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NEURO > Embryology of congenital malformations > Flashcards

Embryology of congenital malformations Flashcards

1
Q

what are the three germ layers of the epiblast embryologically

A

ectoderm
mesoderm
endoderm

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2
Q

what do each of the three germ layers go on to form

A

ectoderm

  • epidermis
  • nervous system

mesoderm

  • bone
  • muscle
  • blood cells, etc

endoderm

  • gut
  • pharynx
  • lungs
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3
Q

when does the CNS start to appear embryonically and what occurs at this time

A

beginning of the third week

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4
Q

how does the neural tube develop

A

thickening of the ectoderm anterior to primitive node = NEURAL PLATE

edges thicken and move up to form NEURAL FOLDS

neural folds migrate towards each other and fuse at midline = NEURAL TUBE

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5
Q

when do the anterior and posterior ends of the neural tube close

A

anterior (cranial/rostral) neuropore - 25 days

posterior (caudal) neuropore - 27 days

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6
Q

what does failure of the neural tube to close properly cause

A

neural tube defects

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7
Q

give 3 examples of neural tube defects

A

anencephaly
encephalocoele
spina bifida

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8
Q

what causes anencephaly

A

failure of the anterior neuropore to close

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9
Q

what are the consequences of anencephaly

A

skull fails to form
brain tissue degenerates
incompatible with life

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10
Q

what causes encephalocoele

A

failure of the rostral neural tube to close

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11
Q

what are the consequences of encephalocoele

A

herniation of cerebral tissue through a defect in the skull

most frequent in the occipital region

causes variable degrees of neurological deficits

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12
Q

what causes spina bifida

A

defective closure of the caudal neural tube

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13
Q

what are the consequences of spina bifida

A

affects the tissues overlying the spinal cord

causes non-fusion of the vertebral arches

neural tissue may or may not be affected

severity ranges from minor abnormalities to major clinical symptoms

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14
Q

what is the most minor form of spina bifida

A

spina bifida occulta

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15
Q

what occurs in spina bifida occulta

A

failure of embryonic halves of vertebral arch to grow and fuse

occurs in L5 and L6 vertebrae

usually no clinical symptoms

may result in dimple with small tuft of hair

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16
Q

what is spina bifida cystica

A

protrusion of the spinal cord and or/meninges through the defeat in the vertebral arches

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17
Q

what are the three types of spina bifida cystica

A

spina bifida with meningocele

spina bifida with meningomyelocele

myeloschisis

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18
Q

what occurs in meningocele

A

protrusion of meninges and cerebrospinal fluid

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19
Q

what occurs in meningomyelocle

A

nerve roots and/or spinal cord included in the protruding sac

neurological deficits - loss of sensation and muscle paralysis

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20
Q

what determines the area affected in meningomyelocle

A

the level of the lesion

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21
Q

what is meningomyelocle associated with

A

hydrocephalus

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22
Q

what occurs in myeloschisis

A

most severe form

spinal cord in affected area open due to failure of neural folds to fuse

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23
Q

what can decrease the risk of spina bifida during pregnancy

A

folic acid supplements

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24
Q

what types of prenatal diagnosis techniques are used for neural tube disorders

A

maternal blood screening
- high a-fetoprotein (AFP) in serum - leaks from foetal liver

amniocentesis
- high levels AFP in amniotic fluid

ultrasound

  • anencephaly from 12 weeks
  • spina bifida from 16-20 weeks
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25
Q

what are risk factors for neural tube disorders

A

genetic predisposition

nutrition - too like folate, too much vit A

environmental - hyperthermia

drugs - sodium valproate

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26
Q

when do the brain vesicles begin to form

A

begin with the closure of he anterior neuropore - 25 days

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27
Q

when do the 3 primary and 5 secondary vesicles form

A

primary - week 4

secondary week 5

28
Q

name the 3 primary vesicles

A

prosencephalon
mesencephalon
rhombencephalon

29
Q

name the 5 secondary vesicles

A 
telencephalon
diencephalon
mesencephalon
metencephalon
myelencephalon
30
Q

what are the three flexures (bends) of the embryological brain and when do they occur

