Development of CNS Flashcards by Fatih Koc

Germ layer giving rise to both CNS/PNS and parts of skin

ectoderm

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Germ layer primarily responsible for blood vessels, bones and muscles

mesoderm

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Germ layer which yields the inner lining of vital organs including notably the liver and pancreas

endoderm

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Structuring signaling to the neural ectoderm to differentiate and thicken in the early embryo

notochord

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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

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Cells at the edge of the neural plate being to proliferate and then unit dorsally to form…

neural tube

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Pinched areas of the neural fold above the developing neural tobe

neural crest

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Opening at either end of the developing neural tube

neuropores

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Function of the anterior neuropore (aka lamina terminalis)

Blood osmoregulation in the developing embryo

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Name of the process where cells in the midline will fuse and close off (most of) the neural tube

neurulation

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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

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Structure(s) in a developed adult where the open neural tube persists

Ventricular system in the brain and central canal of the spinal cord

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Closing of the anterior neuropore

Cerebral hemispheres develop over the area with the lateral ventricles developing from the tube remnant

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Anencephaly

Failure of the anterior portion of the neural tube to close. Characterized by lack of forebrain and most other brain structures

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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

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Failure of the posterior neuropore to close

Spina bifida

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Failure of the brain to divide into hemispheres

Holoprosencephaly

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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

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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

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Diverticulation

Process of the rostral neural tube growing and differentiating in further development

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Stages of diverticulation

3 (“primitive”) vesicle and 5 vesicle stages

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Structures present in 3 vesicle stage

prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)

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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)

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Transformations from 3 to 5 vesicle stage

Prosecncephalon becomes telencephalon and diencephalon. Rhombencephalon becomes metencephalon and myelencephalon

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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