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Neuro Embryology Flashcards

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1
Q

What does the Ectoderm form?

A

Epidermis

Nervous system

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2
Q

What does the Mesoderm form?

A

Bone
Muscle
Blood cells
etc

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3
Q

What does the endoderm form?

A

Gut
Pharynx
Lungs

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4
Q

What is the hypoblast?

A

Lining of the yolk sac

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5
Q

What does the epiblast form?

A

Generates all 3 germ layers from the primitive streak

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6
Q

How is the neural plate formed?

A

Thickening of ectoderm anterior to the primative node

primitive streak at one end of the trilaminar disc; neural plate at the other

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7
Q

After its formation the neural plates edges thicken and move upwards.
What does this form?

A

Neural folds

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8
Q

What is the groove in the centre of plates between the converging neural folds called?
What does this do?

A

Neural groove

divides the future left and right sides of the embryo

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9
Q

How is the neural tube formed from the neural folds?

A

Neural folds migrate towards echoer and fuse at the midline.

Neural tube zips up

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10
Q

The neural tube remains open at the anterior and posterior ends.
When do these ends close?

A

Anterior (cranial) neuropore
-about day 25

Posterior (caudal) neuropore
-about day 27

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11
Q

Describe the morphological cell changes in neurolation

A

Neural plate forms by notochord signalling ectodermal cells to become columnar

Neural tube starts to fold by cells becoming pyramidal, then triangular (notochord signals)

Fusion is by wound healing mechanisms

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12
Q

How does the ectodermal cells forming the neural tube separate from those that go onto form the epidermis?

A

Once the neural tube is fused this breaks off from the ectoderm and the remaining cell layer will form the epidermis

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13
Q

Describe neural tube closure

A

Essential for normal development and function.

  • Initiated at several points along A-P axis
  • Proceeds in cranial and caudal directions
  • Begins day 18
  • Completed by end of 4th week (around day 27)
  • Up to 5 closure sites in humans
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14
Q

Failure of neural tube to close properly leads to neural tube defects (NTDs).
Name the 3 we need to know about

A

Anencephaly
Encephalocoele
Spina bifida

These are some of the most common congenital abnormalities of the CNS

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15
Q

What is Anencephaly?

A

AKA Exencephaly or Meroencephaly

1:1500 births (4x more common in females

Failure of anterior neuropore to close so telencephalon never develops.
Skull doesnt form over area because brain doesnt form

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16
Q

What is craniorachischisis?

A

Craniorachischisis is the most severe form of neural tube defect in which both the brain and spinal cord remain open to varying degrees. It is a very rare congenital malformation of the central nervous system.

Failure of anterior neuropore and rostral neural tube to close

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17
Q

What is encephaloceole?

A

1:4000 births

Herniation of cerebral tissue through a defect in the skull
Failure in closure of rostal neural tube
Most frequent in occipital region

Variable degree of neurological deficits (depending on size and location)

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18
Q

What are the two forms of encephalocoele?

A

Occipital- encephalocoele

Fronto-nasal encephalocoele

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19
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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20
Q

What is Spina Bifida occulta?

A

Most minor form

failure for embryonic halves of vertebral arch to grow normally and fuse

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

Usually no clinical symptoms

May result in dimple with small tuft of hair

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21
Q

What is spina bifida cystica?

A

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

Three types:

  • Spinal bifida with meningocele
  • Spina bifida with meningomyelocle
  • Myeloschisis
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22
Q

What is spinal bifida with meningocele?

A

Rarest form

Protrusion of meninges and cerebrospinal fluid

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23
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
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24
Q

What is myeloschisis?

A

Most severe form of spina bifida.

Spinal cord in affected area open due to failure of neural folds to fuse.
-> exposed to amniotic fluid as a result causing degeneration

