Developing Brain

Question 1

Neurulation

Answer 1

(days 18-24)

Question 2

spina bifida or
anencephaly

Answer 2

Incomplete closure of the
neural tube during neurulation (folic acid can help prevent this)

Question 3

After the neural tube has formed, neurogenesis, the formation of
new neuron precursors, begins in the innermost portion of the neural
tube called the

Answer 3

ventricular zone, bordering the central canal (ventricle)

Question 4

Neurogenesis

Answer 4

proliferation of a single layer of cells that line the
neural tube’s central canal (ventricle), the ventricular zone

Question 5

migration disorders can cause

Answer 5

epilepsy, developmental
delay…

Question 6

inside-out pattern

Answer 6

The cerebral cortex forms in inside-out pattern: inner layers
first, then layers are added on top towards the outer surface

Question 7

Are new neurons formed after birth?

Answer 7

The bulk of human neurogenesis occurs prenatally
* In rodents, adult neurogenesis exists and is increased by
learning & exercise, decreased by stress, notably in the
hippocampus
* Some amounts of neurogenesis do occur after birth in
humans, notably in the first ~2y and, in tiny amounts through
~young adulthood

Question 8

As dendrites, synapses, and glia grow more abundant and
complex, brain size, cortical thickness, gray matter volume,
cortical surface area dramatically increase in the first ____ yrs.

Answer 8

~2y
– Brain doubles in volume in first year, 90% of adult size by age 5

Question 9

initial overproduction of dendrites, axons, and synapses,
starts during _____ and continues ___.

Answer 9

the 3rd trimester of prenatal life and continues
after birth (until ~2 years for dendrites, adolescence for
synapses)

Question 10

synaptic pruning

Answer 10

Followed by selective retraction of synapses towards adult
levels

Question 11

Net cortical thinning & grey matter loss occurs from ____ to ____.

Answer 11

from puberty through young adulthood as the brain further matures (e.g.,
synapses get sharply pruned back towards adult levels)
Primary sensory and motor cortex matures earlier
* Attention, executive function, multimodal association areas
mature later

Question 12

Myelination

Answer 12

The brain isn’t fully myelinated at birth
* Myelination starts prenatally, and continues through early
adulthood (going roughly from central to periphery, and from
caudal to rostral)
* Speeds up signal conduction: brain gets faster, more efficient
* DTI indirectly measures myelination of tracts (↑ myelination is
associated with ↓ diffusivity and ↑ fractional anisotropy )