Development of CNS Flashcards
Germ layer giving rise to both CNS/PNS and parts of skin
ectoderm
Germ layer primarily responsible for blood vessels, bones and muscles
mesoderm
Germ layer which yields the inner lining of vital organs including notably the liver and pancreas
endoderm
Structuring signaling to the neural ectoderm to differentiate and thicken in the early embryo
notochord
The neural ectoderm is signalled by the notochord to differentiate and thicken along the future midline of the back. What is formed here?
neural plate
Cells at the edge of the neural plate being to proliferate and then unit dorsally to form…
neural tube
Pinched areas of the neural fold above the developing neural tobe
neural crest
Opening at either end of the developing neural tube
neuropores
Function of the anterior neuropore (aka lamina terminalis)
Blood osmoregulation in the developing embryo
Name of the process where cells in the midline will fuse and close off (most of) the neural tube
neurulation
Three regions of the neural tube do not fuse together via neurulation and must close by other means
1) anterior neuropore
2) posterior neuropore
3) rhomboid fossa
Structure(s) in a developed adult where the open neural tube persists
Ventricular system in the brain and central canal of the spinal cord
Closing of the anterior neuropore
Cerebral hemispheres develop over the area with the lateral ventricles developing from the tube remnant
Anencephaly
Failure of the anterior portion of the neural tube to close. Characterized by lack of forebrain and most other brain structures
Small opening on the dorsal aspect of the neural tube (1/3 down its length) is referred to as the ____ _____. Cerebellum will develop over this area to close it off and form the fourth ventricle.
rhomboid fossa
Failure of the posterior neuropore to close
Spina bifida
Failure of the brain to divide into hemispheres
Holoprosencephaly
Defects in Sonic Hedgehog (Shh) signaling pathway can lead to ____ _____ or ____ _____ in mild forms while it leads to _____ in severe forms
cleft lip; cleft palate; cyclopia
Most common type of cancer in infants/children. Cells derived from neural cells of the medullary zone of the adrenals after differentiating from neural crest
neuroblastoma
Diverticulation
Process of the rostral neural tube growing and differentiating in further development
Stages of diverticulation
3 (“primitive”) vesicle and 5 vesicle stages
Structures present in 3 vesicle stage
prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
Structures present in 5 vesicle stage
1) Telencephalon (cerebral hemispheres)
2) Diencephalon (numerous structures incl. thalamus)
3) mesencephalon (midbrain)
4) metencephalon (pons and cerebellum)
5) myelencephalon (medulla)
Transformations from 3 to 5 vesicle stage
Prosecncephalon becomes telencephalon and diencephalon. Rhombencephalon becomes metencephalon and myelencephalon
cephalic flexure
the bend in the developing midbrain of the embryo used to define neuroanatomical section planes
Cavities in the vesicles in development give rise to the ventricular system. From what structure is the cerebral aqueduct derived?
mesencephalon
The caudal/posterior portion of the neural tube goes on to become the spinal cord. What are its layers (in order of formation)?
1) ventricular layer
2) marginal layer
3) mantle layer
Layer in the developing spinal cord that generates neuroblasts and glioblasts
Ventricular layer
Neuroblasts in the ventricular layer of the spinal cord differentiate into…
neurons
Glioblasts in the ventricular layer of the spinal cord differentiate into…
1) ependymal cells
2) neuroglia – including astrocytes and oligodendrocytes
Neurocyte
an immature neuron
Layer in the developing spinal cord which is comprised of the primary neuronal cell bodies that form the gray matter of the CNS
mantle layer
What forms the white matter of the CNS in the developing spinal cord?
Axons from the mantle layer soma extending into the marginal layer
Sulcus limitans
Divides neurocyte migration from the ventricular to mantle layer (spinal cord) dorsally/ventrally
Dorsally migrating neurocytes from the ventricular to mantle layer, which represent the sensory neurons of the spinal cord, form this structure
alar plate
Ventrally migrating neurocytes from the ventricular to mantle layer, which represent motor neurons of the spinal cord, form this structure
basal plate
The alar and basal plate form which structures, respectively, in the mature spinal cord
Dorsal horns (sensory) and ventral horns (motor)
Proper ending of the spinal cord
conus medullaris
Bundle of nerves which extend down from the conus medullaris at the end of the spinal cord
cauda equina
Anchors the spinal cord to the dura mater and coccyx
filum terminale
Spinal cord is stuck to the spinal canal during development. Condition may present with weakness and sensory deficits in the lower extremities that may be alleviated by transection
Tethered Spinal Cord
Pyramids of the caudal medulla contain the developing…
corticospinal tract
The alar plate gives rise to this in the developing medulla
Dorsal Column Nuclei containing neurons of the dorsal column-medial lemniscus pathway
Gracile nucleus in the medulla is used in fine touch / proprioception for what part of the body
lower body
Cuneate nucleus in the medulla is used in fine touch / proprioception for what part of the body
upper body
Function of the dorsal column-medial lemniscus pathway
sensory for fine touch and proprioception
Derived from the alar plate, this medulla structure contains relay nuclei for the cerebellum
inferior olivary nucleus
The caudal roof of the fourth ventricle is the roof plate, which contains this monolayer of ependymal cells covered with pia mater
tela choroidea
Structure which combines with invaginations of the roof plate to form the choroid plexus, which produces CSF.
Pial vessels
In the rostral medulla, motor tracts are generally found ______ while sensory tracts are found _____
medially (m=motor); laterally (side=s=sensory)
The pons carries numerous fiber tracts that convey signals in between the ____ and the _____ and/or ____ _____
cortex
brainstem; spinal cord
Two main divisions of the pons
tegmentum (dorsal pons) and the basilar pons (ventral pons)
Made up of transverse axons in the basilar pons that extend beyond the body of the pons to reach the cerebellum
middle cerebellar peduncle
What is the cerebellum derived from in development?
