull
Meninges
When does the neural tube usually close?
End of 4th week
What causes anencephaly?
Failure to close cephalic region
What causes spina bifida?
Failure to close spinal region
Environmental factors may contribute - lack of folic acid, maternal diabetes.
What is meningocele?
Protrusion of the meninges, may or may not be skin covering it.
What is Myelomeningocele?
Protrusion and opened spinal cord
When are these neural tube defects normally known due to antenatal scanning?
By 13-14 weeks gestration
What could cause weakness of lower limbs?
L2-L4 lesion of spinal cord
Probably a mixed upper and lower motor defect
Brain at 4 weeks
Prosencephalon - gives rise to cerebral hemispheres and thalamic structures
Mesencephalon - midbrain
Rhombencephalon - medulla, pons and cerebellum
Brain at 6 weeks
Regions divides into more regions. Positions change.
Rhombencephalon will give rise to 4th ventricle, medulla, pons and cerebellum
What is hypoplasia?
Underdevelopment of parts of brain
How many layers are there in the cerebral cortex?
6
Proliferation of stem cells and migration to right positions. Controlled by many different genes.
When this doesn’t go as it should, results in intellectual disabilities.
Stem cells produce neurons. Neurogenesis.
What is microcephaly and macrocephaly mean?
Top/bottom 2.5% size of head circumference.
Microcephaly - reduced head size.
Could be caused by: Down’s Syndrome, toxic exposures during pregnancy
Macrocephaly - increased head size
What is periventricular nodular heterotopia?
Abnormal migration of neurons.
On MRI shows as nodules.
Can result in seizures, learning issues, weak arm.
Cerebrospinal fluid
Cushions brain and helps circulate metabolites
Around 120 mls
Filtrate of blood, produced as filtrate of blood at choroid plexuses in ventricles.
Absorbed via arachnoid granulations in superior sagittal sinus.
What happens if block in intraventricular canal?
In child, head expands as fissures not cemented. Macrocephaly. So always scan child with increasing head size.
In adult, brain = squished –> die.
What is hydrocephalus?
Accumulation of CSF with increased intracranial pressure
