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Module 8 > Embryology of CNS > Flashcards

Embryology of CNS Flashcards

1
Q

what are the 3 stages of development of the neural tube

A
  1. neural plate: ectodermal cells overlaying the notochord become tall columnar (in contrast to surrounding ectorderm that produces epidermis of skin)
  2. neural groove
  3. neural tube: the dorsal margins of the neural groove merge medially, forming a neural tube composed of columnar neuroepithelial cells surrounding a neural canal
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2
Q

what does the notochord induce

A

overlaying ectoderm to become neuroectoderm and form a neural tube

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3
Q

how does closure of the neural tube progress

A

rostrally and caudally from the level of the most caudal division of brain

the caudal closure forms the majority of the spinal cord

defect of closure of neural tube are the cause of various embryological malformations

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4
Q

what are the outcomes of neural tube differentiation and the associated structures

A
  1. neural tube –> CNS (brain + spinal cord)
  2. cavity of tube (neural cavity) –> central canal of spinal cord and ventricles of brain
  3. neural crests: arise from border of neural plate and surface ectoderm –> form a column of cells dorsolateral to neural tube
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5
Q

what are the outcomes of neural crest differentiation

A
  1. neurons of PNS with their cell bodies located in spinal ganglia
  2. neurolemmocytes (Schwann cells) of PNS (myelination of nerves)
  3. ganglionic neurons of ANS and enteric nervous system
  4. others: adrenal medulla cells, melanocytes of skin, variety of structures in the face, etc.
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6
Q

what are the structures shown

A
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7
Q

what occurs to the neural tube

A

initially one cell thick

division of the cells located close to the central canal = germinal layer (start dividing and form other cells)

migration towards the periphery and differentiation of the post-mitotic cells (resulting in formation of a concentric 3 layer structure)

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8
Q

what are the two cell types in the differentiation of neural tube development

A
  1. immature neurons
  2. spongioblasts
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9
Q

what are immature neurons

A

differentiate into nmature neurons (no further division occurs)

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10
Q

what are spongioblasts

A

progenitors of the neurectodermal supporting cells of the nervous system = neuroglia (oligodendrocytes and astrocytes)

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11
Q

what are the 3 concentric layers

A
  1. mantle layers: develop into grey matter (where neuronal cell bodies are located)
  2. marginal layer: becomes white matter (where axons the neurons are located)
  3. the neural canal becomes the central canal in spinal cord and the ventricular system in the brain. lined by ependymal cells
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12
Q

what is the neural canal lined by

A

ependymal cells originating from germinal layer –> only remnant of this germinal layer = one cell thickness

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13
Q

what is the final steps of neural tube development

A
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14
Q

how does the dorsal nerve roots develop in the sensory system

A

Axons emerge from the segmental spinal ganglion (neural crest)

Form afferent neurons (sensory)

Cell body is in the spinal ganglion

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15
Q

how does development of ventral nerve roots in the motor system occur

A

Axons grow from the basal plate (ventral horn of the neural tube) out of the neural tube

Form efferent neurons:

–General somatic efferent neurons (muscles)

–General visceral efferent neurons (autonomic nervous system)

Cell body is in the spinal cord

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16
Q

how does the brain develop in the first steps

A

The rostral end of the neural tube develops rapidly into 3 vesicles then 5 vesicles

Early in its development, the prosencephalon develops lateral enlargements:

optic vesicles (will lead to the formation of the eye and optic nerves).

