Prenatal Brain Development

Vocabulary flashcards covering the key processes, timing, and structural milestones of prenatal human brain development as presented in MEDSCI 317 Lecture 1.

Neurulation

The initial development of the central nervous system occurring approximately $2\text{--}3$ weeks after conception.

Ectoderm

The embryonic cell layer responsible for forming nervous system structures.

Mesoderm

The embryonic cell layer that develops into musculature and skeletal structures.

Endoderm

The embryonic cell layer that forms internal organs.

Neuroepithelial cells

Precursor cells in the neural plate that rapidly proliferate between $4\text{--}5$ weeks gestation to drive brain growth.

Proliferation rate

The speed of cell creation adjacent to the ventricles, which can reach up to $250,000/\text{min}$.

Neurogenesis

The formation of new neurons, which initiates at approximately $8$ weeks of gestation.

Gliogenesis

The formation of astrocytes and oligodendrocytes, which initiates around $6$ months of gestation.

Active migration

An "inside out" movement over long distances where younger neurons move past older ones, primarily seen in the cerebral cortex.

Passive migration

Movement by cell displacement where the oldest cells end up located farthest away from the proliferative zone, such as in the thalamus or brain stem.

Radial glial cells

Cells that act as "guide wires" or scaffolds for immature neurons to propel themselves toward their final destination.

Tangential migration

A parallel mode of active migration used by GABAergic interneurons migrating from the MGE and LGE into the cortex.

Dendrogenesis

The growth and arborization of dendrites, which acts as the major driver of rapid cortical growth observed in the last trimester.

Growth cone

A highly motile structure at the end of a developing axon that detects chemical guidance cues like Netrins, Slits, Ephrins, and Semaphorins.

Synaptogenesis

The formation of synapses between neurons, occurring at a rate of approximately $40,000$ per second starting around week $28$.

Thalamocortical (TC) pathway

A pathway connecting the thalamus to the cortex to relay sensorimotor information from receptors to the brain.

Subplate (SP)

A transient neuronal layer in fetal life that serves as a "waiting zone" for thalamocortical fibers before they synapse with final targets in Layer 4.

Apoptosis

A tightly regulated, energy-dependent process of programmed cell death that removes $50\text{--}70\text{\%}$ of neurons that fail to compete for neurotrophins.

Fetal Yawning

A behavior appearing between the $10\text{th}$ and $15\text{th}$ week that signals the beginning of sleep stages in the fetal brain.

Vernix and lanugo

Substances that protect the fetus's skin from chapping while in the amniotic fluid during the second trimester.