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MBChB - Y2 - Systems - Nervous System > Embryology and Congenital Malformations > Flashcards

Embryology and Congenital Malformations Flashcards

1
Q

Which nerve layer does the nervous system develop from?

A

The embryonic ectoderm

Also forms the epidermis

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2
Q

How is the neural plate formed?

A

Thickening of ectoderm anteroir to the primitive node

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3
Q

How are neural folds formed?

A

Edges thicken and move upwards to form neural folds

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4
Q

How is the neural tube formed?

A

Neural folds migrate towards each other and fuse at the midline

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5
Q

When do the anterior and posterior neural tube openings open/close?

A
  • Anterior (cranial/rostral) neuropore closes 18 – 20 somite stage (~25 days)
  • Posterior (caudal) neuropore closes ~ day 27.
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6
Q

At what point is the nervous system in open communication with the amniotic fluid?

A

When the neuropores are still open

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7
Q

What are the neural tube defects which happen as a result of failure of the neural tube to close properly?

A

Anencephaly

Encephalocoele

Spina Bifida

(Some of the most common congenital abnormalities of the CNS)

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8
Q

What causes anencephaly?

A

Failure of the anterior neuropore to close

Skull fails to form

Brain tissue degenerates

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9
Q

What is craciorachischisis?

A

failure of neural tube closure along entire neuroaxis

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10
Q

What is the cause of encephalocele?

A

Failure in closure rostral neural

Results in herniation of cerebral tissue through a defect in the skull (most likely to be in the occipital region)

Variable degree of neurological defecits

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11
Q

What cause spina bifida?

A
  • Defective closure of the caudal neural tube
  • Affects tissues overlying the spinal cord
  • Spina bifida = non-fusion of vertebral arches.
  • Neural tissue may or may not be affected
  • Severity ranges from minor abnormalities to major clinical symptoms.
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12
Q

What is the most minor form of spina bifida?

A

Spina bifida occulta

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13
Q

What causes spina bifida occulta?

A
  • Failure of embryonic halves of vertebral arch to grow normally and fuse.
  • Occurs in L5 and L6 vertebrae of 10% of otherwise healthy people.
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14
Q

What are the clinical features of spina bifida?

A

Asymptomatic

May result in a dimple with a small patch of hair

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15
Q

What causes spina bifida cystica?

A

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

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16
Q

What causes spina bifida with meningocele (form of spina bifida cystica)

A

Protrusion of meninges and cerebrospial fluid

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17
Q

What causes Spina bifida with meningomyelocle (form of spina bifida cystica)

A

•Nerve roots and/or spinal cord included in the sac (that protrudes through the defect in the vertebral arches)

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18
Q

What are teh features of spina bifida with meningomyelocle?

A
  • Neurological deficits – loss of sensation and muscle paralysis
  • Area affected determined by level of lesion
  • Often associated with hydrocephalus
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19
Q

What is the most severe form of spina bifida?

A

Myeloschisis

•Spinal cord in affected area open due to failure of neural folds to fuse.

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20
Q

How do we help to prevent spina bifida?

A

Folic acid supplements for pregnant women

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21
Q

How is prenatal diagnosis of spina bifida achieved?

A

Maternal blood screening for AFP (alpha fetoprotein) in serum

Best detected 16 - 20 weeks

Amniocentesis (high levels of AFP in amniotic fluid)

Ultrasound - anencephaly from 12 weeks and spina bifida from 16 - 20

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22
Q

What are the risk factors for spina bifida?

A
  • Genetic predisposition
  • Nutritional (e.g. too little folate, too much vitamin A)

Vitamin A is avoided by women – found in the liver. Vitamin A is converted into another compound in the body which is a teratogen

•Environmental (e.g. hyperthermia; taking certain drugs – e.g. sodium valproate)

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23
Q

When does development of brain vesicles begin?

A

With closure of anterior neuropore (around day 25)

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24
Q

What are the 3 primary brain vesicles and what are the 5 seconday brain vesicles that form from these?

A
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25
Q

Where do you find the cephalic flexure, the cervical flexure and the pontine flexure?

A

Cephalic flexure - Between midbrain (mesencephalon) and hindbrain (rhombencephalon)

Cervical flexure - between hindbrain and spinal cord

Pontine flexure - between metencephalon and myeloencephalon

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26
Q

When do the different flexures form?

A

Cephalic flexure - end of 3rd week

Cervical flexure - end of 4th week

Pontine flexure - 5th week

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27
Q

What forms from the diencephalon?

A

thalamus, hypothalamus, pituitary gland, pineal

28
Q

What forms from the telencephalon?

A

Cerebral hemispheres

Hippocampus

Basal ganglia

29
Q

What forms from the midbrain?

A

Superior and inferior colliculi

30
Q

What forms from the metencephalon?

