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09. Year 2: Nervous System > Embryology and Congenital Malformations > Flashcards

Embryology and Congenital Malformations Flashcards

1
Q

The nervous system develops from what?

A

Embryonic ectoderm

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2
Q

The CNS appears when?

A

Beginning of week 3

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3
Q

What are the steps of neuralisation?

A
  1. Neural plate forms from thickening of the ectoderm anterior to the primitive node
  2. Neural folds form from the edges thickening and moving upwards
  3. Neural folds migrate towards each other and fuse at midline forming neural tube, which remains open at anterior and posterior ends
  4. Neural tube closure
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4
Q

What does the neural plate form from?

A

Thickening of the ectoderm anterior to the primitive node

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5
Q

Describe the process of neural tube closure?

A
  • Initiated at several points along A-P axis
  • Proceeds in cranial and caudal directions
  • Begins on day 18 and is completed by end of 4th week (about day 27)
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6
Q

What does failure of the neural tube to close correctly lead to?

A

Failure to close properly leads to neural tube defects (NTDs):

  • Anencephaly
  • Encephalocoele
  • Spina bifida

The are some of the most common congenital abnormalities of the CNS

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7
Q

How many closure sites of the neural tube are there in humans?

A

Up to 5

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8
Q

Describe the epidemiology of exencephaly/ancenephaly?

(incidence, sex)

A

1:1500 births (4x more common in females)

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9
Q

Describe the pathology of exencephaly/anencephaly?

A

Failure of anterior neuropore to close

Skull fails to form

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10
Q

Describe the prognosis of exencephaly/anencephaly?

A

Brain tissue degenerates, is incompatible with life

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11
Q

What is craniorachischisis?

A

Craniorachischisis = failure of neural tube closure along entire neuroaxis

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12
Q

Describe the epidemiology of encephalocoele?

(incidence)

A

1:4000 births

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13
Q

Describe the pathology of encephalocoele?

A
  • Herniation of cerebral tissue through a defect in the skull
  • Failure in closure of rostral neural tube
  • Most frequently in occipital region
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14
Q

Describe the prognosis of encephalocoele?

A

Variable degree of neurological deficits

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15
Q

Describe the pathology of spina bifida?

A
  • Defective closure of the caudal neural tube
  • Affects tissues overlying the spinal cord
  • Neural tissue may or may not be affected
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16
Q

What is spinda bifida?

A

Spina bifida = non-fusion of vertebral arches

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17
Q

Describe the prognosis of spina bifida?

A

Severity ranges from minor abnormalities to major clinical symptoms

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18
Q

What are the different kinds of spina bifida?

A
  • Spina bifida occulta
    • Most minor form
    • Failure of embryonic halves of vertebral arch to grow normally and fuse
    • Occurs in L5 and L6 vertebrae
    • Usually no clinical symptom
    • May result in dimple with small tuft of hair
  • Spina bifida cystica
    • Protrusion of spinal cord and/or meninges through the defects in vertebral arches
    • 1:1000 births
    • Different kinds
      • Spina bifida with meningocele
        • Rarest form
        • Protrusion of meninges and CSF
      • Spina bifida with meningomyelocle
        • Nerve roots and/or spinal cord included in the sac
        • Neurological deficits such as loss of sensation and muscle paralysis
        • Area affected determined by level of lesion
        • Often associated with hydrocephalus
      • Myeloschisis
        • Most severe form
        • Spinal cord in affected area open due to failure of neural folds to fuse
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19
Q

Spina bififa occulta - pathology

A
  • Most minor form
  • Failure of embryonic halves of vertebral arch to grow normally and fuse
  • Occurs in L5 and L6 vertebrae
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20
Q

Spina bifida occulta - presentation

A
  • Usually no clinical symptom
  • May result in dimple with small tuft of hair
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21
Q

Spina bifida cystica - pathology

A
  • Protrusion of spinal cord and/or meninges through the defects in vertebral arches
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22
Q

Spina bifida cystica - epidemiology (incidence)

A
  • 1:1000 births
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23
Q

Spina bifida cystica - different kinds

A
  • Spina bifida with meningocele
    • Rarest form
    • Protrusion of meninges and CSF
  • Spina bifida with meningomyelocle
    • Nerve roots and/or spinal cord included in the sac
    • Neurological deficits such as loss of sensation and muscle paralysis
    • Area affected determined by level of lesion
    • Often associated with hydrocephalus
  • Myeloschisis
    • Most severe form
    • Spinal cord in affected area open due to failure of neural folds to fuse
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24
Q

Is incidence of neurological congenital malformations increasing or decreasing? Why?

