CNS development 1.A somewhat general overview of CNS development.
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Transcript of CNS development 1.A somewhat general overview of CNS development.
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CNS development
1. A somewhat general overview of CNS development
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In the beginning……
• zygote – fertilized egg; – undergoes a number of divisions with overall size
unchanged and divisions resulting in smaller and smaller cells (cleavage) to form the BLASTULA
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• blastula invaginates giving rise to 3 layers – called gastrulation and the structure is now called a gastrula
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• blastula invaginates giving rise to 3 layers – gastrulation
– endoderm• guts, lungs, liver, internal organs
– mesoderm• muscles, skeleton, connective tissue, cardiovascular
system, urogenital system
– ectoderm
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• neural groove flattens and forms the neural plate – this folds into a tubular structure called the neural tube
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The 3 dimensions of the neural tube
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longitudinal –
caudal end – spinal cordcaudal end – spinal cordrostral end – brainrostral end – brain
if neural tube fails to closeif neural tube fails to closecaudal – spina bifidacaudal – spina bifidarostral – anencephalyrostral – anencephaly
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• cavity of the neural tube forms the ventricular system
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During neurula stage – see further specialization of neural tube
cephalic end differentiates into 3 primary vesicles
1.
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During neurula stage – see further specialization of neural tube
3 swellings at rostral end1. prosencephalon – forebrain vesicle
2. mesencephalon – midbrain vesicle
3. rhombencephalon – hindbrain vesicle
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After 3 vesicles are formed – we see 2 flexures:
1. cervical (sc and hindbrain)
2. cephalic (hindbrain and midbrain)
when neurulation is complete – when neurulation is complete – considered an embryo!considered an embryo!
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See further specialization of neural tube
further divisions – 1. prosencephalon – forebrain vesicle
telencephalon - cortexdiencephalon – thalamus, hypothalamus
2. mesencephalon – midbrain vesicle
3. rhombencephalon – hindbrain vesiclemetencephalon- pons and cerebellummyelencephalon - medulla
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corticogenesis
• - develops from inside out
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Axon and dendrite development
• When does dendritic growth occur?
• Environmental influence?
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Synaptogenesis
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general terms
• nerves• tracts• ganglion• nucleus
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myelination
• What is responsible for myelination?
• How long does myelination take?
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Autonomic NS
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Somatic NS
• 31 pairs of spinal nerves
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label the diagram
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• sensory neurons– clustured in DRG
– pseudo unipolar neurons• bifurcated axon with central and peripheral branches
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components of SC
• dorsal horn – – sensory relay neurons
• ventral horn –– motor nuclei
• white matter – – longitudinal tracts of myelinated axons
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components of SC (con’t)
• white matter –– dorsal columns
• contains ascending axons carrying somatosensory info
– lateral columns• both ascending axons and descending axons
– ventral columns• ascending somatosensory and descending axons
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• corticospinal tract– humans - ~ 1,000,000 axons – originate in motor cortex; pyramidal motor system– makes monosynaptic connections with motor neurons
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• The corticospinal tract mostly contains motor axons.
• The rubrospinal tract – 2ndairy motor system - responsible for large muscle movement such as the arms and the legs (flexor and extension, muscle tone).
• The spinothalamic tract is a sensory pathway originating in the spinal cord that transmits information about pain, temperature, itch, some measures of touch to thalamus.
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ways to determine region of spinal cord• relative white to gray matter• configuration of gray matter• specific nuclei- clarkes nucleus
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Cranial nerves primarily serve head and face
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Brain
• hindbrain, midbrain and forebrain
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hindbrain
• medulla
• pons
• cerebellum
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hindbrain (con’t)
• medullastructure
resembles SC
contains:early relay nuclei in taste, hearing, maintenance of
balance, neck and facial muscles
• pons– ventral portion – pontine nucleus – info about movement and
sensation from cc to cerebellum– dorsal portion – respiration, taste, sleep
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hindbrain
• medulla• pons• cerebellum
– roles:
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midbrain
• structures:
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midbrain
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diencephalon (part of the forebrain)
• thalamus– role:
• hypothalamus– role:
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The thalamus communicates with much of the cerebral cortex - serving as a sensory and motor information relay.
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components of the thalamus
• nuclei– relay or diffuse projections- classified based on location
• internal capsule– large bundle of fibers carrying most of axons
running to and from cerebral hemispheres• massa intermedia
– connects left and right thalamus
• reticular nucleus– role – feedback to output nuclei of thalamus - GABA
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telencephalon
• basal ganglia
• limbic system
• cerebrum (cerebral hemispheres)
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telencephalon
• cerebrum (cerebral hemispheres)– SOME TERMS: – fissures – large grooves on cerebrum surface– gyrus – outswelling observed on cerebrum– sulci – smaller grooves on cerebrum
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cerebral cortex layers
• distinctive laminar structure of certain cortices provides information regarding region of cortex
– ex. Layer IV – main target of sensory info from thalamus
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telencephalon
• cerebrum (cerebral hemispheres)– 4 lobes
• primary and association cortices
– key differences in primary cortices
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• What do we know about the extent of innervation as it relates to sensory information?
• Explain the statement that functional systems are hierarchically organized.
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Some questions…..
• Differentiate between unimodal association areas and multimodal association areas
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Prefrontal association area
• functions of prefrontal cortex
• lesions –
• tests of frontal lobe function