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25
How are Neural tube defects diagnosed?
Prenatal Diagnosis: -Maternal blood screening (Indicated by high level alpha-fetoprotein (AFP) in serum) -Amniocentisis (high levels AFP in amniotic fluid) -Ultrasound (Ancephaly from 12 weeks, spina bifida from 16-20 weeks
26
How can AFP be detected in maternal blood for Neural tube defect diagnosis?
AFP from foetal liver leaks into amniotic fluid then into maternal blood. Best detected at 16-20 weeks
27
What reduces risk of neural tube defects?
Folic acid supplements | 400ug/day causes 50-70% decrease in risk
28
What are the risk factors for neural tube defects?
Genetic predisposition Nutritional (e.g. too little folate, too much vitamin A) Environmental (e.g. hyperthermia, taking certain drugs ( e.g. sodium valproate))
29
Why shouldnt you eat liver when pregnant?
High level of vitamin A
30
What are the 3 primary brain vesicles?
Prosencephalon Mesencephalon Rhombencephalon
31
What does the Prosencephalon divide into?
Telencephalon | Diencephalon
32
What does the Rhombencephalon divide into?
Metencephalon | Myelencephalon
33
What are the 5 secondary brain vesicles?
``` telencephalon diencephalon mesencephalon metencephalon myelencephalon ```
34
When does the cephalic flexure develop? | Where does it develop?
End of 3rd week Between midbrain (mesencephalon) and hindbrain (rhombencephalon)
35
When does the cervicle flexure develop? | Where does it develop?
End of 4th week Between hindbrain and spinal cord
36
When does the pontine flexure develop? | Where does it develop?
5th week In hindbrain (between metencephalon and myelencephalon)
37
What does the telencephalon go onto form?
Cerebral hemispheres Hippocampus Basal ganglia
38
What does the diencephalon go onto form?
Thalamus Hypothalamus Pituitary gland Pineal
39
What does the mesencephalon go onto form?
Midbrain | Superior and inferior colliculi
40
What does the metencephalon go onto form?
Cerebellum | Pons
41
What does the myelencephalon go onto form?
Medulla
42
What does the lumen of the telencephalon form?
Lateral ventricles
43
What does the lumen of the diencephalon form?
3rd ventricle
44
What does the mesencephalon lumen form?
Cerebral aqueduct
45
What does the metencephalon and myelencephalon lumen form?
4th ventricle
46
When does CSF start to be produced?
During 5th week Produced predominantly by choroid plexus in 3rd and 4th lateral ventricles
47
Describe hydrocephalus during development
Hydrocephalus = Accumulation of CSF Results in enlarged brain and cranium Frequently due to blocked aqueduct Prevents CSF from lateral and 3rd ventricle passing to 4th ventricle
48
What are the causes of hydrocephalus during development?
Genetic Prenatal viral infection Intraventricular haemorrhage Spinal bifida cystica
49
What is the cell type of the neural tube?
Initially a single layer of rapidly dividing neuroepithelial cells Then pseudostratified epithelium Divide at ventricular surface
50
Neuroepithelium produces most cells of the CNS. | What cell type does it not produce?
Microglia Mesenchymal cells that migrate into CNS
51
Describe the positional changes of the spinal cord during development
3rd month - extends the entire length of the vertebral column Vertebral column and the fixed dura mater grow more rapidly -> cord at progressively higher levels (L2 or L3, L1 in adults) Initially spinal nerves found at level of origin. Become elongated forming cauda equina Pia mater forms terminal filum
52
What are sympathetic and parasympathetic ganglia formed by?
Neural crest cells
53
How are sulci and gyri formed?
Surface of cerebral hemispheres initially smooth Rapid growth results in the development of sulci and gyri. Pattern becomes more complex as brain enlarges
54
What is Lissencephaly?
"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
55
What is polymicroglia?
Excessive number of small gyri Variable degree of neurological problems (e.g. mental retardation, seizures, motor deficits etc)
56
What is microencephaly?
"Small Brain" Genetic, Drugs, Infection Intellectual impairment, delayed motor functions/speech, hyperactivity seizures, balance and coordination problems etc
57
What is Aegenesis corpus callosum?
Corpus callosum fails to develop. Can occur alone or with other abnormalities Effects range from subtle to severe Cognitive and social difficulties -> intellectual impairment, seizures, hypotonia etc
58
What is Porencephaly?
CSF filled cysts or cavities Usually from postnatal stroke or infection Delayed growth and development, seizures hypotonia, intelectual impairment
59
What is Schizencephaly?
Large clefts or slits in the brain Genetic, in utero stroke, infection Paralysis, Seizures, intellectual impairment, developmental delay
60
What is Diastermatomyelia?
Split cord malformation 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
61
What are the causes of intellectual impairment?
Often no obvious gross brain defects - Genetic (e.g. Down's) - Radiation - Infectious agents (e.g. rubella, toxoplasmosis, CMV) - Birth trauma - Postnatal insults (head injury, infections (e.g. meningitis), lead exposure) MATERNAL ALCOHOL ABUSE -Foetal alcohol syndrome
62
When does the development of the nervous system begin?
Week 3
63
What forms the neurons and glia of CNS?
Neural tube
64
What forms the neurons and glia of the PNS?
neural crest cells | plus non-neuronal cells

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