Origin: ectoderm and neural tube

(I) Neural tube – previous 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

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(III) Spinal cord – Caudal 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

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

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(IV) Brain – Cranial end of neural tube

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

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(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