Neuroembryology Flashcards
0
Q
Spina bifida
A
-the vertebral arches and/or spinal cord fail to form completely
-Spina bifida occulta: only the vertebral arch is defective
*skin may be covered with a tuft of hair
*May occur in up to 10% of live births
Spina bifida cystica:
-Spina bifida w/ meningocele:
*meninges protrude through vertebral arch and skin
-Spina bifida w/ meningomyelocele:
*meninges & neural tissue protrude thru vertebral arch & skin
-Rachischisis: neural folds fail to elevate or close
*forming an exposed flattened mass of neural tissue.
1
Q
Neurulation
A
- 3rd week
- ectoderm over notochord thickens forming neural plate.
- Lateral edges of neural plate elevate to form neural folds.
- The depression b/t the neural folds is the neural groove.
- The folds and the groove together comprise the neurectoderm.
- Folds approach & meet each other dorsally in the midline
- create a cylinder: the neural tube.
- Cells in apex of the neural fold meet
- separate from the neural tube to form the neural crest.
- Meeting of the neural folds occurs first in the occipital region
- proceeds cranially and caudally.
- cranial end (anterior or cranial neuropore) closes on 25th day
- Lamina terminalis: site of closure of the cranial neuropore.
- The caudal neuropore closes on about day 28.
- Rostral portion of tube enlarges to become primordial brain
- caudal portions remain narrow and become the spinal cord.
2
Q
Cranial NTDs
A
- defects in the formation of skull bones and/or brain
- Meningocele: meninges bulge through an occipital bone defect
- Meningoencephalocele: meninges & brain tissue bulge through an occipital bone defect
- Meningohydroencephalocele: meninges, brain tissue and part of the ventricular system bulge through an occipital bone defect
- Anencephaly: failure of anterior neuropore closure with most of brain and skull roof absent
3
Q
Adult structures that are derived from neural crest
A
- Neural crest cells migrate from dorsal surface of tube along well-defined pathways and give rise to:
- pigment cells
- dorsal root ganglia (primary sensory neurons) and some cranial nerve sensory ganglia
- schwann cells and satellite cells
- sympathetic and parasympathetic ganglia
- adrenal medulla chromaffin cells
- C-cells of the thyroid gland
- dentin
- facial skeleton.
4
Q
Origin of Neurons
A
- neuroepithelial cells comprise ventricular zone of neural tube
- neuroepithelial cells give rise to primitive neuroblasts.
- neuroblasts in a zone around ventricular: the mantle layer
- In mantle layer, neuroblasts differentiate into neurons
- Neurons lose ability to divide
- transition from unipolar neuroblasts to multipolar neuron.
- Neurogenesis is mostly complete by six months
- Except cerebellum: cell proliferation thru the 1st postnatal year.
- neuroblasts migrate guided by radial glial fibers.
- Migration of neurons until before birth in cerebral cortex
- up to a year after birth in the cerebellum.
- Axons sprout from developing neuroblasts
- forms layer of white matter surrounding the mantle layer
- referred to as the marginal zone.
5
Q
Origin of Glia
A
- After neuroblast production ceased, the neuroepithelial cells of the ventricular zone give rise to glioblasts
- glioblasts differentiate into the macroglia
- astrocytes and oligodendrocytes
- Microglia are thought to arise from the mononuclear cell line.
- remaining neuroepithelial cells differentiate into ependymal cells
- line the central canal and the ventricles of the brain.
- These cells will produce and circulate CSF.
6
Q
Explain why the spinal cord ends at the L1 vertebral level in adults
A
- Before 3rd embryonic month, spinal cord extends the length of the vertebral column.
- Vertebral column grows faster than the cord.
- At Birth, the cord extends to L3.
- Adult cord ends b/t the L1 and L2 b/c the vertebral column grows faster
- Cauda equina extends further down the cord.
7
Q
Differentiation of the Spinal Cord: Basal Plate
A
- The mantle layer develops dorsal and ventral thickenings,
- the alar and basal plates
- Sulcus limitans: longitudinal grove in wall of the central canal
- junction b/t alar and basal plates.
- The basal plates become the adult ventral horns.
- Basal plate derivatives associated w/ motor function.
- Includes:
- lower motor neurons whose axons innervate skeletal muscle
- preganglionic autonomic neurons.
8
Q
Differentiation of the Spinal Cord: Alar Plate
A
- The alar plates become the adult dorsal horns.
- Alar plate derivatives associated w/ sensory function.
- Includes Sensory relay neurons of the spinal cord
- receive input from 1˚ afferent sensory neurons
- project to higher brain areas).
9
Q
Development of the cerebellum
A
- Developing metencephalon
- Dorsolateral part of alar plate expands to form the rhombic lips
- rhombic lips bulge into 4th ventricle, separated by thin roof plate.
- expanding rhombic lips overgrow roof plate & meet in midline.
- Vermis: midline portion of the cerebellum,
- Develops from rhombic lip site of fusion
- Cerebellar hemispheres develop lateral to the vermis.
- Rapid growth of surface layers creates an extensive foliation.
- Rhombic lip structures- extensive connections w/ cerebellum
- inferior olive, pontine nuclei
- Cerebellar neurogenesis continues up to one year postnatally,
- DNA-blocking antiviral drugs may cause cerebellar damage
- Don’t gives these drugs to neonates
- Arnold-Chiari malformation
- Cerebellar herniation is frequent in congenital hypoplasia of the posterior cranial fossa
10
Q
3 Regions of Primordial Brain
A
- The expanded rostral portion of the neural tube forms three hollow vesicles (enlargements):
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
11
Q
Derivatives of the Diencephalon
A
- Arises from Prosencephalon
- Diencephalon has thickened lateral walls derived mostly from alar plate and a thin roof plate
- Derivatives include the:
- thalamus
- hypothalamus
- subthalamic nucleus
- epithalamus and pineal gland
- choroid plexus of the 3rd ventricle
- globus pallidus
- infundibulum and neurohypophysis
12
Q
Derivatives of Telencephalon
A
- Cerebral hemispheres: originate the telencephalic vesicles
- The cavities within these vesicles become the lateral ventricles.
- The basal, ventrolateral region gives rise to the amygdala, caudate & putamen
- become separated by axons that grow through this area to form the internal capsule
- Expanding telencephalic vesicle grows in a C-shape
- brings the temporal lobe to ventral position (covers lateral diencephalon and midbrain)
- Caudate, lateral ventricle & hippocampal/fornix system are C-shaped b/c of this growth pattern
- Cortex lateral to the lentiform nucleus is overgrown by adjacent frontal, temporal & parietal lobes
- forms the insula.
- Anterior commissure and corpus callosum appear in the region of lamina terminalis.
- The anterior commissure maintains this position
- Corpus callosum grows in anterior/dorsal/posterior sequence to give it a hook-shape in the adult.
13
Q
Derivatives of Metencephalon
A
(pons and cerebellum)
14
Q
Derivatives of Myelencephalon
A
medulla
