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Flashcards in Neurology - Embryology Deck (10):
1

Neural development

  • Notochord 
  • Neural plate
  • Orientation 
    • Alar plate
    • Basal plate

  • Notochord
    • Induces overlying ectoderm to differentiate into neuroectoderm and form the neural plate.
    • Notochord becomes nucleus pulposus of the intervertebral disc in adults.
  • Neural plate
    • Gives rise to the neural tube and neural crest cells.
  • Same orientation as spinal cord.
    • Alar plate (dorsal): sensory
    • Basal plate (ventral): motor

2

Regional specification of developing brain (444)

  • For each primary vescile
    • Other name
    • Secondary vesicles
  • Forebrain
  • Midbrain
  • Hindbrain

  • Forebrain (prosencephalon)
    • Telencephalon
    • Diencephalon
  • Midbrain (mesencephalon)
    • Mesencephalon
  • Hindbrain (rhombencephalon)
    • Metencephalon
    • Myelencephalon

3

Regional specification of developing brain (444):

  • For each secondary vesicle
    • Adult derivatives of walls
    • Adult derivatives of cavities
  • Telencephalon
  • Diencephalon
  • Mesencephalon
  • Metencephalon
  • Myelencephalon

  • Telencephalon
    • Walls: Cerebral hemispheres
    • Cavities: Lateral ventricles
  • Diencephalon
    • Walls: Thalamus
    • Cavities: Third ventricle
  • Mesencephalon
    • Walls: Midbrain
    • Cavities: Aqueduct
  • Metencephalon
    • Walls: Pons & Cerebellum
    • Cavities: Upper part of fourth ventricle
  • Myelencephalon
    • Walls: Medulla
    • Cavities: Lower part of fourth ventricle

4

CNS/PNS origins

  • Neuroectoderm
  • Neural crest
  • Mesoderm

  • Neuroectoderm
    • CNS neurons
    • Ependymal cells (inner lining of ventricles, make CSF)
    • Oligodendroglia
    • Astrocytes.
  • Neural crest
    • PNS neurons
    • Schwann cells.
  • Mesoderm
    • Microglia (like Macrophages, originate from Mesoderm).

5

Neural tube defects

  • Definition
  • Associations
  • Confirmatory test

  • Definition
    • Neuropores fail to fuse (4th week) Ž--> persistent connection between amniotic cavity and spinal canal.
  • Associations
    • Associated with low folic acid intake before conception and during pregnancy.
    • Elevated α-fetoprotein (AFP) in amniotic fluid and maternal serum. 
  • Confirmatory test
    • Increased acetylcholinesterase (AChE) in amniotic fluid is a helpful confirmatory test (fetal AChE in CSF transudates across defect into the amniotic fluid).

6

Neural tube defects

  • Spina bifida occulta
  • Meningocele
  • Meningomyelocele

  • Spina bifida occulta
    • Failure of bony spinal canal to close, but no structural herniation.
    • Usually seen at lower vertebral levels.
    • Dura is intact.
    • Associated with tuft of hair or skin dimple at level of bony defect.
  • Meningocele
    • Meninges (but not the spinal cord) herniate through spinal canal defect.
    • Normal α-fetoprotein (AFP).
  • Meningomyelocele
    • Meninges and spinal cord herniate through spinal canal defect.

7

Forebrain anomalies

  • Anencephaly
  • Holoprosencephaly

  • Anencephaly
    • Malformation of anterior neural tube resulting in no forebrain, open calvarium (“frog-like appearance”).
    • Clinical findings
      • Increased α-fetoprotein (AFP)
      • Polyhydramnios (no swallowing center in brain). 
    • Associated with maternal diabetes (type I).
    • Maternal folate supplementation decreased risk.
  • Holoprosencephaly
    • Failure of left and right hemispheres to separate
    • Usually occurs during weeks 5–6.
    • Complex multifactorial etiology that may be related to mutations in sonic hedgehog signaling pathway. 
    • Moderate form has cleft lip/palate, most severe form results in cyclopia.

8

Posterior fossa malformations

  • Chiari II (Arnold-Chiari malformation)
  • Dandy-Walker 

  • Chiari II (Arnold-Chiari malformation)
    • Significant herniation of cerebellar tonsils and vermis through foramen magnum with aqueductal stenosis and hydrocephalus.
    • Often presents with lumbosacral myelomeningocele and paralysis below the defect.
  • Dandy-Walker
    • Agenesis of cerebellar vermis with cystic enlargement of 4th ventricle (fills the enlarged posterior fossa).
    • Associated with hydrocephalus and spina bifida.

9

Syringomyelia

  • Definition
  • Findings

  • Definition
    • Cystic cavity (syrinx) within the spinal cord [A] (if central canal Ž--> hydromyelia).
    • Syrinx = tube, as in syringe
    • Most common at C8–T1
  • Findings
    • Crossing anterior spinal commissural fibers are typically damaged first.
    • Results in a “cape-like,” bilateral loss of pain and temperature sensation in upper extremities (fine touch sensation is preserved).
    • Associated with Chiari I malformation 
      • > 3–5 mm cerebellar tonsillar ectopia
      • Congenital, usually asymptomatic in childhood, manifests with headaches and cerebellar symptoms

10

Tongue development

  • Branchial arches
  • Muscles of the tongue are derived from...
  • Innervation
    • Taste
    • Pain
    • Motor

  • Branchial arches
    • 1st and 2nd branchial arches form anterior 2/3 (thus sensation via CN V3, taste via CN VII).
    • 3rd and 4th branchial arches form posterior 1/3 (thus sensation and taste mainly via CN IX, extreme posterior via CN X).
  • Muscles of the tongue are derived from...
    • Occipital myotomes.
  • Innervation
    • Taste—CN VII, IX, X (solitary nucleus).
    • Pain—CN V3, IX, X.
    • Motor—CN XII.

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