cns development 1.a somewhat general overview of cns development
TRANSCRIPT
CNS development
1. A somewhat general overview of CNS development
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
• blastula invaginates giving rise to 3 layers – called gastrulation and the structure is now called a gastrula
• blastula invaginates giving rise to 3 layers – gastrulation
– endoderm• guts, lungs, liver, internal organs
– mesoderm• muscles, skeleton, connective tissue, cardiovascular
system, urogenital system
– ectoderm
• neural groove flattens and forms the neural plate – this folds into a tubular structure called the neural tube
The 3 dimensions of the neural tube
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
• cavity of the neural tube forms the ventricular system
During neurula stage – see further specialization of neural tube
cephalic end differentiates into 3 primary vesicles
1.
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
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!
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
corticogenesis
• - develops from inside out
Axon and dendrite development
• When does dendritic growth occur?
• Environmental influence?
Synaptogenesis
general terms
• nerves• tracts• ganglion• nucleus
myelination
• What is responsible for myelination?
• How long does myelination take?
Autonomic NS
Somatic NS
• 31 pairs of spinal nerves
label the diagram
• sensory neurons– clustured in DRG
– pseudo unipolar neurons• bifurcated axon with central and peripheral branches
components of SC
• dorsal horn – – sensory relay neurons
• ventral horn –– motor nuclei
• white matter – – longitudinal tracts of myelinated axons
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
• corticospinal tract– humans - ~ 1,000,000 axons – originate in motor cortex; pyramidal motor system– makes monosynaptic connections with motor neurons
• 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.
ways to determine region of spinal cord• relative white to gray matter• configuration of gray matter• specific nuclei- clarkes nucleus
Cranial nerves primarily serve head and face
Brain
• hindbrain, midbrain and forebrain
hindbrain
• medulla
• pons
• cerebellum
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
hindbrain
• medulla• pons• cerebellum
– roles:
midbrain
• structures:
midbrain
diencephalon (part of the forebrain)
• thalamus– role:
• hypothalamus– role:
The thalamus communicates with much of the cerebral cortex - serving as a sensory and motor information relay.
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
telencephalon
• basal ganglia
• limbic system
• cerebrum (cerebral hemispheres)
telencephalon
• cerebrum (cerebral hemispheres)– SOME TERMS: – fissures – large grooves on cerebrum surface– gyrus – outswelling observed on cerebrum– sulci – smaller grooves on cerebrum
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
telencephalon
• cerebrum (cerebral hemispheres)– 4 lobes
• primary and association cortices
– key differences in primary cortices
• What do we know about the extent of innervation as it relates to sensory information?
• Explain the statement that functional systems are hierarchically organized.
Some questions…..
• Differentiate between unimodal association areas and multimodal association areas
Prefrontal association area
• functions of prefrontal cortex
• lesions –
• tests of frontal lobe function