Embryology Flashcards

1
Q

What is spina bifida? What are the different types?

A

Spina bifida cystica = failure of neural tube to close caudally —-> part of spinal cord/meninges herniates through the incomplete vertebral column and is exposed (cyst - no skin covering)

  • can occur anywhere along the length of the spinal cord (most commonly in lumbo-sacral region)
  • neurological deficits occur (but not cognitive delay - this would be caused by associated hydrocephalus)
  • hydrocephalus nearly always occurs

Spina bifida occulta = failure of L5/S1 vertebral arches to close - covered by skin +/- tuft of hair (usually asymptomatic)
- 25% incidence

note: myelomeningocoele = cyst contains meninges and neural tissue (neural problems and life-threatening infections)

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2
Q

What is anencephaly?

A

Failure of neural tube to close cranially

Absence of cranial structures, therefore incompatible with life

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3
Q

What results from complete failure of the neural tube to close?

A

Rachischisis

Splayed open nervous system

Caused by failed neural fold elevation

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4
Q

How are neural tube defects diagnosed? How can the risk of neural tube defects be reduced?

A

Increase in maternal serum alpha-fetoprotein (indicates any kind of open defect)

Ultrasound-guided sonography

Folic acid supplementation for 3 months pre- & post- conception reduces the incidence of neural tube defects by 70%

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5
Q

Outline spinal cord development.

A

3rd month = spinal cord is same length as vertebral column

3 months + = vertebral column grows faster, pulling the spinal roots (exiting the vertebral column via intervertebral foramina) down —> cauda equina created (collection of spinal roots descending from the lower spinal cord and occupying the vertebral column below the spinal cord)

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6
Q

Outline development of the brain.

A

4th week = dilations at cranial end of closed neural tube —> three primary brain vesicles (forebrain, midbrain, hindbrain)

5 weeks = primary brain vesicles become 5 secondary vesicles

  • FOREBRAIN = telencephalon & diencephalon
  • MIDBRAIN = mesencephalon
  • HINDBRAIN = metencephalon & myelencephalon
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7
Q

Outline the development of the neurological flexures.

A

Cranial neural tube development & growth exceeds available space, therefore must fold

CERVICAL FLEXURE = spinal cord-hindbrain junction

CEPHALIC FLEXURE = midbrain region

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8
Q

Outline the development of the ventricular system.

A

Neural tube not occluded during development —> in newborn forms interconnected reservoirs of CSF

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9
Q

What is hydrocephalus? What are the causes of hydrocephalus?

A

HYDROCEPHALUS = abnormal expansion of ventricles within the brain caused by accumulation of CSF

Congenital = obstruction of cerebral aqueduct (aqueductal stenosis)
Acquired: 
- spina bifida cystica 
- intraventricular haemorrhage 
- meningitis 
- tumours
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10
Q

How is the neural tube organised?

A
Roof plate 
Alar plate (sensory ---> dorsal horn)
Sulcus limitans (boundary between alar & basal plates) 
Basal plate (motor ---> ventral horn)
Floor plate
Inner = neuroepithelial layer 
Middle = intermediate (mantle) layer of neuroblasts 
Outer = marginal layer (processes)
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11
Q

Outline neural crest migration. Give some examples of disorders caused by disrupted neural crest migration.

A

Cells of lateral border of neuroectoderm tube displaced and enter the mesoderm —> become mesenchyme

Neural crest cell derivatives =

  • dorsal root ganglion
  • sympathetic ganglion
  • suprarenal glands
  • preaortic ganglia
  • enteric ganglia

Foetal alcohol syndrome
Hirschsprung’s disease = aganglionic megacolon (single component affected)
DiGeorge syndrome = thyroid deficiency, immunodeficiency secondary to thymus defect, cardiac defects, abnormal facies (multiple components affected)

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12
Q

What is the notochord? How is the neural plate induced to elevate its lateral edges?

A

NOTOCHORD = solid cord of cells formed by the prenotochord cells migrating through the primitive pit
- basis for midline, axial skeleton, & neuraltube

Notochord initiates induction of neural plate —> thickening of ecotderm & specialisation into neuroectoderm —> formation of neural folds —> neural folds fuse to form neural tube (cranial end fuses before caudal end)

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13
Q

How is hydrocephalus corrected after birth?

A

Divert excess CSF into the peritoneum via ventriculo-peritoneal shunt

OR into atrium of the heart via ventriculo-atrial shunt

OR into jugular vein

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