A

Incidence is decreasing in the UK due to:

  • Folic acid supplements (400ug/day)
  • Prenatal diagnosis
    • Maternal blood screening
      • Indicated by high levels of α-fetoprotein (AFP) in serum – AFP from foetal liver leaks into amniotic fluid then into maternal blood.
      • Best detected 16-20 weeks
    • Amniocentesis
      • High levels of AFP in amniotic fluid
    • Ultrasound
      • Anencephaly from 12 weeks, spina bifida from 16-20 weeks
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25
What are risk factors for neurological congenital malformations?
* Genetic predisposition * Nutritional (such as too little folate, too much vitamin A) * Environmental (such as hyperthermia, taking certain drugs)
26
What does development of brain vesicles begin with?
Begins with closure of anterior neuropore (about day 25, 18-20 somite stage)
27
What bends in the neural tube occur?
* Cephalic flexure * End of 3rd week * Between midbrain (mesencephalon) and hindbrain (rhomboencephalon) * Cervical flexure * End of 4th week * Between hindbrain and spinal cord * Pontine flexure * 5th week * In hindbrain (between metencephalon and myelencephalon)
28
29
Where do the following bends occur: - cephalic flexure - cervical flexure - pontine flexure
* Cephalic flexure * Between midbrain (mesencephalon) and hindbrain (rhomboencephalon) * Cervical flexure * Between hindbrain and spinal cord * Pontine flexure * Between metencephalon and myelencephalon)
30
What forms the ventricular system?
Lumen of neural tube
31
What are the 3 primary brain vesicles?
* Prosencephalon (forebrain) * Mesencephalon (midbrain) * Rhombencephalon (hindbrain)
32
What is the forebrain formed from?
Prosencephalon
33
What is the midbrain formed from?
Mesencephalon
34
What is the hindbrain formed from?
Rhomboencephalon
35
What are the 5 secondary brain vesicles?
* Telencephalon * Diencephalon * Mesencephalon * Metencephalon * Myelencephalon
36
What do the following develop from: - telencephalon - diencephalon - mesencephalon - metencephalon - myelencephalon
* Prosencephalon * Telencephlon * Diencephalon * Mesencephalon remains the same, is a primary and secondary brain vesicle * Rhombencephalon * Metencephalon * Myelencephalon
37
What do the following develop from: - lateral ventricle - III ventricle - Cerebral aqueduct - IV ventricle
* Lateral ventricle * Telencephalon * III ventricle * Telencephalon/diencephalon * Cerebral aqueduct * Mesencephalon * IV ventricle * Metencephalon/myelencephalon
38
When does CSF production begin?
* Begins for form during 5th week
39
What is CSF originally produced and drained by?
* Produced predominately by choroid plexus (in 3rd, 4th, lateral ventricles) * Drains into subarachnoid space via openings in roof of 4th ventricle * Absorbed into venous system
40
What is an example of congenital malformation to do with CSF?
Hydrocephalus
41
Hydrocephalus - pathology
* Accumulation of cerebrospinal fluid * Results in enlarged brain and cranium * Frequently due to blocked aquaduct * Prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle, so cant drain properly
42
Hydrocephalus - aetiology
* Frequently due to blocked aquaduct * Genetic * Prenatal viral infection or intraventricular haemorrhage * Spina bifida cystica
43
44
When does cellular differentiation in the neural tube begin and end?
* Need to make neuronal cells (glia and neurons) and connect cells together * Begins in early embryogenesis, continues into postnatal period * Some regions (such as olfactory epithelium) add new cells throughout life
45
What cells does the neuroepithelium produce?
* Most cells of CNS * Exception is microglia, which is formed by mesenchmal cells that migrate to CNS
46
What does microglia form from?
Formed by mesenchymal cells and migrates to CNS
47
What do neural crest cells go onto form?
Cells of PNS, autonomic nervous system (neurons and glia) Also forms non-neuronal cells such as: * Melanocytes * Adrenal medulla * Meninges * Facial bones/cartilage
48
What are meninges formed from?
Neural crest cells
49
What are examples of neural crest cell derivatives?
