Neural Developments & Malformations I Flashcards
the neural plate forms from what tissue?
what causes the neural plate to form?
- ectoderm
- the underlying notochord & paraxial mesoderm
outline the sequence of events in neural tube formation.
when does neural tube formation begin and end?
where does neural tube formation occur?
day 20-22
in the cervical region.
steps:
- neural plate forms from ectoderm, d/t notochord & paraxial mesoderm
- neural folds - lateral elevations of the neural folds - develop
- neural tube forms from fusion of neural folds
what occurs after the neural tube has formed?
the neural tube extends cranially & caudally, and is in communication with the amniotic cavity
what are the neural tube neuropores?
when do they close?
why is this important?
- are the site of communications between the neural tube and amniotic cavity.
- they close after formation of neural tube vascularization is complete
- cranial neuropore: closes day 25
- caudal neuropore: closes day 27
what does the lumen and walls of the neural tube develop into?
- walls: the brain & spinal cord
- lumen: its innermost cavity, the neural canal, forms
- the ventricles of the brain
- the central canal of spinal cord
what is spina bidifa?
what is its cause?
how does it present?
- definition: lack of vertebral arches
- cause: a failure of the closure of the neural tube
- presentation: three main presentations that lack in severity
- spina bifida occulta
- meningocele
- meningomyelocele
in normal anatomy, how far should the meninges extend?
up until the proximal-most part of the spinal nerve, near the intervertebral foramen
in other words: not past the peduncles
spina bifida - prentation of
- spinal cord
- meninges
- other
- spinal cord - normal (or filum terminate connected to subQ)
- meninges - normal - i.e., don’t pass pedicles)
- other: hair skin patch overlies defect
meningocele - prentation of
- spinal cord
- meninges
- other
- spinal cord: normal - no extrusion of neural tissue
- meninges: extrude dorsally
- other: mild disuprtion of bladder / bosel control
meningomyelocele - presentation of
- spinal cord
- meninges
- other
- spinal cord: extruding neural tissue
- meninges: extrude dorsally + meningeal sac contains malformed cord
- other: LE dysfunction, loss of bowel & bladder control
during what part of the vertebral column are meningocele & meningomyelocele most common?
lumbosacral
what are the neural tube defects of the brain?
- craniochischisis
- encephlocele
- anencephaly
craniorachischis
- cause
- presentation
- prognosis
- cause: neural tube fails to close at the cranial spinal cord - hindbrain junction
- presentation: abormal spinal cord located outside of body, m/c occipital region
- prognosis: rarely compatible with life
encephalocele
- cause
- presentation
- prognosis
- prognosis: defect in skull (m/c occipital): allows brain to protrude through
- presentation: brain protrudes through occipital skull
- prognosis: smaller cases may be resolved surgically, many incompatible with life
anencephaly
- cause
- presentation
- prognosis
- cause: malformation at anterior end of neural tube -> disruption of forebrain development
- presentation: absence of brain/calvaria
- prognosis:stillborn -> die within a few hours
which part of the neural tube develops into the spinal cord?
the part caudal to the fourth pair of somites
the wall of the neural tube develops into what three general zones?
- from deep -> superficial (in -> out)
- ventricular
- intermediate
- marginal
what is the ventricular zone lined with?
-
neuroepithelium: psuedostratified columnar neuroepithelium, made of
- ependymal cells - ultimately line central canal
- glioblasts
- neuroblasts
what cells does the neuroepithelium give rise to?
(lining of ventricular zone of neural tube)
- ependymal cells: will line central canal
- glioblasts: differentiate into astroblasts & oligodenroblasts
- neuroblasts
glioblasts
- migrate how?
- difffereniate into what cells?
- migration: move superficially into intermediate + marginal zones
- differentiate into:
- astocytes: protoplastmic, fibrous
- oligodendrocytes: myelinate axons in the CNS
what are microglial cells?
macrophages of the CNS that migrate in from blood (are part of monocytic phagocyte system)
what are radial glial cells?
why are they important?
- they are the first cell to form in the diferentiation of glioblasts
- serve as a scaffolding on which developing neurons can migrate in -> out of neural tube
what directs & faciliates migration of developing neural cells? how?
what occurs to neurons as the migrate?
- migration directed by: neurochemical transmitters (chemo-attractants, repellents), which drive the movement of the growth cone, the tip of the developing axon immature
- migration facilitated by: radial glial cells, which serve as scaffolding
- as neurons migrate, they differentiate
what part of the neural tube wall is the destination for immature neurons?
what occurs once the neurons arrive?
- the intermediate zone (middle zone)
- once neurons arive, they:
- produce dendrites & axons that extend into the marginal zone
- form aggregations: early nuclei
what are aggregations?
groups of immature neurons in the intermediate zone of the neural tube wall (their destination).
are early forms of nuclei
what is the significance of the marginal zone?
- becomes invaded with axons & dendrites from neurons in the intermediate zone, after which synaptogenesis occurs
- gives rise to the white matter of the spinal cord
what is the significance of each neural tube wall zone?
- ventricular: site of massive neurolast mitosis
- intermediate: destination for neurons
- marginal: receives axons & dendrites from intermediate zone -> forms white matter of spinal cord
do neurons go mitosis after the ventricular zone?
no
synaptogenersis
- results in?
- is triggered by?
- is guided by?
- involves what processes?
- has what significance?
- results in: synapse formation
- triggered by: invasion of axons & dendrites into marginal zone
- guided by:
- neurotrophins: permits neuronal growth & survival
- astrocytes
- involves: significant neuronal cell death (75% of neurons that just migrated)
- significance: random pattern of cell death -> massive levels of plasticity:
- ”everyones brain is different”
what is the cause of the cell death in synaptogenesis?
insufficient neurotrophins
neurotrophils promote neuronal growth & survival, & there is not enough for all neurons that migrated
what is he sulcus limitans?
what does it form?
-
a longitudinal groove formed from the thickening lateral walls of the growing nueral tube/ divides the lateral tube into an:
- basal plate - ventrally
- alar plate - dorsally
what do they alar plate and basal plate form?
- alar plate = afferents (sensory)
- dorsal horn
- dorsal median sulcus
- basal plate = efferents (motor)
- ventral & lateral horn
- ventral median fissure
from what does the ventral median fissure form?
the basal plate of neural tube
syringomyelia
- pathogenesis
- demographics
- presentation
- pathogenesis: associated with trauma, or charli I formation
- demographics: adults
- presentation:
- a spinal cord cyst that is
- fluid filled (but NOT CSF)
- within gray matter
- not contiguous with central canal \
- m/c in cervical & upper thoracic segments
- loss of pain’temp sensations in upper extremities
- a spinal cord cyst that is