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17
Q

what are the structures shown here

A
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18
Q

what structures are shown here

A
19
Q

what structures are shown here

A
20
Q

what structures are shown here

A
21
Q

how is the forebrain organized

A

in the telecephalon the arrangement is different from the basic neural tube organization

22
Q

where are the neuronal cell bodies located in the forebrain organization

A

neuronal cell bodies are located in 2 locations

  1. most of grey matter is located in cerebral cortex
  2. others are located deeply in subcortical basal nuclei
23
Q

how is the white matter organized in the forebrain

A

white matter tracts (axons) are located deep inside telencephalon

24
Q

where is the commissural in the forebrain

A

between cortical areas from one hemisphere to the other

25
Q

where is the white matter association fibres

A

between cortical areas within hemispheres

26
Q

where are the white matter projection fibres

A

connecting cortical areas of a hemisphere and brainstem nuclei

27
Q

what are the white matter tracts

A
  1. commissural fibres (corpus callosum)
  2. projection fibres (internal capsule)
  3. association fibres (long and short)
28
Q

what are the structures shown

A
29
Q

what are the 3 layers of connective tissue of the meninges

A
  1. dura matter: thick, fibrous layer
  2. arachnoid: thin layer, which encloses the cerebrospinal fluid within the subarachnoid space
  3. pia matter: thin layer, adherent to the CNS parenchyma
30
Q

what are the 3 connective tissue layers derived from and what do they cover

A

derived from neural crests with a small mesodermal contribution

cover the brain and spinal cord

31
Q

what are the main type of malformations in development

A
  1. hydrocephalus
  2. neural tube defects
  3. migration disorders
  4. encephaloclastic defects (destructive lesion)
  5. others: cerebellar and spinal cord malformations
32
Q

what is anecephaly/atelencephaly

A

failure of development of telencephalic vesicles

presence of a calvarial defect = cranioschisis

brainstem and cerebellum are present –> reduced in size

CSF leakage from calvarial defect

33
Q

what is cranial bifidum (two forms)

A

defect of closure of cranium

various form depending on nature of tissue protruding through defect

meningocele: protrusion of meninges, covered by skin through cranium bifidum

meningoencephalocele: as above but also contains brain parenchyma in protrusion

34
Q

what does cranium bifidum normally effect

A

dogs at a young age –> median 6.5 months

35
Q

what are the presenting problems with carnium bifidum

A

seizures and behavioural abnormalities

36
Q

what are the causes of cranium bifidum

A
  1. genetic: craniofacial malformation
  2. teratogenic substances: griseofulvin treatment of pregnant queens
  3. folic acid deficiency: well recognized cause in people
  4. cause unknown
37
Q

what is diecephalus

A

due to incomplete duplication (partial twins)

38
Q

what is holoprosencephaly

A

holoprosencephaly: failure of cleavage in two separate telencephalic vesicles

39
Q

what is lissencephaly

A

smooth brain without gyri/sulci and pachygyria (thick cerebral cortex)

might be associated with cerebellar hypoplasia

40
Q

what is hydranencephaly

A

–Almost complete absence of cerebral cortex, reduced to a thin layer

–Frequently secondary to viral infection, leading to destruction of germinal layer (e.g. BVD or Blue tongue viruses).

–The cerebrospinal fluid fills the “gap” left by the missing cortex

41
Q

what is chiari-like malformation

A

–Common in Cavalier King Charles Spaniels and Brussels Griffon

–caudal cranial fossa that is too small for the volume of brain tissue that it contains ->

–herniation of the caudoventral cerebellar vermis into the foramen magnum in toy dogs and other small-breed dogs ->

–dilation of the central canal is hydromyelia; a cavitation of the spinal cord parenchyma is syringomyelia.

42
Q

what is spina bifida

A

–Frequent vertebral malformation due to a defect of closure of the neural tube

43
Q

what is the different degrees of severity of spina bifida

A

Can be only a defect in formation of vertebra (split vertebra) –> usually not associated with clinical signs

Can have various degree of protrusion of neuroectodermal and associated structures through the defect (e.g. meningocoele = only meninges protrude or meningomyelocoele = meninges and spinal cord or nerves protrude through the defect)

44
Q

what is dermoid sinus

A

–Incomplete separation of neural tube from surface ectoderm

–Different degree of severity depending on whether the tract reaches or not the vertebral canal

–Frequent in certain breeds (e.g. Rhodesian Ridgeback).

Module 8 (43 decks)

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