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Medicine Year 2 > HNN Topic 16 - Development of the CNS > Flashcards

HNN Topic 16 - Development of the CNS Flashcards

1
Q

How is SHH involved in eye development?

A
  • Needed for forebrain development - separates L and R side
  • Early in eye development needed to separate the eye field to give two eyes
  • Also has role in creating optic stalk (with PAX 2/6)
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2
Q

What is the result of disruption of migration of neural crest cells?

A
  • Treacher-Collins Syndrome
    • Under development of zygote bone and ears
    • Mutation of TCOF1 gene, retinoic acid exposure?
  • Di George Syndrome
    • 22q11.2 deletion syndrome
    • Cleft palate, cardiac abnormalities, abnormal facies, thymic aplasia
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3
Q

Describe the structure of the brain during week 5 of developement

A
  • Prosencephalon - telencephalon + diencephalon
    • Telecephalon - cerebrum
    • Diencephalon - eye cup + thalamus, hypothalamus + epithalamus
  • Mesencephalon - midbrain
  • Rhombencephalon - metencephalon + myelecephalon
    • Metencephalon - pons + cerebellum
    • Myelencephalon - medulla oblongata
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4
Q

From where do neural crest cells originate?

A
  • Tissue at top of neural folds becomes pinched off - neural crest tissue
  • Neural crest cells at lateral border dissociate, change from epithelial to mesenchymal
  • Leave neuroectoderm by active migration and displace, enter underlying mesoderm
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5
Q

What is the first step in development of the neural tube?

A

Development of the notochord

  • Tube extends from primitive streak in opposite direction
  • Tube first forms axial process, then notochord process, then notochord
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6
Q

What causes congenital cataracts?

A

Genetic causes, rubella infection between 4-7 weeks

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7
Q

What is the inductory function of the optic vesicles?

A

In contact with the surface ectoderm, induce changes necessary for lens formation

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8
Q

How do neural tube defects occur?

A
  • Result of failure of/incomplete closure of neural tube
    • Anterior neuropore - anencephaly
    • Posterior neuropore - spina bifida
    • Most common in lumbosacral region
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9
Q

What is the inductive role of the notochord?

A

Notochord induces overlying ectoderm to thicken and form the neural plate

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10
Q

What forms the iris and ciliary body?

A

At rim of optic cup, both retinal layers form iris and ciliary body

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11
Q

Describe the structure of the brain at week 3 of development

A
  • 3 primary brain vesicles
    • Forebrain - presencephalon
    • Midbrain - mesencephalon
    • Hindbrain - rhombencephalon
  • Uneven growth produces folds/flexures
  • Midbrain - cephalic flexure, head fold, convex dorsally
  • Pontine flexure - convex laterally
  • Cervical flexure at hindbrain/spinal cord junction, temporary (5-7 weeks), convex dorsally
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12
Q

Describe the growth of spinal nerves

A
  • Motor axons from basal plate (ventral horn) - week 4
  • Neurons in dorsal root ganglia extend towards dorsal horn and periphery
  • Dorsal root fibres carry sensory innervation, ventral root fibres carry motor
  • Spinal nerves - sensory + motor
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13
Q

When does the developing eye first appear?

A

At 22 days as pair of shallow grooves - outgrowths of the diencephalon called optic vesicles

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14
Q

List the genes resposible for molecular regulation of eye development

A
  1. PAX 2/6
  2. Sonic hedgehog
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15
Q

When do the cerebral hemispheres divide?

A

Week 8

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16
Q

When does the developing CNS first appear? What is the first sign of its development?

A

Appears at week 3, first sign = thickening of ectoderm in primitive streak

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17
Q

What are the consequences of myelomeningocoele spina bifida?

A
  • Nerves at level of lesion are damaged/don’t form properly
  • Loss of sensation/paralysis below level of defect
  • More cranial = more serious
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18
Q

Describe the closure of the neural tube

A
  • Begins in cervical region, moves cephalic and caudally
  • Open ends form anterior and posterior neuropores - connect with overlying amniotic cavity
  • Closure in week 4 - anterior neuropore by day 25, posterior by day 27
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19
Q

Describe the folding of the neural plate

A
  • Lengthens and lateral edges elevate (neural folds), midline depresses (neural groove)
  • Folds join at midline - forms neural tube
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20
Q

Describe the formation of the eyelids

A
  • Folds of ectoderm with mesenchyme between that grow over the cornea
  • Fuse, enclosing a conjunctiva/sack anterior to cornea
  • Inner layer of ectoderm becomes conjunctiva, fuses with cornea
  • Lacrimal glands form as ectodermal buds from the upper conjunctival sac into the surrounding mesoderm
  • Eyelids separate again between 5th and &th months in utero
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21
Q

Describe the types of spina bifida

A
  • Occulta - mild, tuft of hair in skin over defect
  • Meningocoele - meninges protrude though gap in vertebrae, least common
  • Myelomeningocoele - flattened, plate-like mass of nervous tissue with no overlying protective layer
22
Q

Where does the sulcus limitans extend to?

A

Mesencephalon

23
Q

Define gastrulation

A

Process by which 3 germ layers are formed - ectoderm, mesoderm, endoderm

24
Q

Describe the formation of the lens

A
  • Initially hollow, derived from surface ectoderm
  • Cells of lens vesicle elongate anteriorly to form long lens fibres - adult fibres contrain no organelles or nuclei
  • Arrange in a laminar pattern to form a transparent lens
25
Q

What is the initial event in neuralation?