Rhombic lips (part of dorsal alar plate I guess?)
Primary neuronal cells of the cerebellum
purkinje cells
Layers that sensory neuroblasts of the midbrain’s alar plate gives rise to
Superior colliculus (visual) and inferior colliculus (auditory)
Form the red nucleus and substantia nigra
Basal plate of the developing midbrain
Location of the cerebral peduncle
midbrain
Anterior portion of the cerebral peduncle, which contains motor tracts from the cortex to the pons/spinal cord
crus cerebri
Motor tracts coming from the cortex contained in the crus cerebri (3)
Corticobulbar, corticospinal, corticopontine
Differentiation of the diencephalon leads to the following structures
1) thalamus
2) hypothalamus
3) epithalamus
4) subthalamus
5) optic vesicles, cups, and stalks
6) pituitary gland
Sensory relay center of the brain
thalamus
Controls autonomic function through hormones (via the pituitary gland)
Hypothalamus
Regulates olfaction, sleep/wake cycles, also includes the pineal gland
epithalamus
Site of melatonin secretion
pineal gland
Structure derived from the diencephalon which is interconnected with the basal ganglia and involved in motor control
subthalamus
Origin of the retina, optic nerve, optic chiasm and optic tract
Come from the optic vesicles, cups, and stalks which are from diencephalic vesicle walls
The anterior lobe of this structure develops from Rathke’s pouch (from ectoderm of primitive oral cavity) and posterior lobe from ventral evagination of the hypothalamus
pituitary gland (aka hypophysis)
Name of tumor from remnants of Rathke’s pouch which compresses optic chiasm and hypothalamus as the most common cause of hypopituitarism in children
craniopharyngioma
Structure from which the cerebral cortex is derived
telencephalon
Neurocytes migrating from the mantle to marginal layer of the developing telencephalon form…
Neocortex and allocortex (includes paleocortex [olfactory] and archicortex [hippocampus])
Left and right hemispheres of the cerebral cortex are connected by…
Commissures, which are fiber bundles that connect via the lamina terminalis
Commissures linking hemispheres of the brain
1) anterior commissure (connects temporal lobes, olfactory cortices, and olfactory bulbs)
2) posterior commissure (connects pretectal structures)
3) corpus callosum (connects homotypical regions on both sides of the brain)
Origin of the corpus striatum
Derived from the telencephalon
Five structures of the corpus striatum
1) caudate nucleus
2) putamen
3) amygdaloid nucleus
4) claustrum
5) globus pallidus
The putamen and globus pallidus together make up the…
lentiform nucleus
Separates the lentiform nucleus and caudate nucleus
internal capsule
The caudate nucleus, putamen, and global pallidus together with the substantia nigra collectively make up the…
basal ganglia
Effect of zika virus
Microcephaly/microencephaly (small head/brain)
Zika virus infects neural stem cells and reduces their numbers in this stage of development
first critical period
Period of development characterized by neuron process (presynaptic axons and postsynaptic dendrites) growth and the formation of synaptic connections from the trimester to around 2 years of age
second critical period
These cells stimulate the activity of the second critical period by secreting instructive signals that facilitate the formation of synapses between appropriate axons/dendrite pairs.
astrocytes
What occurs in the third stage of neuronal network development (not necessarily a critical period but continuous with them)?
Myelination
Fourth stage of neural network development
synaptic refinement by astrocytes and microglia
Lissencephalic appearance
Smooth brain. Used in the context of no gyri/sulci present in a four month brain.
Matured gyri/sulci observed in the brain
gyrencephalic
Least severe form of the posterior neuropore failing to close properly
spina bifida occulta
Most common spina bifida variation in which parts of cerebellum and medulla are pulled through the foramen magnum, extending into the spina canal. Results in neck pain, unsteady gait, difficult swallowing, and coordination problems.
Meningomyelocele. Typically present in Arnold-Chairi malformation.
Besides meningomyelocele, this condition also associated with Arnold-Chiari malformations features spinal cord cysts which induce bilateral loss of pain and temperature in upper extremities
Syringomyelia
Myeloschisis
most severe spina bifida variant, where the extruded nervous tissue is not covered by skin/meninges
Failure in ossification in which the skull fails to close/ossify. May result in hydrocephalus, limb paralysis, and ataxia.
encephalocele
Hydrocephalus
Excess CSF (from blockage of circulation or overproduction) leads to dilation of any or all of the ventricles
Lack of muscle coordination/control
ataxia
A type of occipital meningocele where a posterior fossa cyst leads to dilation of the fourth ventricle
Dandy-Walker Syndrome
Results of Dandy-Walker Syndrome
- Elevated confluence of sinuses
* Agenesis (improper formation) of the cerebellar vermis and splenium of corpus callosum
Symptoms of hydrocephalus
Headaches, vomiting, irritability, seizures, poor muscle tone, and deficient growth
Agenesis of corpus callosum
Improper connectivity between the hemispheres, regulated by a specific class of astrocytes
Agyria
condition of lissencephaly (smooth brained)
Polymicrogyria
Excessive, small, poorly-formed gyri
Heterotopia
Improper neuron localization
These abnormalities occur as a result of loss of brain tissue (necrosis), often due to hypoxic/ischemic events like fetal stroke.
encephaloclastic defects
Porencephaly
A loss of tissue leading to abnormal opening from the ventricular system to the brain surface
Hydranencephaly
Necrosed brain tissue is replaced with fluid enclosed in a thin membrane
