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Flashcards in neural embryology Deck (76):
1

neural development - process

notochord induces overlying ectoderm to differentiate neuroectoderm and form neural plate ---> Neural plate give rise to neural tube and neural crest cells / notochord becomes nucleous pulposus of intervertebral disc in adults

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neural development - notochord induces

overlying ectoderm to differentiate neuroectoderm and form neural plate

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Neural plate give rise to

neural tube and neural crest cells

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neural development - parts of neural tube

alar plate (dorsal): sensory
basal plate (ventral): motor
SAME ORIENTATION AS SPINAL CORD

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from notochord to neural tube - time

day 18-day 21

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.... give rise to neural tube and neural crest cells

Neural plate

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regional specifications of developing brain - at the beginning - vesicles (number) (cavities)

3 (three primary vesicles)

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regional specifications of developing brain - three primary vesicles - parts (Walls)

1. forebrain (prosencephalon)
2. Midbrain (mesencephalon)
3. Hindbrain (rhomboencephalon)

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regional specifications of developing brain - five primary vesicles - parts (arises from)

1. Telencephalon (forebrain)
2. Diencephalon (forebrain)
3. Mesencephalon (Midbrain)
4. Metencephalon (Hindbrain)
5. Myelencephalon (Hindbrain)

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regional specifications of developing brain - forebrain (prosencephalon) gives rise to

1. Telencephalon
2. Diencephalon

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regional specifications of developing brain - Midbrain (mesencephalon) gives rise to

Mesencephalon

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regional specifications of developing brain - Hindbrain (rhomboencephalon) gives rise to

1. Metencephalon
2. Myelencephalon

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telencephalon - adults derivatives (wall and cavity)

wall: cerebral hemisphere
cavity: lateral ventricles

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diencephalon - adults derivatives (wall and cavity)

wall: thalamus + hypothalamus
cavity: third ventricle

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mesencephalon - adults derivatives (wall and cavity)

wall: midbrain
cavity: aqueduct

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metencephalon - adults derivatives (wall and cavity)

wall: pons and cerebellum
cavity: upper part of fourth ventrivle

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myelencephalon - adults derivatives (wall and cavity)

wall: medulla
cavity: lower part of fourth ventricle

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neuroectoderm give rise to ... (cells)

1. CNS neurons
2. ependymal cell
3. oligodendroglia
4. astrocytes

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neural crest give rise to ... (cells)

1. PNS neurons
2. Schwann cells

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mesoderm give rise to ... (cells)

microglia

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neural tube defects - mechanism

Nuropores fail to fuse (4th week) --> persistent connection between amnionic cavity and spinal canal

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neuropoles fuse (when)

4th week

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causes of neural tube defects

low folic acid intake before conception and during pregnancy

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neural tube defects - labs

1. increased a-fetoprotein (AFP) in amniotic fluid and maternal serum (except spina bifida occulta)
2. increased acetylcholinesterase (AChE) in amniotic fluid in amniotic fluid (helpful confirmatory test)

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neural tube defects - increased acetylcholinesterase (AChE) in amnionic fluid - mechanism

fetal acetylcholinesterase (AChE) in CSF transudates across defect into amniotic fluid

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neural tube defects - increased in maternal blood and in amnitotic fluid

1. a-fetoprotein (AFP) --> both maternal blood and amniotic fluid
2. acetylcholinesterase (AChE) --> only amniotic fluid

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Spina bifida occulta - mechanism

failure of spinal canal to close but no stractural herniatiion, and intact dura --> associated with tuft of hair or skin dimple at level of bony defect

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Spina bifida occulta - area

usually at lower vertebral levels

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Spina bifida occulta - lab

normal AFP

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Spina bifida occulta - clinical appearance

it is associated with tuft of hair or skin dimple at level of bony defect

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Spina bifida - types and MC

1. Spina bifida occulta (MC)
2. Meningocele
3. Meningomyelocele

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Meningocele - mechanism

meninges (BUT NOT NEURAL TISSUE) herniate through body defect

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Meningomyelocele - mechanism

meninges and NEURAL TISSUE (eg. cauda equina) herniate through bony defect

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Meningocele - clinical appearance

+/- skin defect (and cyst through it)

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Meningomyelocele - clinical appearance

skin usually thin or absent (and cyst through it)

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Anencephaly - pathophysiology

malformation of anterior neural tube --> no forebrain, open calvarium

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Anencephaly - clinical and lab findings

