Development of CNS (central nervous system)

Origin: ectoderm and neural tube

(I) Neural tubeprevious notes

(II) Neural crest Ectodermal cells on lateral edge of neural tube

Derivatives of neural crest:

  1. All dorsal root ganglia
  2. Autonomic ganglia
  3. Sensory ganglia of cranial nerves V, VII, IX, X (5, 7, 9, 10)
  4. Schwann cells
  5. Medulla of suprarenal gland (chromaffin cells)
  6. Melanoblast cells
  7. Archnoid and pia mater

(III) Spinal cordCaudal part of neural tube

  • Neural tube has a single layer of simple columnar epithelium and central canal
  • The epithelium proliferates – forms 3 layers:
  1. Ependymal layer – produces cerebrospinal fluid (CSF) 
  2. Mantle layer – grey mater
  3. Marginal layer – white mater
development of spinal cord, neural tube

A groove called sulcus limitans divides the mantle layer into:

  1. Alar plate – posterior horn, sensory cells
  2. Basal plate – anterior horn, motor cells

Growth of spinal cord:

  1.  3rd month fetal life – till end of vertebral column
  2. Birth – till L3
  3. Adult – till L1/L2

Congenital anomalies of spinal cord:

  1. Spina bifida oculta – failure of fusion of one vertebrae dorsal part
  2. Meningocele – failure of fusion of 2-3 vertebra. meninges bulge out
  3. Meningo-myelocele – spinal cord bulges out
  4. Myelocele – Neural tube failed to close, neural plate exposed
Image result for meningomyelocele vs meningocele
Image result for myelocele
congenital anomalies of spinal cord

(IV) BrainCranial end of neural tube

  • Neural tube expands to form brain swelling
  • Lumen forms ventricles
  • 2 constrictions divide brain swelling into 3 parts

(V) Cerebellum Alar lamina of metencephalon

  • Alar lamina bend medially, forming medial and lateral bulges
  • The medial bulges meet each other over the roof plate of 4th ventricle, forming vermis 
  • Lateral bulge forms cerebeller hemispheres
  • Cerebeller cortex formed by – neuroblast cells migrating from mantle layer to marginal layer
  • Dentate nucleus – neuroblasts deeply situated in mantle layer
  • Cerebeller peduncles – axons of neurons of cerebeller nuclei grow out to reach brainstem
Image result for development of cerebellum