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13# Development of the CNS
1. The central nervous system primarily originates from which embryonic germ layer?
Mesoderm
Ectoderm
Endoderm
Neural crest
Explanation:
The CNS develops from the ectoderm via formation of the neural plate and neural tube.
2. Microglia are derived embryologically from:
Neural crest cells
Neuroepithelial cells
Mesoderm (mesenchymal cells)
Ectoderm
Explanation:
Microglia originate from mesoderm and function as mononuclear phagocytes.
3. The neural plate begins to differentiate under the influence of which structure?
Notochord
Somites
Primitive streak
Endoderm
Explanation:
The notochord induces overlying ectoderm to form the neural plate around the 4th week.
4. Primary neurulation begins at approximately:
Day 14
Day 18
Day 20
Day 22–23
Explanation:
Primary neurulation begins in the 4th week (22–23 days).
5. Neural tube closure occurs first in which region?
Cranial region
Cervical region
Caudal region
Lumbar region
Explanation:
Fusion starts in the cervical region and proceeds cranially and caudally.
6. The rostral neuropore normally closes on which day?
Day 25
Day 22
Day 27
Day 30
Explanation:
The rostral neuropore closes around day 25 of development.
7. Failure of closure of the rostral neuropore results in:
Spina bifida
Hydrocephalus
Anencephaly
Microcephaly
Explanation:
Failure of rostral neuropore closure leads to anencephaly.
8. Neural crest cells give rise to all of the following EXCEPT:
Dorsal root ganglia
Schwann cells
Adrenal medulla
Oligodendrocytes
Explanation:
Oligodendrocytes arise from neuroepithelial cells, not neural crest cells.
9. The telencephalon develops into which structure?
Thalamus
Cerebral hemispheres
Midbrain
Medulla oblongata
Explanation:
The telencephalon gives rise to the cerebral hemispheres.
10. The cerebellum develops from which secondary vesicle?
Myelencephalon
Diencephalon
Metencephalon
Mesencephalon
Explanation:
The metencephalon forms the cerebellum and pons.
11. Secondary brain vesicles appear at which gestational week?
5th week
4th week
6th week
8th week
Explanation:
Secondary vesicles form during the 5th week of gestation.
12. At birth, the spinal cord typically ends at which vertebral level?
L1
L3
S1
L5
Explanation:
At birth, the spinal cord ends around the L3 vertebral level.
13. The cauda equina is formed due to:
Overgrowth of the spinal cord
Failure of neurulation
Early cord regression
Differential growth between vertebral column and spinal cord
Explanation:
Faster growth of the vertebral column causes elongation of nerve roots forming the cauda equina.
14. Which cells myelinate axons in the CNS?
Oligodendrocytes
Schwann cells
Astrocytes
Microglia
Explanation:
Oligodendrocytes myelinate axons in the CNS.
15. Which roots become myelinated first during development?
Sensory roots
Posterior roots
Motor roots
Autonomic roots
Explanation:
Motor roots myelinate before sensory roots.
16. The leptomeninges are derived from:
Mesoderm only
Neural crest cells
Ectoderm
Neuroepithelium
Explanation:
Arachnoid and pia mater (leptomeninges) arise from neural crest cells.
17. Hydrocephalus due to aqueductal stenosis causes dilation of:
Fourth ventricle only
All ventricles equally
Only lateral ventricles
Ventricles proximal to the obstruction
Explanation:
Ventricles proximal to the obstruction (lateral and third) become dilated.
18. The major skull bone affected in infantile hydrocephalus is:
Frontal bone
Parietal bone
Occipital bone
Temporal bone
Explanation:
The frontal bone is most affected due to increased intracranial pressure.
19. Microcephaly is characterized by:
Large skull with normal brain
Normal skull with enlarged brain
Small calvaria with normal facial size
Failure of neural tube closure
Explanation:
Microcephaly presents with small calvaria but relatively normal facial size.
20. Once neuroepithelial cells differentiate into neurons, they:
Can regenerate under stress
Cannot regenerate further
Differentiate into glial cells
Become neural crest cells
Explanation:
Differentiation into neurons is a terminal stage with no further regeneration.