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The development of the nervous system

  • Ectoderm gives rise to entire nervous system
  • During the 3rd week ectoderm forms the neural plate
  • A longitudinal groove is developed on the neural plate called neural groove & as neural groove deepens, either side of it is called the neural fold
  • Neural folds fuse, converting the neural groove into a neural tube
  • Neural tube has 2 openings : Anterior & Posterior neuropore 
  • Anterior(cranial) neuropore closes first & 2 days later posterior(caudal) neuropore is closed (Neural tube closure is complete in 28 days)
  • A strip of ectoderm is formed from the lateral margin of the neural plate, called neural crest 

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    • Neural crest differentiate into the cells of:

    1. Posterior root ganglia
    2. Sensory ganglia of the cranial nerves
    3. Autonomic ganglia
    4. Cells of supra renal medulla
    5. Melanocytes
    • The cephalic end of the neural tube dilates to form 3 primary brain vesicles (Forebrain, Midbrain vesicle & Hindbrain vesicle) 
    • Rest of the tube elongates to form the spinal cord

    Development of the spinal cord


    • The wall of the neural tube consists of a single layer of pesudostratified columnar epithelial cells, called matrix cells
    • Matrix cells rapidly divide & produce neuroblasts  
    • Neuroblasts migrate peripherally to form the intermediate zone; it will form the grey matter of the spinal cord 
    • Intermediate zone forms 2 thickened areas, separated by sulcus limitans
    1. Anteriorly : Basal plate (Produce motor cells of the anterior column)
    2. Posteriorly : Alar plate – Small (Produce sensory cells of the posterior column)
    • Neuroblasts will give rise to nerve fibers that grow peripherally & form a layer external to the intermediate zone, forming the marginal zone; it will form the white matter of the spinal cord 
    • Matrix cells also produce
    1. Astrocytes
    2. Oligodendrocytes
    3. Microglial cells
    4. Ependymal cells (Line the neural tube)
    • The continuous growth of basal plates on either side will form anterior median fissure
    • The continuous growth of alar plates on either side will form posterior median septum
    • The lumen of the neural tube becomes the central canal

    Development of spinal nerves

    Anterior end

    • The medial group of motor neurons will leave the anterior surface of the spinal cord as the motor outflow
    • The lateral group of neurons will leave the anterior surface of the spinal cord as the autonomic Preganglionic fibers; they form the lateral grey column (T1 – L2) – That is the sympathetic outflow
    • The 2 outflows leave the anterior surface of the spinal cord & form the Ventral root of the spinal nerves

    Posterior end

    • Neural crest cells migrate to a posterolateral position on either side of the developing spinal cord 
    • They differentiate into neuroblasts & satellite (Capsular) cells 
    • Each neuroblast develops 2 processes
    • Central process
    • Grow into the posterior part of the developing spinal cord
    • These central processes are collectively called as posterior root of the spinal nerve
    • Peripheral process
    • Grow out laterally & form the axon of sensory nerve fibers
    • Peripheral processes join the anterior root to form the spinal nerve

      Development of the spinal cord in relation to the vertebral column

      • Developing vertebral column grows faster than the spinal cord
      • At birth the coccygeal end of the cord lies at the level of the L3 vertebra
      • When a LP is performed in a small child, need to use a level below L3 up to S2 (SAS ends there)
      • As a result of the development of limb buds during the 4th month, additional sensory & motor neurons are formed (Produces cervical & lumbar enlargements of the spinal cord)
      • In adult spinal cord itself is shorter than vertebral column and it usually end at L1-2


      The development of the nervous system The development of the nervous system Reviewed by Ucfm on August 03, 2010 Rating: 5
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