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year 2 neuro - Robbie > Embryology and Congenital Malformations > Flashcards

Embryology and Congenital Malformations Flashcards

1
Q

Nervous system develpos form the embryonic __________

A

ectoderm

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2
Q

CNS appears at the beginning of the _____ week

A

3rd

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3
Q

Thickening of ectoderm anterior to the primitive node leads to the formation of what?

A

neural plate

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4
Q

edges of the neural plate thicken and move upwards to form what?

A

neural folds

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5
Q

Neural folds migrate towards each other and fuse at midline forming the _________

A

neural tube

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6
Q

Where does the neural tube originally remain open at?

A

anterior and posterior ends

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7
Q

When do the anterior and posterior ends close?

A

Anterior (cranial/rostral) neuropore closes 18 – 20 somite stage (~25 days)

Posterior (caudal) neuropore closes ~ day 27

(neuropore - either of the openings to the exterior at the anterior and posterior ends of the neural tube of a vertebrate embryo)

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8
Q

The neural plate goes on to form what?

A

neural tube

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9
Q

What is closure of the neural tube essential for?

A

normal development and function

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10
Q

What is the process of the neural tube closing?

A

Initiated at several points along A-P axis

Proceeds in cranial and caudal directions

Begins day 18

Completed by end of 4th week (~day 27)

Up to 5 closure sites in humans

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11
Q

Failure of neural tube to close properly results in neural tube defects (NTDs), what are some examples?

A
  • Anencephaly
  • Encephalocoele
  • Spina bifida
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12
Q

What is Anencephaly?

A

Failure of anterior neuropore to close

Skull fails to form

Brain tissue degenerates

Incompatible with life

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13
Q

How common is Anencephaly?

A

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

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14
Q

What is Craniorachischisis?

A

failure of neural tube closure along entire neuroaxis

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15
Q

What is Encephalocoele?

A

Herniation of cerebral tissue through a defect in the skull

Failure in closure of rostral neural tube

Most frequent in occipital region

Variable degree of neurological deficits

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16
Q

How common is Encephalocoele?

A

1:4000 births

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17
Q

What is 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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18
Q

What is spina bifida occulta?

A

Most minor form of spina bifida

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

Occurs in L5 and L6 vertebrae of 10% of otherwise healthy people

Usually no clinical symptoms

May result in dimple with small tuft of hair

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19
Q

What is spina bifida cystica?

A

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

1:1000 live births

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20
Q

What is spina bifida with meningocele?

A

rarest form

protrusion of meninges and cerebrospinal fluid

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21
Q

What is spina bifida with meningomyelocle?

A

Nerve roots and/or spinal cord included in the sac

Neurological deficits - loss of sensation and muscle paralysis

Area affected determined by level of lesion

Often associated with hydrocephalus (a condition in which excess cerebrospinal fluid (CSF) builds up within the ventricles)

Most severe form is myeloschisis. Spinal cord in affected area open due to failure of neural folds to fuse

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22
Q

How are neural tube defects prevented?

A

Folic acid supplements (400 µg/day - 50-70% decrease in risk)

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23
Q

How is a prenatal diagnosis made of neural tube defects?

A

Maternal blood screening - Indicated by high levels 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 AFP in amniotic fluid)

Ultrasound (Anencephaly from 12 weeks, spina bifida from 16-20 weeks)

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24
Q

What are the risk factors for neural tube defects?

A

Genetic predisposition

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

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

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25
Q

What is A?

A

Prosencephalon

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26
Q

What is B?

A

Mesencephalon

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27
Q

What is C?

A

Rhombencephalon

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28
Q

A?

A

Telencephalon

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29
Q

B?

A

Diencephalon

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30
Q

C?

A

Metencephalon

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31
Q

D?

A

Myelencephalon

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32
Q

How many primary and how many secondary brain vesicles are there?

A

3 primary and 5 secondary

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33
Q

What are the 3 flextures seen in the developing embryo, when do they develop and where are they?

A

Cephalic flexure - End of 3rd week. Between midbrain (mesencephalon) and hindbrain (rhombencephalon)

Cervical flexure - End of 4th week. Between hindbrain and spinal cord

Pontine flexure - 5th week. In hindbrain (between metencephalon and myelencephalon)

34
Q

A?

A

Prosencephalon

35
Q

B?

A

Diencephalon

36
Q

C?

A

telencephalon

37
Q

D?

A

Mesencephalon

38
Q

E?

A

Rhombencephalon

39
Q

F?

A

metencephalon

40
Q

G?

A

myelencephalon

41
Q

What does the telencephalon form

A

cerebral hemispheres, hippocampus, basal ganglia

42
Q

What does the Diencephalon form?

A

thalamus, hypothalamus, pituitary gland, pineal

43
Q

What does the Mesencephalon form?

A

superior and inferior colliculi

44
Q

What does the metencephalon form?

A

cerebellum, pons

45
Q

What does the myelencephalon form?

