Overview of Nervous System Development

Mar 13, 2025

Neuroanatomy: Development of the Nervous System

Development of the Nervous System

  • Central Nervous System: Originates from the neural plate and tube.
  • Peripheral Nervous System: Originates from neural crest cells.
  • Dura Mater: From mesoderm.
  • Pia Mater & Arachnoid: From neural crest cells.
  • Neural Crest Cells: Form sensory ganglia, remain near neural tube.
  • Somitogenesis: Formation of future spinal cord connections with somite derivatives.

Importance of Folic Acid (Vitamin B9)

  • Advised for women of reproductive age: 400-800 mcg daily.
  • Reduces neural tube defects.
  • Post-neural tube defect: 4000 mcg daily recommended.

Neural Tube Formation

  • Distal portion: Forms by secondary neurulation from the tail bud.

Neural Tube and Spine Defects

  • Dysraphisms: Incomplete fusion of neural tube.
    • Types:
      • Craniorachischisis: Complete dysraphism.
      • Cranioschisis/Anencephaly: Open in cephalic region.
      • Myeloschisis: Dysraphism at spinal cord level.

Spina Bifida

  • Most likely to survive when born with spina bifida.
  • Types:
    • Occulta: Hair growth over affected region.
    • Aperta: Visible at observation.
    • Cystica: Associated with meningocele, meningomyelocele, or myeloschisis.
  • Risk Factors: Folate deficiency, Valproic Acid, diabetes, obesity, hyperthermia.

Cranium Bifidum

  • Defects in skull ossification lead to encephaloceles or cranium bifidum.

Midline Defects

  • Eye Field: Development of eye vesicles and hemispheres.
  • Sonic Hedgehog Gene: Non-expression leads to defects like holoprosencephaly and cyclopia.

Histogenesis of the Neural Tube

  • Neuroepithelial Cells: Mitotically active, forming neurons and glia.
  • Interkinetic Nuclear Migration: Nucleus moves between ventricular and pial sides for division.

Spinal Cord Development

  • Ventricular, Mantle, and Marginal Layers: Formation of zones in neural tube.
  • Spina Bifida: Lack of fusion in vertebral arches.

Neural Circuit Differentiation

  • Neuron and glial production before birth.
  • Post-birth: Dendritic arborization and synapse formation.

Reflexes

  • Babinski Reflex: Normal in infants up to 2 years.
  • Other Reflexes: Palmar, moro, asymmetric tonic neck, parachute, balance test.

Neural Crest Derivatives

  • Divided into cranial and trunk portions.
  • Cranial Neural Crest: Forms pharyngeal arches, neurocranium bones, etc.
  • Trunk Neural Crest: Forms melanocytes, Schwann cells, adrenal chromaffin cells, etc.

Neurocristopathies

  • Result from abnormal neural crest cell development.
  • Examples: Neurofibromatosis, medullary carcinoma, CHARGE association.

Spinal Cord Development

  • Alar and Basal Plates: Form sensory and motor regions, respectively.
  • Morphogens: Shh from notochord and BMPs from epidermis determine dorsal-ventral cell fates.

Development of the Brain

  • Flexures: Cephalic and cervical during the fourth week.
  • Ventricular System: Formation of lateral, third, and fourth ventricles.
  • Choroid Plexuses: Produce cerebrospinal fluid in the ventricles.

Brainstem and Cerebellum

  • Brainstem: Derives from myelencephalon, metencephalon, and mesencephalon.
  • Cerebellum: From alar plate of metencephalic vesicle, involved in balance and coordination.

Development of the Telencephalon and Diencephalon

  • Telencephalon: Formation of cerebral hemispheres, limbic system components.
  • Diencephalon: Forms thalamic structures, epithalamus, hypothalamus.

Hydrocephalus and Other Conditions

  • Hydrocephalus: Accumulation of CSF due to blocked ventricular communication.
  • Dandy-Walker Syndrome: Malformation of posterior cranial fossa.

These notes provide a comprehensive summary of the lecture on the development of the nervous system, highlighting important structures, processes, and associated conditions.