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Conditions + definitions > Neuro embryology > Flashcards

Neuro embryology Flashcards

1
Q

How does the optic cup form?

A

Optic vesicles reach surface ectoderm
>Surface ectoderm cells thicken forming lens placode
Lens placode invaginates causing
>optic vesicle –> optic cup
Optic cup has two layers - ends of cells touch but not joined
Lens vesicle Loses connection with surface ectoderm

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2
Q

What is the choroid fissure, how is it formed?

A

Gap in the inferior wall of the lens vesicle
In between layers
Blood vessels that pass through to optic cup form the fissure

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3
Q

What can go wrong with the choroid fissure?

A

Usually disappears, but if it persists forms a gap called coloboma
Can affect the iris, retina or disc

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4
Q

What does the surface ectoderm of the optic cup form?

A

Eyelids
Conjunctiva
Corneal epithelium

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5
Q

What does the mesenchyme of the optic cup go on to form?

A

Choroid
Stroma of cornea
Sclera
Extraocular muscles

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6
Q

What forms the lens fibres?

A

from epithelium of lens vesicle - later lose their nuclei

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7
Q

When can retinal detachment occur?

A

After trauma - needs a tear in the retina
liquified vitreous humour enters through holes into potential space between 9th + 10th layers of the retina
Leads to a painless loss of vision

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8
Q

Where are the weaknesses of the bony orbit?

A

Medial walls

Floor of orbit

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9
Q

What is the clinical significance of the weaknesses in the bony orbit?

A

Easily fractured leads to herniation into surrounding sinuses
Can lead to tear drop sign - after orbital floor fracture and herniation into maxillary sinus - contents leak into the sinus

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10
Q

What does orbital fat do?

A

Cushions globe

Can however hypertrophy pushing out eye (staring appearance)

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11
Q

What makes up the fibrous layer of the eye?

A

Cornea - anterior 1/6 which is transparent and allows light rays to enter the eyeball
Sclera - opaque posterior gives attachment to muscles moving eyeball

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12
Q

What is the histology of the cornea?

A

Epithelium - stratified squamous non-keratinised

Bowman’s membrane - basement membrane

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13
Q

What is the histology of the stroma?

A

Stroma - regularly arranged collagen - no blood vessels
Descemets layer
Endothelium - single layer
>Has pump that actively keeps out the aqueous humour

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14
Q

How many layers are there to the retina?

A

10 total
9th - Nerve fibre layer
2nd - layer of rods/cones
1st - pigment epithelial layer

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15
Q

What are the four segments of the eyes?

A

Superotemporal
Inferotemporal
Superonasal
Inferonasal

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16
Q

What makes up the vascular layer?

A

Ciliary body - suspens the lens and produces aqueous humour
Iris - controls diameter of pupil - controls light entering eyeball
Choroid - supplies blood to outer retina layers

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17
Q

What is the fovea?

A

area of best site - packed with cones - nerves pushed to side

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18
Q

What is the optic disk?

A

blind spot where the optic nerve meets the eye

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19
Q

What is the lens?

A

transparent crystalline biconvex suspended by ciliary body

Transparent due to avascularity

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20
Q

What are the segments of the eye?

A 
Anterior chamber (AC) in front of iris; posterior chamber (PC) behind iris
Anterior segment in front of lens; posterior behind
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21
Q

What are the functions of the aqueous humour?

A

Aqueous humour - helps maintain intraocular pressure
Produced in ciliary body in space behind iris, in front of lens
Flows through pupil into space behind in front of iris and behind cornea
Reaches angle of anterior chamber where filtered through trabecular meshwork
Enters through schlemms canal
Obstruction - glaucoma

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22
Q

What is the function of the vitreous humour?

A

helps cushions retina

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23
Q

What is the conjunctiva?

A

thin vascular membrane that covers inner surface of eyelids and loops back over sclera.

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24
Q

What are the features of te lacrimal gland/duct?

A

Lacrimal gland situated in lateral orbit.
Innervated by parasympathetic from facial nerve
Duct opens into conjunctival sac
During each blink eyelids sprad tears evenly on surface of cornea
Tears drain through punctae on medial side of each eyelid
Drains into lacrimal sac (sits over lacrimal bone)
Then drains through nasolacrimal duct into inferior meatus of nasal cavity

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25
Q

What are the layers of the tear film?

A

3 layered structure

1) Mucinous layer - 30%
2) Aqueous layer - 69%
3) Oily layer - most superficial

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26
Q

What are the functions of the tear film?

A

Keeps cornea moist , prevents drying
Washes away any particulate foreign bodies
Has antibodies and lysozymes to kill microbes
Smoothes outer surface of cornea providing smooth surface for refraction.
When eyelids open, water evaporates + oily layer becomes closer to mucin layer
When these two layers touch, tear film breaks +stimulates blinking

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27
Q

What are the three primary vesicles of the brain?

A

prosencephalon
Mesencephlon
Rhombencephalon

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28
Q

What happens to the vesicles?

A

Forebrain splits into two: diencephalon + telencephalon
Hindbrain splits into 2
Week 4 3 vesicles, week 5 5 secondary vesicles
Develop into adult brain

29
Q

How do the vesicles form the adult brain?

A

At 25 days the tube is formed
At 40 days the forebrain grows quickly, causing head to fold
Hindbrain curves inwards
At 50 days, forebrain bigger still, midbrain starts to grow
Midbrain still does not grow
100 Days
Forebrain grows bigger, forming cerebral hemispheres
Cerebellum, pons, medulla now identifiable
9 months - adult brain structure

30
Q

What do the secondary vesicles become?

