Development of the Nervous System

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Development of the Nervous System
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Development of the CNS

• The embryo begins as a flat disk with three
  layers of cells.
• Endoderm forms the lining of the viscera
  (internal organs).
• Mesoderm becomes the bones and muscles.
• Ectoderm gives rise to the nervous system and
  skin.
• Neural plate becomes the nervous system.

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Neurulation

• At about 3 weeks, a rostral to caudal groove
  forms in the neural plate.
• The two sides of this groove fold together and
  fuse forming a neural tube.
• The entire nervous system develops from the
  neural tube.
• Part of the tube pinches off and becomes the
  neural crest the neurons of the peripheral
  nervous system.

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Differentiation

• Structures become more elaborate and specialized
  during development.
• The neural tube forms three vesicles.
• Forebrain becomes the neocortex.
• Midbrain becomes the tegmentum and tectum
  (substantia nigra, inferior/superior colliculi)
• Hindbrain becomes the cerebellum, pons, medulla,
  and brain stem.

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Other Names for the Parts

• Telencephalon and diencephalon forebrain.
• Mesencephalon midbrain
• Rhombencephalon -- hindbrain

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Ventricles

• Ventricles are open, fluid-filled spaces within
  the brain.
• Cerebrospinal fluid (CSF)
• Ventricles correspond to the three parts and can
  be used as landmarks across species.
• Cerebral aqueduct (narrow channel) identifies
  midbrain.
• Ventricles are continuous and continue into
  spinal cord.

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Neocortex

• The terms cortex and neocortex are used
  interchangeably when referring to humans.
• Only mammals have neocortex.
• Neocortex is used for different things in
  different species.
• Evolution has its greatest impact on the size and
  function of the neocortex.
• Localization of functions to areas of the brain
  is referenced to Brodmann areas.

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Names for Collections of Neurons

• Gray matter neuronal cell bodies.
• Cortex a thin sheet of neurons on the brains
  surface.
• Nucleus a mass of neurons deep in brain.
• Substantia related neurons with less distinct
  borders than a nucleus.
• Locus small, well-defined group of cells.
• Ganglion group of peripheral NS neurons.

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Names for Collections of Axons

• Nerve bundle of axons in peripheral NS.
• White matter CNS axons.
• Tract axons with a common origin and
  destination.
• Bundle axons that run together for awhile.
• Capsule axons connecting brain stem with
  cortex.
• Commisure axons connecting hemispheres.
• Lemniscus a tract that runs through the brain
  like a ribbon.