* Sensory neurons * Autonomic neurons (sympathetic and parasympathetic ganglia) * Schwann cells + satellite cells of ganglia * Aortic plexuses (nerves surrounding the aorta) * Endocrine cells (chromaffin cells of adrenal medulla; calcitonin producing cells of carotid body; parafollicular cells of thyroid). * Enteric nervous system * Pigment cells (melanocytes) – all pigment except RPE * Leptomeninges of anterior brain (prosencephalon and part of mesencephalon) * Non-neural head structures (including bone, cartilage and connective tissue). * Teeth (dental papilla; odontoblasts) * Iris muscle and pigment; ciliary muscles * Corneal stroma * Inner ear development * Regions of the heart + walls of large arteries
50
What are PNS neurons formed from?
Migrating neural crest cells
51
What is glia formed from?
Migrating neural crest cells
52
Decribe spinal nerve development?
* Dorsal root ganglion (DRG, spinal ganglia) is a sensory component * Formed from neural crest * Extend two processes * Peripheral process forms body * Central process forms dorsal horn of spinal cord (via dorsal roots) * Motor component is motor neurons of spinal cord (formed from neural tube)
53
What are the following formed from: - dorsal root ganglion - motor neuron of spinal cord
* Dorsal route ganglion * Neural crest * Motor neuron of spinal cord * Neural tube
54
What positional changes occur in the spinal cord?
* 3rd month extends entire length of vertebral column * Vertebral column and dura mater grow more rapidly, cord at progressively higher levels (newborn is about L2 or L3, adult is about L1) * Initially spinal nerves found at level of origin * Become elongated forming cauda equina * Pia mater forms terminal filum (long fibrous thread)
55
Describe the process of cortical folding?
* Surface of cerebral hemispheres initially smooth * Develop sulci (grooves) and gyri (elevations) * Pattern becomes more complex as development proceeds * Is done to save space and minimise the brains volume * Brings together brain regions that would otherwise be far apart: * Optimised brain wiring and functional organisation
56
What are some examples of neurological congenital abnormalities?
* Lissencephaly * Polymicrogyria * Microecephaly * Aegenesis corpus collosum * Porencephaly * Schizencephaly * Diastermatomyelia * Intellectual impairment
57
Lissencephaly - pathology
* Rare brain disorder * Caused by defective neuronal migration * Gyri and sulci fail to develop
58
Lissencephaly - complications
* Results in severe mental impairment, failure to thrive, seizures and abnormal muscle tone * Many affected children die before age 10
59
Polymicrogyria - pathology
* Excessive number of small gyri
60
Polymicrogyria - complications
* Variable degree of neurological problems (such as mental retardation, seizures, motor deficits etc)
61
Microecephaly - aetiology
* Genetic, drugs, infection (such as Zika virus)
62
Microecephaly - complications
* Intellectual impairment, delayed motor function/speech, hyperactivity, seizures, balance/co-ordination problems
63
Aegenesis corpus collosum - complications
* Alone or with other cerebral abnormalities * Effects range from subtle to severe * Cognitive and social difficulties causing intellectual impairment, seizures, hypotonia
64
Porencephaly - pathology
Usually from postnatal stroke or infection
65
Porencephaly - complications
* Delayed growth and development, seizures, hypotonia, intellectual impairment
66
Schizencephaly - aetiology
* Genetic, in ureto stroke, infection
67
Schizencephaly - complications
* Paralysis, seizures, intellectual impairment, developmental delay
68
Diastematomyelia - pathology
Diastematomyelia (split cord malformation): * Spinal cord split longitudinally into 2 parts * Usually associated with vertebral anomalies * Bony or cartilaginous process “fixes” cord into place
69
Diastematomyelia - complications
* Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation
70
Intellectual impairment - aetiology
* Often no obvious gross brain defects * Causes * Genetic (such as Down’s syndrome) * Radiation * Infectious agents (such as rubella, toxoplasmosis, cytomegalovirus) * Birth trauma * Postnatal insults (such as head injury, infections such as meningitis, lead exposure) * Maternal alcohol abuse (very common cause) * Foetal alcohol syndrome 1:1000 * Estimated up to 1:100 show some degree of intellectual impairment

09. Year 2: Nervous System (48 decks)

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