A

Hindbrain - brain stem exc midbrain
Midbrain - midbrain
Diencephalon - diencephalon
Telencephalon - cerebral hemispheres

31
Q

Where do the ventricles arise from?

A

3rd ventricle - diencephalon
Lateral ventricles - telencephalon
4th ventricle - hind brain
Cerebral acqueduct - midbrain

32
Q

When does the CNS start to appear?

A

Beginning of 3rd week

33
Q

How does the CNS start to form?

A

Thickening of ectoderm anterior to the primitive node = NEURAL PLATE.
Edges thicken and move upwards to form the NEURAL FOLDS
Neural folds migrate towards each other and fuse at midline forming the NEURAL TUBE.
Neural tube initially remains open at anterior and posterior ends.

34
Q

How does the neural tube close? What is the closing essential for?

A

Essential for normal development
Processes in cranial + caudal directions - begins day 18
Completed by end of 4th week ~ day 27
Anterior (cranial/rostral) neuropore closes 18 – 20 somite stage (~25 days)
Posterior (caudal) neuropore closes ~ day 27.
Up to 5 closure sites in humans

35
Q

What conditions arise when the neural tube fails to close?

A

Anencephaly
Encephalocoele
Spina bifida

36
Q

What is anencephaly?

A

1:1500 births
Failure of anterior neuropore to close
Brain tissue degenerates due to skull’s failure to form
Incompatible with life

37
Q

What is craniorachischisis?

A

failure of anterior neuropore and rostral neural tube to close

38
Q

What is encephalocele?

A

1:4000 births
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

39
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.

40
Q

What is the occulta form of spina bifida?

A

Most minor
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.

41
Q

What is the cystia form of spina bifida?

A

Protrusion of spinal cord +/- meninges through defect in vertebral arch (1/1000)
Spina bifida with meningocele
Rarest form
Protrusion of meninges and cerebrospinal fluid

42
Q

What is the 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

43
Q

What is the myeloschisis form of spina bifida?

A

Most severe form

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

44
Q

How do you prevent spina bifida?

A

Folic acid supplements

45
Q

What are the risk factors of spina bifida?

A

Genetic predisposition
Nutritional (e.g. too little folate, too much vitamin A)
Environmental (e.g. hyperthermia; taking certain drugs – e.g. sodium valproate)

46
Q

How do you diagnose spina bifida prenatally?

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.
  • Amniocentisis
    >(high levels AFP in amniotic fluid)
  • Ultrasound
    >(Anencephaly from 12 weeks, spina bifida from 16-20 weeks)
47
Q

When and where does the cephalic flexure occur?

A 
End of 3rd week.
Between midbrain (mesencephalon) and hindbrain (rhombencephalon).
48
Q

When and where does the cervical flexure occur?

A

End of 4th week.

Between hindbrain and spinal cord.

49
Q

When and where does the pontine flexure occur?

A

In hindbrain

between metencephalon and myelencephalon

50
Q

What does the prosencephalon go on to form?

A

Diencephalon + telencephalon

51
Q

What does the telencephalon go on to form?

A

Cerebral hemispheres
Hippocampus
Basal ganglia

52
Q

What does the diencephalon go on to form?

A

Pituitary gland
Hypothalamus + thalamus
Pineal gland

53
Q

What does the mesencephalon go on to form?

A

Midbrain

Superior + inferior colliculi

54
Q

What does the rhomboencephalon (hindbrain) go on to form?

A

Metencephalon

Myelencephalon (medulla)

55
Q

What does the Metencephalon go on to form?

A

Cerebellum

Pons

56
Q

When does CSF production start?

A

in 5th week

57
Q

What is hydrocephalus?

A

Accumulation of cerebral spinal fluid resulting in enlarged brain + cranium
Frequently due to blocked cerebral aqueduct
Prevents CSF from lateral + 3rd ventricles passing to 4th

58
Q

What are the causes of hydrocephalus?

A

Genetic
prenatal viral infection
intraventricular haemorrhage
spina bifida cystica

59
Q

How do spinal nerves develop?

A 
Dorsal root ganglia (sensory)
>Neural crest extends via two processes
>Peripheral process to form body
>Central process - dorsal horn of spinal cord (via roots
Motor - from neural tube
60
Q

How does the spinal cord lengthen?

A

3rd month – 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).

61
Q

What forms the autonomic nervous system?

A

Neural crest cells

62
Q

How are sulci + gyri formed?

A

Surface of cerebral hemispheres initially smooth.
Rapid growth results in the development of sulci (grooves) and gyri (elevations).
Pattern becomes more complex as brain enlarges.

63
Q

What is 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.
Many affected children die before age 10.

64
Q

What is polymicrogyria?

A

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

65
Q

What is microcephaly?

A

Small head size
Genetic, drugs, infection
Intellectual impairment, delayed motor functions/speech, hyperactivity, seizures, balance/co-ordination problems etc.

66
Q

What is Aegenesis corpus callosum?

A

Alone or with other cerebral abnormalities
Effects range from subtle – severe
Cognitive and social difficulties
>intellectual impairment, seizures, hypotonia etc

67
Q

What is Schizencephaly?

A

Large clefts/slits in the brian
Genetic, in utero stroke, infection
Paralysis, seizures, intellectual impairment, developmental delay

68
Q

What is porencephaly?

A

CSF filled cysts or cavities
Usually from postnatal stroke or infection
Delayed growth and development, seizures, hypotonia, intellectual impairment

69
Q

What is Distematomyelia?

A

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.

Conditions + definitions (68 decks)

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