Embryology

Question 1

3 Early Brain Vesicles + Derivative of Ea

When does this happen?

Answer 1

• Prosencephalon (forebrain) —> telencephalon (cerebrum) & diencephalon (thalamus and hypothalamus)
• Mesencephalon (midbrain) - UNDIVIDED
• Rhombencephalon (hindbrain) —> metencephalon (pons and cerebellum) & myelencephalon (medulla)

**3 division formed in 1st mo; subdivide in 2nd mo

Question 2

Role of Shh in Neural Patterning

Answer 2

Initiates VENTRAL patterning

Expressed by prechordal mesoderm, notochord and floorplate of neural tube

Question 3

Alar v Basal Plates

Answer 3

Both make up the mantle (post-mitotic cells in that eventually become white and gray matter)

Mantle is divided into dorsal and ventral by sulcus limitans

Dorsal = alar plates (sensory)
ventral = basal plates (motor)

Question 4

Rhombic Lip

Answer 4

B/n 4th ventricle and rhomboencephalon (hindbrain)

Becomes glutamatergic neurons of cerebellum

Question 5

What is the general pattern on neuron generation?

Answer 5

Inside-out; earliest neurons on inside (true of SC and forebrain)

Question 6

Radial v. Tangential Migration

Answer 6

Forebrain

• Radial migration = glutamatergic neurons
• Tangential migration = GABAergic neurons

Question 7

What is the spatial relationship b/n the striatum, thalamus, hypothalamus and internal capsule?

Answer 7

Internal capsule contains ascending and descending fiber tracts (b/n cortex and thalamus and axons to brainstem/SC)

Striatum =deep ganglionic eminences; separated by internal capsule (forms C shape)

• caudate is anterior/superior of capsule
• putamen lies lateral/inferior to capsule

Thalamus and hypothalamus lie deep to internal capsule

Question 8

What causes neural tube defects? (+ 4 Examples)

Answer 8

• Likely due to problems w/ genes involving polarity and regional patterning (Shh) OR folate deficiency b/c folate promotes proliferation during tube closure

1- Anencephaly - neural tube does not close to damage to neural tissue —> no cortex

2- Encephalocele - brain tissue and meninges through skull

3- Myelomeningocele - protrusion of meninges AND SC through defective vertebral column (spina bifida)

4 - Meningocele - ONLY meninges protrudes through column (spina bifida)

Question 9

Holoprosencephaly

Answer 9

-fused or absent forebrain structures; incomplete separation of prosencephalon into 2 hemispheres; can be due to Shh mutation (VENTRAL)

Question 10

Dandy Walker Malformation

Answer 10

• dec or no vermis/enlarged 4th ventricle
• Due to disruption of migration and proliferation at rhombic
  lip
  • Hydrocephalus, movement/coordination/mood/intellect problems

Question 11

Chiari Malformation

Answer 11

• inferior displacement of cerebellar tonsil into spinal canal through foramen magnum
• Headache and lower cranial nerve palsies; hydrocephalus
• Can cause syringomyelia (fluid-filled cavity in SC)

Question 12

Classic (Type I) Lissencephaly

Answer 12

• smooth, thick, disorganized or inverted cortex layers
• Intellectual disability and epilepsy
• Usually due to impairment of neuronal migration b/c microtubule problems
• Type II - cellular overmigration —> subarachnoid space (“cobblestone”)