A

Cerebellum and pons

31
Q

What forms from the myelencephalon?

A

The medulla

32
Q

What forms the ventricular system in the brain?

A

The lumen of the neural tube

33
Q

Where is CSF produced?

A

Predominately by the choroid plexus in the 3rd and 4th ventricles

34
Q

Where does CSF drain?

A

Drains into the subarachnoid space via openings in roof of 4th ventricle and absorbed into the venous system

35
Q

What causes hydrocephalus?

A

Accumulation of CSF

Frequently due to blocked aqueduct - prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle - can’t drain properly

36
Q

What are the causes of hydrocephalus?

A

Genetic

Prenatal viral infection or intraventricular haemorrhage

Spina bifida cystica

37
Q

What cell type makes up the initial neural tube?

A

Rapidly dividing neuroepithelial cells

38
Q

What types of cells do neuroepithalial cells form in the CNS?

A

Forms all the cells in the CNS apart from microglia

(neurons, astrocytes, oligodendrocytes, ependymal cells)

39
Q

Where do neural crest cells arise from?

A

They are part of the roof plate of the neural tube

40
Q

What is the action of the neural crest cells?

A

Undergo an epithelial to mesenchymal transition, delaminating from the neuroepithelium and migrating through the periphery where they differentiate into varied cell types.

41
Q

What cell types do neural crest cells form?

A

They give rise rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia

Neural crest cells form all the pigment in our body apart from the pigment in our eye

42
Q

Each spinal nerve has a motor component and a sensory component, what is the embryological origin of both of these?

A

Sensory - cell bodies of dorsal root ganglia, arise from neural crest cells

Motor - Comes from motor neurones which are a neural tube derived cells - they line the ventral part of the neural tube, they extend their axons out via the ventral root where it meets the dorsal root to form the spinal nerve

43
Q

What causes the spinal cord to ascend the vertebral column with age?

A

The vertebral column and the dura mater grow more rapidly

44
Q

What forms the sympathetic and parasympathetic ganglia?

A

Neural crest cells

45
Q

Where do you find sympathetic ganglia?

A

Chains along side the spinal cord (paravertebral)

Preaortic ganglia

Sympathetic organ plexuses (in heart, lungs GI tract)

46
Q

Where do you find parasympathetic ganglia?

A

Near or within the organs they innervate

47
Q

What causes the development of sulci and gyri in the brain?

A

The surface of cerebral hemispheres is initially smooth - rapid growth results in the development of sulci and gyri

The pattern becomes more complex as the brain enlarges

48
Q

What is lissenceohaly?

A

Smooth brain

Defective neuronal migration

Gyri and sulci fail to develop

49
Q

What are the health implications of lissencephaly?

A
  • Gyri and sulci fail to develop
  • Results in severe mental impairment, failure to thrive, seizures, and abnormal muscle tone.
  • Many affected children die before age 10.
50
Q

What is polymicrogyria?

A

Excessive number of small gyri

•Variable degree of neurological problems (e.g. mental retardation, seizures, motor deficits etc)

51
Q

What are the causes of microcephaly?

A

Genetic

Drugs

Infection

52
Q

What is the effect of microcephaly on the person?

A

•Intellectual impairment, delayed motor functions/speech, hyperactivity, seizures, balance/co-ordination problems etc.

53
Q

What are the effects of agenesis of corpus callosum?

A

May come with ither cerebral abnormalities

  • Effects range from subtle – severe
  • Cognitive and social difficulties - intellectual impairment, seizures, hypotonia etc
54
Q

What is porencephaly?

A

CSF filled cysts or cavities

55
Q

What causes porencephaly?

A

Usually from postnatal stroke or infection

56
Q

What is the result of porencephaly on the person?

A

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

57
Q

What is schizencephaly characterised by?

A

Large clefts or slits

58
Q

What causes schizencephaly?

A

Genetic

In utero stroke

Infection

59
Q

What is the effect of schizencephaly?

A

Paralysis, seizures, intellectual impairment, developmental delay

60
Q

What is the name given to the condition resulting in split cord malformation?

A

Diastematomyelia - the chord is split longitudinally into 2 parts

61
Q

What fixes the cord in one place in diastematomyelia?

A

Bony or cartilaginous process - fixes the cord in one place

62
Q

What is the impact of diastematomyelia?

A

•Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation.

63
Q

What are the causes of intellectual impairment?

A

Genetic

Radiation

Infectious agents

Birth trauma

Postnatal insults

COMMON CAUSES - Maternal alcohol abuse

64
Q

What are the infectious agents that cause intellectual impairment?

A

Rubella

Toxoplasmosis

Cytomegalovirus

65
Q

What postnatal insults can result in intellectual impairment?

A

Head injury

Infections (meningitis)

Leads exposure

MBChB - Y2 - Systems - Nervous System (48 decks)

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