A

medulla

46
Q

The lumen of the neural tube forms the ventricular system, what does the Telencephalon form

A

lateral ventricles

47
Q

The lumen of the neural tube forms the ventricular system, what does the Diencephalon form

A

3rd ventricle

48
Q

The lumen of the neural tube forms the ventricular system, what does the Mesencephalon form

A

cerebral aqueduct

49
Q

The lumen of the neural tube forms the ventricular system, what does the Metencephalon and Myelencephalon form

A

4th ventricle

50
Q

When is CSF formed, what is it made by, and where does it drain?

A

Begins to form during 5th week

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

51
Q

What is an accumulation of cerebral spinal fluid called?

A

Hydrocephalus

52
Q

What does hydrocephalus, reason for it happening and its causes

A

Results in enlarged brain and cranium

Frequently due to blocked aqueduct

Prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle - can’t drain properly

Causes: genetic, prenatal viral infection or intraventricular haemorrhage, spina bifida cystica

53
Q

Cellular differentiation happens in the neural tube, itially what is formed?

A

Initially a single layer of rapidly dividing neuroepithelial cells

Pseudostratified epithelium

Divide at ventricular surface

54
Q

What produces most cells of the CNS?

A

neuroepithelium

55
Q

What cells do neuroepithelial cells make?

A
56
Q

Microglia are the exception as they are not made by the neuroepithelium, what makes microglia?

A
57
Q

What are neural crest cells?

A

Cells of PNS, Autonomic nervous system (neurons and glia)

Non-neuronal cells: e.g. melanocytes, adrenal medulla, meninges, facial bones/cartilage

Located at the dorsal tip of the neural tube and migrate off the neural tube and give rise to a whole host of structures in the embryo

58
Q

What are some neural crest derivatives?

A

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

59
Q

Neural crest forms ___ neurons and ____

A

Neural crest forms PNS neurons and glia

60
Q

The dorsal root ganglia (DRG; spinal ganglia) – sensory component, is formed form what?

A

neural crest

61
Q

The motor component - motor neurons of spinal cord is formed by what?

A

the neural tube

62
Q

What do the elongated spinal nerves form?

A

cauda equina

63
Q

What does the piat mater form at the end of the spinal cord?

A

terminal filum

64
Q

Surface of cerebral hemispheres is initially ______ then you develop ______ (grooves) and ____ (elevations)

A

smooth

sulci

gyri

65
Q

What is the reason for the sulci and gyri developing?

A

space saving - minimises brain volume

Brings together brain regions that would otherwise be far apart – optimises brain wiring and functional organisation

66
Q

What is Lissencephaly?

A

also known as “smooth brain”

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

Many affected children die before age 10

67
Q

What is Polymicrogyria?

A

Excessive number of small gyri

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

68
Q

Other congenital abnormalities (all very rare):

What is Microcephaly?

A

Genetic, drugs, infection (e.g. Zika virus)

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

smaller head than normal

69
Q

Other congenital abnormalities (all very rare):

What is Aegenesis corpus callosum?

A

a complete or partial absence of the corpus callosum

Alone or with other cerebral abnormalities

Effects range from subtle – severe

Cognitive and social difficulties - intellectual impairment, seizures, hypotonia etc

70
Q

Other congenital abnormalities (all very rare):

What is Porencephaly?

A
71
Q

Other congenital abnormalities (all very rare):

What is Schizencephaly?

A

characterized by abnormal slits or clefts in the cerebral hemispheres of the brain

72
Q

What is diastematomyelia (split cord malformation)?

A

a congenital disorder in which a part of the spinal cord is split (sagittal), usually at the level of the upper lumbar vertebra

Spinal cord split longitudinally into 2 parts

Usually associated with vertebral anomalies

Bony or cartilaginous process “fixes” cord in place

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

73
Q

What are causes of intellectual impairment?

A

genetic (e.g. Down’s syndrome)

Radiation

Infectious agents (e.g. rubella, toxoplasmosis, cytomegalovirus)

Birth trauma

postnatal insults (e.g. head injury, infections (e.g. meningitis), lead exposure)

Common cause – maternal alcohol abuse

74
Q

in intellectual impairment there is often ________ gross brain defects

A

no obvious

75
Q

Development of the nervous system begins in week _

A

3

76
Q

Neural tube develops from ______________

A

embryonic ectoderm

77
Q

Neural tube closed by end of _th week. Defects in closure result in ____ (e.g. spina bifida

A

4th

NTDs

78
Q

Neural tube forms _______ and ____ of CNS

A

neurons and glia of CNS

79
Q

•Neural crest cells form neurons and glia of _____ (plus non-neuronal cells)

A

PNS

80
Q

Expansion and bending of neural tube forms _ primary and _ secondary brain vesicles.

A

3

5

81
Q

Lumen of neural tube forms ____________

A

ventricular system

year 2 neuro - Robbie (48 decks)

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