Download Structure of the Nervous System

Development of the
Nervous System
Development of the CNS
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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.
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Neural plate becomes the nervous system.
Neurulation
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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.
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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.
Differentiation
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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.
Other Names for the Parts
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Telencephalon and diencephalon – forebrain.
Mesencephalon – midbrain
Rhombencephalon -- hindbrain
Ventricles
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Ventricles are open, fluid-filled spaces within
the brain.
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Ventricles correspond to the three parts and
can be used as landmarks across species.
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Cerebrospinal fluid (CSF)
Cerebral aqueduct (narrow channel) identifies
midbrain.
Ventricles are continuous and continue into
spinal cord.
Neocortex
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The terms cortex and neocortex are used
interchangeably when referring to humans.
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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.
Names for Collections of Neurons
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Gray matter – neuronal cell bodies.
Cortex – a thin sheet of neurons on the brain’s
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.
Names for Collections of Axons
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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.