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 cord
rostral end – brain
if neural tube fails to close
caudal – spina bifida
rostral – 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 end
1. prosencephalon – forebrain vesicle
2. mesencephalon – midbrain vesicle
3. rhombencephalon – hindbrain vesicle
when neurulation is complete – considered
an embryo!
After 3 vesicles are formed –
we see 2 flexures:
1. cervical (sc and
hindbrain)
2. cephalic (hindbrain and
midbrain)
See further specialization of neural tube
further divisions –
1. prosencephalon – forebrain vesicle
telencephalon - cortex
diencephalon – thalamus, hypothalamus
2. mesencephalon – midbrain vesicle
3. rhombencephalon – hindbrain vesicle
metencephalon- pons and cerebellum
myelencephalon - 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)
• medulla
structure
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