A

cephalic - end week 3

cervical - end week 4

pontine - week 5

31
Q

where do the brain flexures occur

A

cephalic - between midbrain and hindbrain

cervical - between hindbrain and spinal cord

pontine - in hindbrain between metencephalon and myelencephalon

32
Q

what does the telencephalon go on to form

A

cerebral hemispheres, hippocampus, basal ganglia

33
Q

what does the diencephalon go on to form

A

thalamus, hypothalamus, pituitary gland, pineal

34
Q

what does the mesencephalon go on to form

A

midbrain, superior and inferior

colliculi

35
Q

what does the metencephalon go on to form

A

cerebellum, pons

36
Q

what does the myelencephalon go on to form

A

medulla

37
Q

what does the caudal neural tube go on to form

A

spinal cord

38
Q

what do the lumen of the neural tube go on to form

A

the ventricular system

39
Q

what parts of the neural tube lumen do the different ventricles form from

A

lateral - telencephalon

interventricular foramen -
telencephalon

3rd - diencephalon

cerebral aqueduct - mesencephalon

4th - metencephalon, myelencephalon

central canal - caudal end of neural tube

40
Q

when does CSF begin to form and where does it go

A

week 5

produced by choroid plexus

drains into subarachnoid space

absorbed into the venous system

41
Q

what is hydrocephalus

A

accumulation of cerebral spinal fluid

results in an enlarged brain and cranium

42
Q

what is the pathology of hydrocephalus

A

frequently due to blocked cerebral aqueduct

prevents CSF from lateral and 3rd passing into 4th

can’t drain properly

43
Q

what are the causes of hydrocephalus

A

genetic

prenatal viral infection

prenatal intraventricular haemorrhage

spina bifida cystica

44
Q

what occurs during cellular differentiation in the neural tube and when does it occur

A

neuronal cells made
- neurons and glia
cells connected together

starts in embryogenesis and continues postnatal

45
Q

what occurs at the cells of the neural tube

A

begin as a single layer of rapidly dividing neuroepithelial cells

pseudo stratified epithelium

divide at ventricular surface

46
Q

what CNS cells do neuroepithelial cells produce

A

neruons
astrocytes
oligodendrocytes

become ependymal cells once cell division finished

47
Q

what CNS cells are not produced by the neuroepithelial cells

A

microglia = mesenchymal cells that migrate to the CNS

48
Q

what do neural crest cells form

A

the cells of the PNS, autonomic nervous system

neurons and glia

49
Q

where does the sensory component of the nervous system grow from

A

grows from the neural crest

extend two processes

  • peripheral - body
  • central - dorsal horn of spinal cord
50
Q

where does the motor component of the nervous system grow from

A

grows from the neural tube

motor neruons

51
Q

how does the spinal cord position change throughout development

A

S1 at 3 months - extends entire length of vertebral column

L2/3 in newborns

L1 in adults

52
Q

what do the elongated spinal nerves from below the end of the spinal cord form

A

the caudal equina

53
Q

why does the position of the spinal cord change during development

A

the vertebral column and dura mater grow more rapidly than the spinal cord

54
Q

what forms the terminal filum

A

pia mater

55
Q

what forms the sympathetic and parasympathic ganglia and where do they end up

A

neural crest cells

sympathetic
- chains along spinal cord

parasympathetic
- near or within the nerves they innervate

56
Q

what is the surface of the cerebral hemispheres initially like

A

initially smooth

57
Q

what does rapid growth of the cerebral hemispheres result in

A

formation of sulk and gyro

pattern becomes more complex as the brain enlarges

58
Q

what is lissencephaly

A

“smooth brain”

rare brain disorder

gyri and sulci fail to develop

59
Q

what causes lissencephaly

A

caused by defective neuronal migration

60
Q

what does lissencephaly result in

A

severe mental impairment
failure to thrive
seizures
abnormal muscle tone

many affected children die before 10

61
Q

what is polymicrogyria and what can it cause

A

excessive number of small gyri

variable degree of neurological problems (e.g. mental retardation, seizures, motor defects, etc)

62
Q

what are some other congenital abnormalities

A

microcephaly - abnormally small head

aegenesi corpus
callosum - complete/partial absence of the corpus callosum

porencephaly - CSF filed cysts and cavities in cerebrum

schizencephaly - large clefts or slits in cerebrum

diastematomyelia - split cord malformation

63
Q

what can cause microcephaly and what are the impairments

A

genetic, drugs, infection (e.g. pika virus)

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

64
Q

what can cause porencephaly and what are the impairments

A

postnatal stroke or infection

Delayed growth and development, seizures, hypotonia, intellectual impairment

65
Q

what can cause schizencephaly and what are the impairments

A

genetic, in utero stroke, infection

paralysis, seizures, intellectual impairment, developmental delay

66
Q

what is diastematomyelia and what are the impairments

A

spinal cord splits longitudinally into two parts - usually associated with vertebral anomalies

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

67
Q

what can cause intellectual impairment

A

often no gross brain defects

  • genetic - downs syndrome
  • radiation
  • infection agents - rubella, toxoplasmosis, CMV
  • birth trauma
  • postnatal insults - head injury, infection (meningitis)

maternal alcohol abuse - foetal alcohol syndrome

NEURO (51 decks)

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