A

Cells of neural plate make up neuroectoderm

26
Q

Describe the shape of the neural tube

A

Wider at cranial end, narrower at caudal end

27
Q

List types of eye abnormalities

A
  • Congenital cataracts
  • Microphthalmia
  • Anophthalmia
  • Aniridia
  • Cylopia
28
Q

What is microphthalmia and what causes it?

A

Eye too small, genetic abnormalities/intrauterine infections/foetal alcohol syndrome

29
Q

From where does the choroid plexus develop?

A

Develops where pia mater and ependyma come into direct contact e.g. roof of fourth ventricle

30
Q

Describe the formation of the optic nerve

A
  1. Optic cup connected to brain by optic stalk hyaloid vessels in choroidal fissure
  2. Inner and outer layer fuse. Cavity of stalk disappears. Inner layer cells provide a network of neuroglia that support the optic nerve fibres
  3. Optic stalk forms optic nerve. Hyaloid artery and vein become central artery and vein of the retina.
31
Q

Describe the formation of the structure of the spinal cord

A
  • Longitudinal groove = sulcus limitans, divides dorsal and ventral horns
  • Roof plate (dorsal) and floor plate (ventral)
    • No neuroblasts
    • Pathways for nerve fibres to cross from one side to the other
  • Eventually can see
    • Dorsal, ventral and intermediate horns (sympathetic portion of ANS neurons, only in thoracic and upper lumbar segments)
    • Ventral fissure, dorsal median septum
32
Q

How can neural tube defects be prevented?

A

Folic acid prior to conception and in early stages of pregnancy reduces risk

33
Q

Describe the path of neural crest cells

A
  • Cells from trunk go through holes in basal ganglia, form melanocytes + hair follicles
  • Also go to dorsal root ganglion etc - migrate ventrally though anterior somite
  • Migrate from cranial end before neural tube has fully closed - contribute to craniofacial skeleton + neurons for cranial ganglia, glia and melanocytes
34
Q

Which germ layer is the notochord derived from?

A

Mesoderm

35
Q

Describe the signalling which occurs to regulate neuralation

A
  • Up-regulation of FGF, inhibition of BMP-4 causes induction of neural plate
  • Chordin and noggin help inhibition of BMP-4
  • Neural plate switches from E-cadherin to N-cadherin expression
36
Q

Describe the structure of the optic cup

A
  • Bilaminar structure
    • Outer layer forms pigmented layer of retina
    • Inner layer forms nervous layer of retina
  • Space between layers disappears as axons grow from optic nerve
  • Potential weakness remains - detached retina after blow to head
37
Q

How do the neural plate cells change during neuralation?

A

Become more columnar

38
Q

When is development of the eye complete?

A

Week 10

39
Q

Which tissues are derived from ectoderm?

A

CNS, PNS, sensory epithelium of ear/nose/eye, epidermis, hair + nails, subcutaneous, mammary/pituitary gland, enamel of teeth

40
Q

What is the difference between E-cadherin and N-cadherin?

A

E is epithelial, N is mesenchymal (migratory - prevents fusion of neural tube and ectoderm)

41
Q

How does the structure of the lens begin?

A
  • Starts as placode, cells become columnar + invaginate, pushes against optic vesicle
  • ‘Double-walled cups’
42
Q

How is PAX 6 involved in development of the eye?

A
  • Key regulatory molecule
  • Expressed in anterior neural plate before neuralation begins
  • Correct expression required to control inductive events that form the lens and cornea
43
Q

Describe the differentiation of the spinal cord

A
  • Neuroepithelial cells (thick pseudostratified epithelium) extend over entire neural tube, give rise to neuroblasts
  • Neuroblasts form mantle layer - later forms grey matter
  • Outer marginal layer contains nerve fibres emerging from neuroblasts in the mantle layer - becomes myelinated white matter
  • Thickening of dorsal and ventral aspects
    • Dorsal - alar plate (sensory)
    • Ventral - basal plate (motor)
44
Q

What determines the folding of the neural plate?

A

Depends on a number of factors:

  • Intrinsic factors - cytoskeleton, stage of cell cycle
  • Extrinsic factors - adhesion points e.g. within notochord, surface ectoderm
45
Q

What are the meninges derived from?

A
  • Mesenchymal and neural crest cells
  • Day 20-35, cells migrate from around neural tube, form external layer (dura mater) and internal layer (pia and arachnoid mater)
46
Q

What is anophthalmia and what causes it?

A

Absence of eye - genetic/infection

47
Q

Describe the development of the eyeball

A
  • Mesenchyme around optic cup condenses to form layers of eyeball - choroid and sclera
  • Anterior cornea becomes transparent
  • Spaces develop in mesenchyme between cornea + lens - anterior chamber
  • Fibrous tissue with a gelatinous substance (vitreous humour) fills the gap between the lens and retina - vitreous body, posterior chamber
48
Q

What is aniridia and what causes it?

A

Absence of iris, mutation in PAX 6

49
Q

Describe the blood supply to the developing eye

A
  • Grooves arise on ventral surface of the optic cup forming the choroidal fissure
  • Branch of ophthalmic artery (hyaloid artery) - passes along the choroidal fissure to supply the lens and developing retina
50
Q

What is cylopia and what causes it?

A

Single eye, failure of prosencephalon to divide orbits or eye - mutation in SHH gene

51
Q

What is a common complication of spina bifida?

A

Hydrocephalus:

  • Especially in spina bifida cystica
  • CSF builds up due to obstruction of the foramen magnum by the cerebellum
  • Large head
  • Raised ICP - compression of brain
  • Drain fluid into abdomen using shunt to relieve pressure
52
Q

What do neural crest cells give rise to?

A

Ganglia, Schwann cells, adrenal medulla, melanocytes, connective tissue in head

Medicine Year 2 (41 decks)

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