Embryology-Neural Tube Defects Flashcards
At what point in fetal development does CNS development begin?
At about 2 weeks the notochord induces differentiation of the ectoderm into the neural plate (neurectoderm)
During fetal development, the neural tube walls become the CNS and the crest cells become the PNS. How do these embryological structures form?
The neurectoderm folds into the neural tube.
Why do you mostly see anencephaly and spina bifida and not mid spinal defects in spinal cord development?
The neural tube starts closing in the middle and finishes closing at the anterior and posterior neuropores
What is the embryological origin of the structure below?
It is the point where the rostral neuropore closed. This marks the junction between the diencephalon and telencephalon.
What is the most common caudal neural tube defect?
L5 or S1 fails to form the posterior vertebral arch. This type is benign and usually presents with a tuft of hair above the vertebra.
What types of caudal neural tube defects have the characteristics seen in the image below?
Spina bifida Cystica: meningiocele (meninges) and meningiomyelocele (meninge + spinal cord)
What is the most serious but least common form of caudal neural tube defects?
Rachischisis. The neural tube fails to develop and a neural plate is really all that is left.
What are the names of these different rostral neural tube defects?
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Why do pregnant women need to make sure they have adequate folic acid intake during pregnancy?
It has been shown to greatly decrease incidence of neural tube defects
Some neural crest cells go on to become a part of the PNS and some do not. Where in the developed body do you find cells that originated in the neural crests?
Epidermis (melanocytes), DRG (pseudounipolar neurons, satellite cells, Schwann cells), Sympathetic Ganglion, Adrenal Medulla, Parasympathetic Plexus and Sympathetic Prevertebral Plexus
What is the embryological origin of the formation of cleft palate?
Failed neural crest migration. Normally they migrate to help form part of the facial skeleton.
Where are the neural stem cells located in the developing embryo?
They start in the the wall of the neural tube (Neuroepithelial cells) and replicate in the ventricular zone. These give rise to all macroglia (oligodendrocytes & astrocytes) and CNS neurons.
Where do developing CNS neurons typically first develop their processes (axon & dendrite precursors)? Where do the axons go once developed?
Once they leave the ventricular zone and move to the mantle zone. The axons then extend into the marginal zone.
What part of the CNS is the last to complete development?
Cerebellum (~1 year postpartum) The rest of the CNS is done developing by the end of the second trimester.
Once the neurons have differentiated what is the second wave of neuroepithelial differentiation?
Gliogenesis. Gliablasts are formed from the neuroepithelial cells.
Where do most motor neurons and sensory neurons develop from in the spinal cord?
The mantle zone differentiates into the Alar and Basal plates. The Alar plate will make up much of the posterior horn of the gray matter in the spinal cord (sensory) and the Basal plate will make up much of the anterior horn of the gray matter in the spinal cord (motor)
What are the 5 embryological regions of the brain?
Prosencephalon -> Telencephalon, Diencephalon. Mesencephalon. Rhombencephalon -> Metencephalon, Myelencephalon
What is special about neural tube development in the upper medulla and pons?
The alar plate opens up dorsally to form the 4th ventricle.
Where are the motor and sensory regions found in the brainstem?
Due to the opening of the alar plate during development, sensory nerve nuclei are found peripherally and motor nerve nuclei are found centrally
What gets formed as the neural tube moves into the midbrain?
It narrows to form the cerebral aqueduct. Also note that the alar plate remains dorsal and the basal plate ventral.
What structure does the cerebellum develop from?
The rhombic lip which forms from the alar plate of the metencephalon (developing pons region). The rhombic lips will eventually meet in the midline to form the vermis.
What congenital malformation is seen in the image below?
Chiari I malformation. It is a cerebellar tonsillar herniation through the foramen magnum. This happens as a result in malformation of the posterior cranial fossa bones.
How does the pituitary gland develop?
The anterior pituitary develops from surface ectoderm in the primitive oral cavity (Rathke’s pouch). The posterior pituitary develops from the diencephalon, budding off of the diencephalon. They meet up and make friends as seen below.
Where do the optic nerve and tract develop from during fetal development?
Diencephalon. A pouching out of an optic vesicle first happens, then it narrows to form the optic nerve chiasm and tract. It cups to form the retina.
How do the caudate, putamen, amygdala and hippocampus all find their place in the adult brain as they move during fetal development.
First the striatal ridge forms in the telencephalon. This is the beginning of the development of the caudate, putamen and amygdala. The amygadala drops down first, leaving a c-shaped tail. Then the cerebral cortex sends fibers in that separate the caudate from the putamen. The caudate forms a c-shaped structure with a tail in the temporal lobe. Finally, the hippocampus starts in the telencephalon, but c-shaped growth puts it into the temporal lobe with the fornix extending from it.
Why does it make sense that the anterior commissure is right next to lamina terminalis?
Lamina terminalis is where the rostral neuropore closes and makes it easy for neurons to cross over here, which is what they do at the commissures.
