1: Morphogenesis of the Brain Flashcards
*What are the primary and secondary brain vesicles? (3 primary, 5 secondary)
Primary vesicles: [caudal to rostral]
- Rhombencephalic vesicle - level of brainstem
- Mesencephalic vesicle - level of midbrain
- Prosencephalic vesicle - most rostral
Secondary vesicles: [caudal to rostral]
- Myelencephalon (from rhombencephalic)
- Metencephalon (from rhombencephalic)
- Mesencephalon (from mesencephalic)
- Diencephalon (from prosencephalic)
- Has optic vesicles, which -> retinas - Telencephalon (from prosencephalic)
*What does each secondary vesicle become in the adult?
Metencephalon and myelencephalon -> 4th ventricle
Mesencephalon -> cerebral aqueduct
Diencephalon -> 3rd ventricle
Telencephalon -> lateral ventricles
Cerebellum grows from lateral parts of metencephalon
*What are the primary bends in the neural tube? What do they separate? (2)
Cervical flexure: separates developing spinal cord and brainstem
Cephalic flexure: at level of midbrain
*What are the alar and basal plates? How are these organized in the spinal cord and brain?
Alar plate -> dorsal horn; involved in sensory processing
-Becomes lateral in brainstem (sensory = lateral)
Basal plate -> ventral horn; contains motor neurons
-Becomes medial in brainstem (motor = medial)
*What are the layers of the developing neural tube? What happens in each?
Ventricular zone: where everything starts out
Mantle zone: where post-mitotic cells migrate to
-Send out axons to periphery -> marginal zone
Mantle zone = gray matter, marginal zone = white matter
While the neural tube is expanding, what are the cells of the neural tube doing?
Rapidly dividing!
Maintain connection with lumen of neural tube and pial surface
Bounce back and forth between the pial surface (S phase) and the neural tube lumen surface (M phase of mitosis)
*What causes a “bouncing” neuroblast to stop dividing?
Neuroblasts have notch-1 concentrated in apical portion and numb concentrated in basal portion
Mitosis along pole -> cells keep dividing (have notch and numb)
Mitosis along equator -> one cell has notch I (no numb) -> stops dividing -> migrates to pial surface -> forms mantle zone
-Other cell (with numb) makes notch, keeps dividing
*What factors regulate whether a cell will be a neuron or glial cell? Describe the concept of lateral inhibition.
Notch and delta (another surface marker) are mutually inhibitory, in delicate balance
If balance -> more notch, cell -> glioblast
If balance -> more delta, little notch, activated bHLH genes, cell -> neuroblast
Adjacent cells affected by neighbors (LATERAL INHIBITION): one cell -> neuron, adjacent -> glia and so on (ensure balanced production)
*What layer develops first in the cortex? Which layer is second? (continue)
This is INSIDE OUT cortical development
1st: Layer I, part of the marginal zone
2nd: Layer VI, follows radial glia to layer I and stops below it
3rd: Layer V, follows radial glia to layer I and stops below it, displacing layer VI
4th: Layer IV (same)
5th: Layer III (same)
6th: Layer II (same)
What factor is critical for normal migration? What cells secrete it?
Reelin
From Cajal-Retzius cells
*What are radial glia and what do they do?
Radial glia: glial cells that establish connection from the ventricular surface all the way to the pial surface
Neuroblasts crawl along them to migrate up to the pial surface
*What is formed by the neural crest cells? (4 neuronal, 3 non-neural)
Neuronal things (4): all elements of PNS except somatic/preganglionic autonomic motor axons
- DRG, sensory nerve fibers
- Ganglia of cranial nerves
- Autonomic ganglia
- Adrenal medulla
Non-neural things (3)
- Schwann cells, satellite cells
- Leptomeninges (pia/arachnoid)
- Bone and CT of face and most of the skull
*What factors determine if a neural tube will develop from ectoderm?
Neural tube development induced by INHIBITION of bone morphogenic proteins (BMPs) by presence of noggin and chordin from notochord
Normally, BMP secreted by ectoderm, prevents ectoderm from -> neuroectoderm
Noggin and cordin from notochord bind BMP, block its effect on region to become neural tube
What do all factors that differentiate portions of the nervous system from one another have in common?
All affect nuclear transcription
*What factors differentiate ventral from dorsal part of the neural tube?
Sonic hedgehog (Shh) ventrally (from notochord and then from floorplate) TGF betas dorsally (BMP, dorsalin, retinoic acid, noggin)
Shh most important!
