Embryology II

Question 1

How many neurons and glial cells are there in the brain?

Answer 1

10^12

Question 2

How many cells are in the neurectoderm?

Answer 2

10^5

Question 3

How many synapses are in the brain?

Answer 3

10^15

Question 4

How many miles of axons are in the brain?

Answer 4

10^6

Question 5

Neural cells are generated in ______________.

Answer 5

ventricular zones (areas of the developing brain that are immediately adjacent to a ventricle)

Question 6

Where are the secondary zones of neurogenesis?

Answer 6

• Subventricular zone: gives rise to cells in the olfactory bulb
• External granule layer: gives rise to the granule neurons in the cerebellum (primarily postnatal)
• Dentate gyrus: part of the hippocampus that gives rise to cells involved in learning and memory

Question 7

Describe the differences in migration of ventricular and subventricular cells.

Answer 7

Ventricular: migrates directly to the nearest layer
Subventricular: migrates to the furthest layer

Question 8

Track the movement of the nucleus in a cell dividing in the ventricular zone.

Answer 8

G1: remains halfway between pia and ventricular layer
S: moves up toward the pia
G2: moves back to the halfway point
M: detaches from the pia and shrinks down toward the ventricular layer

Question 9

During mitosis on the ventricular zone, how does division differ between cells that leave the cell cycle and cells that remain in the cell cycle?

Answer 9

Those that exit the cycle will have a horizontal division (in which one cell is closer to the pia) – producing an asymmetric division – and those that remain in the cycle will have a vertical division – resulting in a symmetric division.

Question 10

The __________ gives rise to all the cells of the peripheral nervous system.

Answer 10

neural crest

Question 11

Most of the neural crest cells that migrate through the dorsal pathway become __________.

Answer 11

pigment cells – not neurons

Question 12

The neural crest cells that become PNS neurons migrate __________.

Answer 12

ventrally (that is, ventral to the dermatomes)

Question 13

What receptors on neural crest cells guide migration?

Answer 13

Integrins

Question 14

Which ligands bind to integrins on neural crest cells?

Answer 14

Laminin and fibronectin

Question 15

Olfactory cells arise from the subventricular zone in a feature called the ____________, a type of chain migration.

Answer 15

rostral migratory stream

Question 16

GABA-ergic interneurons arise from __________ migration, from ganglionic eminences.

Answer 16

tangential

Question 17

Neurogenesis begins after what embryonic process finishes?

Answer 17

After the neural tube folds

Question 18

Why do dividing neural cells move during the phases of the cell cycle?

Answer 18

The reason is not known.

Question 19

Most of neurogenesis occurs prenatally, but there are three exceptions. What are they?

Answer 19

1) Cerebellar granule cells
2) Olfactory cells
3) Hippocampus cells

Question 20

The secondary-zone neurogenesis cells also arise from ______________.

Answer 20

ventricular zones; however, they migrate without exiting the cell cycle

Question 21

Division of ventricular cells in a plane parallel to the ventricle surface can lead to unequal protein allocation. This process is thought to play a role in cell differentiation. Which three proteins have demonstrated this effect?

Answer 21

Prospero
Numb
Miranda

Question 22

The first layer of ventricular cells to become postmitotic is the _________ layer (around week 8-9).

Answer 22

preplate

Question 23

The preplate then divides into what four layers (from outermost to innermost)?

Answer 23

Marginal zone, cortical plate, subplate, and intermediate zone

Question 24

Mutations in the filamin A protein can lead to a condition called ___________.

Answer 24

periventricular heterotopia