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Nervous System > Embryology and Congenital Malformations > Flashcards

Embryology and Congenital Malformations Flashcards

1
Q

When does the CNS begin to appear?

A

Beginning of 3rd week

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2
Q

What happens in the 3rd week?

A
  • Thickening of ectoderm anterior to the primitive node – NEURAL PLATE
  • Edges thicken and move upwards to form the NEURAL FOLDS
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3
Q

Describe the initial folding of the neural tube

A

Remains open at the anterior and posterior ends:
• Anterior (cranial) neuropore – closes 18-20 somite stage (25 days)
• Posterior (caudal) neuropore – closes day 27

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4
Q

When does the anterior neuropore close?

A

25 days

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5
Q

When does the posterior neuropore close?

A

Day 27

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6
Q

Describe the neural tube closure

A
  • Initiated at several points along anterior-posterior axis
  • Proceeds in cranial and caudal directions
  • Begins day 18 and completed by the end of the 4th week
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7
Q

What are the neural tube defects caused by the failure of the neural tube to close?

A
  • Anencephaly
  • Encephalocoele
  • Spina bifida
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8
Q

What is exencephaly / anencephaly (meroencephaly)?

A

Failure of the anterior neuropore to close, so neural tissue (brain and skull) left exposed to amniotic fluid causing it to degenerate

Incompatible with life
(Craniorachischisis – failure of neural tube closure along entire neuroaxis)

More common in females

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9
Q

What is encephalocoele?

A

Problem with fusion of skull so the cerebral tissue herniates through the skull

  • Most frequent in occipital region
  • Variable degree of neurological deficits
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10
Q

What is spina bifida?

A
  • Defective closure of the caudal neural tube
  • Affects tissues overlying the spinal cord
  • Non-fusion of the vertebral arches
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11
Q

What are four different types of spina bifida?

A
  • Spina Bifida Occulta
  • Spina Bifida Cystica
  • Spina Bifida with Meningocele
  • Spina Bifida with Meningomyelocle
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12
Q

What is spina bifida occulta?

A

Failure of embryonic halves of vertebral arch to grow normally and fuse

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13
Q

What are the features of spina bifida occulta?

A
  • Most minor form
  • Occurs in L5 and L6 vertebrae in 10% of healthy people
  • Usually no clinical symptoms
  • May result in dimple with small tuft of hair
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14
Q

What is spina bifida cystica?

A

Protrusion of spinal cord and/or meninges through the defect in the vertebral arches.

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15
Q

What is spina bifida with meningocele?

A

Protrusion of meninges and cerebrospinal fluid as the bones do not close around the spinal cord

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16
Q

What is spina bifida with meningomyelocle?

A
  • Nerve roots and/or spinal cord included in the sac
  • Spinal cord in affected area open due to failure of neural folds to fuse
  • Neurological deficits – loss of sensation and muscle paralysis
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17
Q

What are the features of spina bifida with meningomyelocle?

A
  • Area affected determined by level of lesion (loss of sensation and muscle paralysis)
  • Associated with hydrocephalus
  • Most severe form of myeloschisis
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18
Q

Why is the incidence of malformations in the UK decreasing?

A
  • Folic acid supplements

* Prenatal diagnosis - maternal blood screening, USS, amniocentisis

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19
Q

What do you look in maternal blood screening?

A

High levels α-fetoprotein (AFP) in serum – AFP from foetal liver leaks into amniotic fluid then into maternal blood

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20
Q

What can be seen in ultrasound scan for prenatal diagnosis?

A

Anencephaly from 12 weeks, spina bifida from 16-20 weeks

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21
Q

What is amniocentisis in prenatal diagnosis?

A

Diagnosis of chromosomal abnormalities and fetal infections, and also for sex determination.

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22
Q

Name three risk factors for congenital malformations

A
  • Genetic predisposition
  • Nutritional (i.e. too little folate, too much vit A)
  • Environmental (i.e. hyperthermia; takin certain drugs – i.e. sodium valproate)
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23
Q

Name the brain ventricle developed in the 4th week

A
  1. Prosencephalon (forebrain)
  2. Mesencephalon (midbrain)
  3. Rhombencephalon (hindbrain)
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24
Q

Name the five brain ventricles which are further developed from the initial three in the 5th week

A

Prosencephalon –>

  1. Telencephalon
  2. Diencephalon
  3. Mesencephalon

Rhombencephalon –>

  1. Metencephalon
  2. Myelencephalon
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25
Q

What are the three flexures during the folding of the embryo?

A
  • Cephalic flexure
  • Pontine flexure
  • Cervical flexure
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26
Q

What is the cephalic flexure?

A
  • End of 3rd week

* Between the midbrain (mesencephalon) and hindbrain (rhombencephalon)

27
Q

What is the cervical flexure?

A
  • End of 4th week

* Between the hindbrain and spinal cord

28
Q

What is the pontine flexure?

A
  • 5th week

* In hindbrain (between metencephalon and myecephalon)

29
Q

What structures develop from the telencephalon?

A
  • Cerebral hemispheres
  • Hippocampus
  • Basal ganglia
30
Q

What structures develop from the diencephalon?

A
  • Thalamus
  • Hypothalamus
  • Pituitary gland
  • Pineal
31
Q

What structures develop from the mesencephalon (midbrain)?

A

Superior and inferior colliculi

32
Q

What structures develop from the metencephalon?

A
  • Cerebellum

* Pons

33
Q

What structures develop from the myelencephalon?

A

Medulla

34
Q

What parts of the neural tube form the different parts of the ventricular system?

