L3 - Disorders of Neural Development

Question 1

What is a focal lesion?

Answer 1

Circumscribed areas of injury to brain tissue following brain injury.
May occur:
- object penetrates skull and directly injures brain.
- vascular damage (closed head injury)

Question 2

Define: Sporadic

Answer 2

Occurring at irregular intervals or only in a few places.

Question 3

Define: Monogenetic

Answer 3

Having a single source.

Question 4

Define: Oligogenetic

Answer 4

Caused by relatively few genes.

Question 5

Define: Polygenetic

Answer 5

Caused by many different genes, each having only a limited impact on phenotype.

Question 6

Define: Idiopathic

Answer 6

Relating to any disease which arises spontaneously or for which the cause is unknown.

Question 7

Define: Epigenetic

Answer 7

• Study of changes in organism
• caused by modification of gene expression
• rather than alteration of the genetic code itself.

Question 8

Briefly describe neuralation?

Answer 8

1. Neuroectodermal cells -(differentiate)-(thicken)- neural plate.
2. Neural plate -(dorsally bends)-(ends join)- Neural crest
3. Neural tube -(closes)-(disconnects)- from neural crest and will form epidermis
4. Notochord-(degenerates)

Question 9

What will neural crest cells differentiate into?

Answer 9

Cells of peripheral nervous system (neurones and glia)

• sensory ganglia (dorsal root ganglia)
• (symp & parasymp ganglia)
• neural plexuses with specific tissues and organs

Question 10

Brain vesicles from rostral neural tube will contribute to what structure?

Answer 10

Brain CNS.

• Proencephalon - telencephalon (cerebrum) & diencephalon (hypothalamus and optic vesicles)
• Mesencephalon - midbrain
• Rhombencephalon - metencephalon (pons & cerebellum)

Question 11

What happens to the neural tube in adulthood?

Answer 11

Outgrown by skeleton - cord ends at L1 vertebra.
Preserved as
- central grey of cord
- periaqueductal grey of midbrain

Question 12

What is a radial glial cell?

• Where do they arise from?
• Role?

Answer 12

• Arise during expansion of neural tube.
• Bi-polar progenitor cells.
• Responsible for producing all neurones in cerebral cortex.
• Newborn neurones use radial glia as scaffolds
• traveling along radial glial fibers to reach final destination.

Question 13

How does the neural tube rapidly develop?

Answer 13

Acquires regional distinctions via inductive cues.

• Retinoic acid and sonic hedgehog (notochord) induces transcription factors
• result in generation of motor neurones and oligodenrocytes from VENTRAL neural tube.
• Local signaling by Wnt and BMP in DORSAL regions generates neural crest and sensory neuron precursors.

Question 14

What is BMP4?

Answer 14

Bone Morphogenetic Protein 4.

• protein coding gene
• part of transforming growth factor-beta family
• found in early embryonic development
• involved in bone and cartilage development.

Question 15

What is the role of BMP4 in humans embryonic development?

Where is it secreted from?

Answer 15

• Critical signalling molecule required for early differentiation of embryo.
• secreted from dorsal part of notochord.
• acts with sonic hedgehog (ventral part of notochord)
• establishes dorsal and ventral axis

Question 16

What is chordin?

Answer 16

• Bone morphogenetic protein antagonist

- Dorsalizes developing embryo by binding ventralizing TGF-beta proteins such as BMPs

Question 17

What is noggin?

Answer 17

Inhibitor of BMPs
Promotes somite patterning in developing embryo.
Released from notochord.
Causes formation of head and other dorsal structures.

Question 18

Describe pruning?

Answer 18

• Selective degeneration of axons.
• Neurone axons will be pruned via apoptosis.
• Casp6 - mediator of axon degeneration, activated following nerve growth factor (NGF) deprivation.

Question 19

What is neurofibromastosis type 1?

Answer 19

• Genetic condition causing tumours to grown along nerves.
• Autosomal dominant.
• Caused by mutation in neurofibromin gene as part of the RAS system.

Question 20

What are some features of neurofibromastosis type 1?

Answer 20

Ectoderm 
- dermal neurofibromata 
- Cafe-au-lait spots 
- Axillary freckling 
Neural tube effects
- glial cell tumour
Neural crest effects 
- schwann cell tumours

Question 21

What is dermal neurofibromata?

Answer 21

• non cancerous
• tumours growing from small nerves in skin
• appear as small lumps during puberty

Question 22

Describe disorders related to development, neural tube defects?

Answer 22

• Rostral/ caudal end of neural tube (neural pores) may fail to close.
• May lead to neural tube defects (spinal bifida)

Question 23

What is anencephaly?

Answer 23

Failure of brain to develop.

Neural tube closed but membrane around it may not have.

Question 24

Describe the severity of spina bifida occulta?

Answer 24

• mild / commoner form
• discovered on X-rays
• most never become aware they have it

Question 25

Describe spina bifida cystica? (4)

Answer 25

examples:

• Meningocoele
• Myelocoele
• Encephalocoele
• Encephalomyelocoele

Question 26

Key role of folic acid?

Answer 26

Co-factor in cell division.

Question 27

Describe meningocele?

Answer 27

• coverings of spinal cord (meninges) pass back through opening in spine to form a cyst like swelling.

Question 28

Describe myelomeningocele?

Answer 28

• spinal cord enclosed in cyst.

- most serious type of spina bifida

Question 29

Define Paraparesis

Answer 29

Partial paralysis of lower limbs.

Question 30

Define: Paraplegia

Answer 30

Paraplegia - impairment in motor or sensory function of the lower extremities

Question 31

What are some effects of lost neural function?

Answer 31

• Limb deformity
• Urine infection risk
• Hydrocephalus
• Immobility
• Obstetric complications

Question 32

What is cortical heterotropia?

Answer 32

Cortical cells (grey matter) are present in inappropriate locations in brain.

• almost always cause epileptic seizures
• may or may not be associated with learning disability

Question 33

What is microcephaly?

Answer 33

babies with smaller heads.

Question 34

What is Chiari malformation?

Answer 34

Brain tissue extends into spinal canal.

Relatively mild abnormalities of skull base may cause altered flow of CSF.

Question 35

What is Syringomyelia?

symptoms?

Answer 35

Generic term, cyst or cavity forms within the spinal cord.
- cyst can expand, elongate over time, destroying the spinal cord.

Symptoms: loss of feeling, paralysis, weakness, stiffness in back, shoulders and extremities

Question 36

What is infant Hypoxic Ischemic Encephalopathy?

Answer 36

Type of brain damage that occurs when an infant’s brain doesn’t receive enough oxygen and blood.

Question 37

What is Strabismus?

Answer 37

Condition where patient cannot align both eyes simultaneously under normal conditions.

Question 38

What is Duane’s syndrome?

Answer 38

• Limitation of horizontal eye movement.
• Caused by weakness in lateral rectus.
• Inability to move eye inward toward the nose (adduction), outward toward ear (abduction) or in both directions

Question 39

What may occur during adduction in a person with Duane’s syndrome?

Answer 39

Eyeball pulls in and eye opening (palpable fissure) narrows.

Question 40

Another word for lazy eye…

Answer 40

Amblyopia

- when vision in one eye is reduced as eye and brain are not working together properly.

Question 41

Give an example of a treatment which may help in a patient with Strabismus?

Answer 41

Occlusion treatment.
- Covering the good eye allows brain to become receptive to connections from weak eye, previously suppressed if any discrepancy of ocular axes.