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Flashcards in Embryology Deck (62):
1

what embryonic layer develops into the nervous system?

ectoderm

2

what does thickening of the ectoderm anterior to the primitive node form?

neural plate

3

the edges of the ectoderm thicken and move upwards in the 3rd week forming what?

neural folds

4

what is formed when the neural folds migrate towards each other and fuse in the midline?

the neural tube

5

when does the anterior neuropore close?

18-20 somite stage (25 days)

6

when does the posterior neuropore close?

day 27

7

describe neural tube closure

> initiated at several pints along the AP axis
> proceeds in cranial and caudal directions
> begins at day 18

8

when is neural tube closure completed?

by the end of the 4th week

9

how may closure sites of the neural tube are in humans?

up to 5

10

name some conditions arising from neural tube defects

> anencephaly
> encephalocoele
> spina bifida

11

what causes meroencephaly?

failure of the anterior neuropore to close so the skull fails to form and the brain tissue degenerates

12

what is craniorachischisis?

failure of the neural tube closure along the entire neuroaxis

13

what causes encephalocoele?

failure in closure of rostral neural tube

14

what is the effect of encephalocoele?

herniation of cerebral tissue through a defect in the skull with a variable degree of neurological deficits

15

what part of the skull is encephalocoele most frequent?

the occipital region

16

in spina bifida where is the closure of the neural tube defective?

the causal end

17

what is the effect of spina bifida?

> affects tissues overlying the spinal cord
> can affect the neural tissue
> severity ranges from minor to major clinical symptoms

18

define spina bifida

non fusion of the vertebral arches

19

describe the cause of spina bifida occulta

failure of the embryonic halfs of vertebral arches to grow normally and fuse.

20

at what vertebral level does spina bifida occulta normally occur?

L5 and L6

21

what are the effects of spina bifida occulta?

> usually no clinical symptoms
> may result in a small tuft of hair

22

what is spina bifida cystica?

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

23

what is spina bifida meningocele?

> rarest form
> protrusion of meninges and cerebral spinal fluid

24

what is spina bifida meningomyelocle?

> nerve roots and/or spinal cord involved
> neurological deficit (sensation loss and paralysis)
> associated with hydrocephalus

25

what is the most severe form of spina bifida cystica?

spina bifida myeloschisis

26

describe spina bifida myeoschisis

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

27

how is spina bifida incidence decreased in the UK

> folic acid supplements
> maternal blood screening
> amniocentisis
> ultrasound

28

describe maternal blood screening in spina bifida

> high levels of alpha-fetoprotein in serum
> best detected at1 16-20 weeks

29

what are the risk factors for spina bifida?

> genetic predisposition
> nutritional (too little foliate, too much vitamin a)
> environmental (hyperthermia, drugs)

30

when does brain vesicle development begin?

with the closure of anterior neuropore

31

name the 3 primary brain vesicles

> prosencephalon (forebrain)
> mesencephalon (midbrain)
> rhombencephaon (hindbrain)

32

name the 5 secondary brain vesicles

> telencephalon
> diencephalon
> mesencephalon
> metencephalon
> myelencephalon

33

where is the cephalic flexure?

between the midbrain (mesencephalon) and the hindbrain (rhombencephalon)

34

where is the cervical flexure?

between the hindbrain and the spinal cord

35

where is the pontine flexure?

in the hindbrain between the metencephalon and myelencephalon

36

what makes up the forebrain (prosencephalon)?

> telencephalon (hemispheres, hippocampus and basal ganglia)
> diencephalon (thalamus, pituitary, diencephalon, pineal)
> mesencephalon (superior and inferior colliculi)

37

what makes up the rhombencephalon- hindbrain?

> metencephalon (cerebellum, pons)
> myelencephalon (medulla)

38

when does CSF begin to form?

during the 5th weeks

39

where is CSF produced?

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

40

what is hydrocephalus?

accumulation of CSF resulting in an enlarged brain and cranium. it is frequently due to a blocked aqueduct preventing CSF from the lateral and 3rd ventricles passing into the 4th ventricle

41

what can cause hydrocephalus?

> genetic
> prenatal viral infection
> intra-ventricular haemorrhage
> spina bifida cystica

42

what cells initially make up the neural tube?

a single layer of neuroepithelial cells

43

what do neuro-epithelial cells differentiate into?

> neurons
> astrocytes
> oligodendrocytes

44

what forms microglia?

mesenchymal cells that migrate into the CSF

45

what two processes does the neural crest extend?

> peripheral process (body)
> central process (dorsal horn of spinal cord)

46

describe the positional changes in the spinal cord

> 3rd month it extends the entire length of the vertebral column
> vertebral column and dura mater grow more rapidly so spinal cord is at progressively higher levels
spinal nerves become elongated forming cauda equina

47

what form the terminal filum?

pia mater

48

what are the sympathetic and parasympathetic ganglia formed by?

neural crest cells

49

describe the formation of the sulci and gyri

brain surface is initially smooth but rapid growth results in the development of sulci and gyri, the pattern becomes more complex as the brain develops

50

what is lissencephaly?

> smooth brain where the gryi and sulci fail to develop
> rare disorder

51

what causes lissencephaly?

defective neural migration

52

what is the result of lissencephaly?

> severe mental impairment
> failure to thrive
> seizures
> abnormal muscle tone

53

what is polymicrogyria?

excessive number of small gyri resulting in a variable degree of neurological problems (mental retardation, seizures, motor deficits)

54

what is the effect of microcephaly?

> intellectual impairment
> delayed motor and speech function
> hyperactivity
> seizures
> balance problems

55

what are the effects of aegenesis corpus callosum?

> cognitive and social difficulties
> intellectual impairment
> seizures
> hypotonia
> can range from subtle to severe

56

what is porencephaly?

CSF filled cysts or cavities from a postnatal stroke or infection

57

what is the effect of porencephaly?

> delayed growth and development
> seizures
> hypotonia
> intellectual impairment

58

what is schizencephaly?

large clefts or slits in the brain due to genetics, in utero stroke or infection

59

what is the effect of schizencephaly?

> paralysis
> seizures
> intellectual impairment
> developmental delay

60

what is diastematomyelia?

where the spinal cord is split longitudinally into 2 pairs and bony/cartilaginous process fixes the cord in place

61

what is the effects of diastematomyelia?

> scoliosis
> weakness of extremities
> hairy patch over lower back
> foot deformities
> loss of sensation

62

what are some causes for intellectual impairment when there is no gross brain defect?

> genetic
> radiation
> infectious agents
> birth trauma
> postnatal insults
> maternal alcohol abuse