A
  • Telencephalon -> lateral ventricles
  • Diencephalon (bit of telen.) -> 3rd ventricles
  • Mesencephalon -> cerebral aqueduct
  • Metencephalon and myelencephalon -> 4th ventricle
  • End of neural tube -> central canal
35
Q

What connects the lateral and 3rd ventricles?

A

Intraventricular foramina

36
Q

When does CSF begin to form?

A

5th week by the choroid plexus in the ventricles

37
Q

How does the CSF drain?

A

Drains into subarachnoid space via opening in the roof of the 4th ventricle

Absorbed into venous system via arachnoid villi

38
Q

What is hydrocephalus?

A

Condition which causes the accumulation of CSF, abnormal production and resorption, that causes an enlarged brain and cranium.

39
Q

What is a common cause of hydrocephalus?

A

Frequently due to blocked cerebral aqueduct which prevents CSF from lateral and 3rd ventricles from passing into the 4th ventricle and therefore cannot drain out of the holes.

40
Q

Name four causes of hydrocephalus

A
  • Genetic
  • Prenantal viral infection
  • Intraventricular haemorrhage
  • Spina bifida cystica
41
Q

Describe the cellular differentiation in the neural tube

A
  • Needs to make neuronal cells (neurons and glia) and connect them together
  • Begins in early embryogenesis and continues into postnatal period
  • Some regions (i.e. olfactory epithelium) add new cells throughout life
42
Q

Describe the neural tube developing epithelium

A
  • Initially a single layer of rapidly dividing neuroepithelial cells
  • Pseudostratified epithelium
  • Divide at the ventricular surface
43
Q

Name the cells that develop from neuroepithelial cells

A
  • Neuron
  • Astrocyte
  • Oligodendrocyte

One the neuroepithelial cells have finished dividing they become ependymal cells

44
Q

What develops from the neural crest cells?

A

Peripheral nervous system (PNS) and the autonomic nervous system (neurones and glia).

They also form non-neuronal cells like melanocytes, adrenal medullar, meninges, facial bones/cartilage.

45
Q

What does the dorsal root ganglia contain?

A

Cell bodies on sensory neurons

46
Q

What do dorsal root ganglia develop from?

A

Neural crest cells

47
Q

What are the two process in the spinal nerve development?

A
  • Peripheral process -> body

* Central process -> dorsal horn of spinal cord (via dorsal roots)

48
Q

What do the motor and sensory components form from?

A
  • Motor component – motor neurons of spinal cord – formed by the neural tube
  • Sensory from neural crest cells
49
Q

What are the positional changes of the spinal cord that occur?

A
  • 3rd month – spinal cord extends entire length of vertebral column.
  • Vertebral column and dura mater grow more rapidly -> cord at progressively higher levels (newborn, ~L2 or L3; adult ~L1).
  • Initially spinal nerves found at level of origin.
  • Become elongated forming cauda equina (horses tail).
  • Pia mater forms terminal filum (long fibrous thread).
50
Q

What is cortical folding?

A

Surface of cerebral hemispheres are initially smooth and then begin to develop sulci (grooves) and gyri (elevations)

51
Q

What is the benefit of cortical folding?

A
  • Folding of brain save space and minimises brain volume
  • Bring together brain regions that would have otherwise been far apart – optimises brain wiring a functional organisation
52
Q

Name a congenital malformation caused by abnormal cortical folding

A
  • Lissencephaly (no cortical folding)

* Polymicrogyria (over folding)

53
Q

What are the features of lissencephaly?

A
  • Rare brain disorder
  • Caused by defective neuronal migration
  • Gyri and sulci fail to develop
  • Results in severe mental impairment, failure to thrive, seizures and abnormal muscle tone
54
Q

What is polymicrogyria?

A
  • Excessive number of small gyri

* Variable degree of neurological problems (i.e. mental retardation, seizures, motor deficits)

55
Q

Name four other congenital abnormalities?

A
  • Microcephaly
  • Aegenesis corpus callosum
  • Porencephaly
  • Schizencephaly
56
Q

What is microcephaly?

A

Head (circumference) is smaller than normal

  • Intellectual impairment
  • Delayed motor functions/speech
  • Hyperactivity
  • Seizures
  • Balance/co-ordination problems
57
Q

What are causes of microcephaly?

A

Genetic, drugs or infection (i.e. zika virus)

58
Q

What is aegenesis corpus callosum?

A

Complete or partial absence of the corpus callous

  • Effects range from subtle - severe
  • Cognitive and social difficulties -> intellectual impairment, seizures, hypotonia
59
Q

What is porencephaly?

A

CSF filled cysts or cavities within the cerebral hemisphere

• Delayed growth and development, seizures, hypotonia, intellectual impairment

60
Q

What is the cause of porencephaly?

A

Usually postnatal stroke or infection

61
Q

What is schizencephaly?

A

Large clefts or slits in the cerebral hemisphere

• Paralysis, seizures, intellectual impairment, developmental delay

62
Q

What are causes of schizencephaly?

A

Genetic, in utero stroke, infection

63
Q

What is diastematomyelia?

A
  • Spinal cord split longitudinally into two parts
  • Associated with vertebral abnormalities
  • Bone or cartilaginous process ‘fixes’ cord in place
  • Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation
64
Q

Name five causes of intellectual impairment

A

Often no obvious gross brain defects

  • Genetic (i.e. downs syndrome)
  • Radiation
  • Infectious agents (i.e. rubella, toxoplasmosis, cytomegalovirus)
  • Birth trauma (neurons due to the lack of O2)
  • Postnatal insults (i.e. head injury, infections (i.e. meningitis), lead exposure)

Common: maternal alcohol abuse -> foetal alcohol syndrome

Nervous System (47 decks)

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