1. open calvarium
2. polyhydramnios
3. increased AFP
4. frog like appearance of the fetus

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Anencephaly - lab

increased AFP

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Anencephaly - causes of polyhydramnios

no swallowing center in brain --> swallowing of amnionic fluid is impaired

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causes of anencephaly

1. maternal type 1 diabetes
2. low folic acid intake before conception and during pregnancy

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it decreases the risk of anencephaly

maternal folate supplementation

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Forebrain anomalies - types

1. anencephaly
2. holoprosencephaly

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holoprosencephaly - mechanism

failure of left and right hemispheres to separate during 5-6 weeks. Related to mutations in sonic hedgego signaling pathway

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holoprosencephaly - failure of left and right hemispheres to separate during

5-6 weeks

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holoprosencephaly - failure of left and right hemispheres to separate during 5-6 weeks. Related to mutations in

sonic hedgego signaling pathway

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holoprosencephaly - moderate form

cleft lip/palate

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holoprosencephaly - most severe form (and describe)

cyclopia --> only one eye, centrally placed at nose's root are. There is a missing nose or a nose in the form of a proboscis (a tubular appendage) located above the eye.

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holoprosencephaly - seen in

1. Patau syndrome
2. fetal alcohol syndrome

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neural tube defects - types

1. Spina bifida occulta
2. spina bifida (Meningocele, Meningomyelocele)
3. Anencephaly

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Posterior fossa malformations - types

1. Chiari II
2. Dandy-Walker

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Chiari II - pathophysiology

significant herniation of cerebellar tonsils and vermis through foramen magnum with aqueductal stenosis
--> hydrocephalus

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Chiari II - hydrocephalus - mechanism

aqueductal stenosis --> obstruction of CSF flow commonly

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Chiari II may occur in association with

1. lumbosacral menigomyelocele --> paralysis below the defect
2. syringomyelia

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Dandy-Walker - pathophysiology

agenesis of cerebellar vermis with cystic enlargment of 4th ventricle (fills the enlarged posterior fossa)

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Dandy-Walker is associated with

1. noncommunicating hydrocephalus
2. spina bifida

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syringomyelia - definition

cystic cavity within spinal cord (cystic degeneration of spinal cord)

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syringomyelia is associated with ...

1. Chiari malformations
2. trauma
3. tumors

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syringomyelia - MC area in the spinal cord

C8-T1

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syringomyelia - pathogenesis of symptoms

Crossing anterior spinal commissural fibers are typical damaged first

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syringomyelia - result in (clinical appearance)

cape like bilateral loss of pain and temperature sensation in upper extremities (FINE TOUCH SENSATION IS PRESERVED)

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Chiari I malformation - mechanism

cerebellar tonsillar ectopia >3-5 mm

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Chiari I malformation - clinical appearance

congenital, usually asymptomatic in childhood, manifests with feadaches and cerebellar sympotms (as the skull and brain are growing)

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Tongue development

1st and 2nd branchial arches form anterior 2/3
3rd and 4th branchial arches form posterior 1/3

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Tongue development - anterior 2/3 is formed by

1st and 2nd branchial arches

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nerves responsible for taste (only the names)

CN VII, IX, X (solitary nucleus)

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solitary nucleus - nerves

CN VII, IX, X

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nerves responsible for motor on the tongue (only the names)

CN X, XII

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nerves responsible for pain on the tongue (only the names)

CN V3, IX, X

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tongue - anterior 2/3 sensation

CN V3

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tongue - anterior 2/3 taste

CN VII

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tongue - posterior 1/3 sensation

mainly via CN IX, extreme posterior via CN X

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tongue - posterior 1/3 taste

mainly via CN IX, extreme posterior via CN X

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tongue - main muscles and function (and innervation)

1. hyoglossus (XII) --> retracts and depress tongue
2. genioglossus (XII) --> protrudes tongue
3. styloglossus (XII) --> draws sides of tongue upward to create a trough for swallowing
4. palatoglossus (X) --> elevates posterior tongue during swallowing

74

causes of anencephaly

1. maternal type 1 diabetes
2. low folic acid intake before conception and during pregnancy

75

holoprosencephaly - clinical presentation and mutation / seen in

moderate form --> cleft lip/palate
severe form --> cyclopia
mutation: sonic hedgego signaling pathway
seen in: 1. Patau syndrome 2. fetal alcohol syndrome

76

Chiari II may occur in association with

1. lumbosacral menigomyelocele --> paralysis below the defect
2. syringomyelia