1.4 Developmental Biology Background
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Fig. 1.4 Neurulation. The neural plate invaginates to create the neural tube. Lateral extension of
adjacent epidermis helps close the tube (center). From Wikimedia Commons
Fig. 1.5 Early brain development. Constrictions divide the brain tube into vesicles. Adapted from
Gilbert (2010)
addition, the telencephalon expands to create the primitive cerebral hemispheres
(Fig. 1.5).
The brain tube is composed of neuroepithelial cells that divide to create neurons,
as well as glial cells. As neurons mature, they extend axons and dendrites. Axons
carry outgoing electrical impulses to other neurons, while dendrites transmit
incoming impulses from other neurons. Glial cells provide structural and metabolic
support for the neurons.
As the hemispheres grow and develop, their walls thicken into a layered structure
surrounding fluid-filled ventricles. Neurons divide near the ventricles and migrate
along radial glial fibers toward the outer surface of the brain, where they form the
cerebral cortex. The cortex is composed mostly of cell bodies and dendrites (gray
matter), while the subcortical layers consist mainly of glia and axons (white matter),
which connect different regions of the cortex.
In most large mammals, the cortex eventually folds into a convoluted shape
consisting of gyri (outward folds) and sulci (inward folds). Cortical folding, which
occurs during the third trimester in humans (Fig. 1.6), greatly increases the surface
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Fig. 1.4 Neurulation. The neural plate invaginates to create the neural tube. Lateral extension of
adjacent epidermis helps close the tube (center). From Wikimedia Commons
Fig. 1.5 Early brain development. Constrictions divide the brain tube into vesicles. Adapted from
Gilbert (2010)
addition, the telencephalon expands to create the primitive cerebral hemispheres
(Fig. 1.5).
The brain tube is composed of neuroepithelial cells that divide to create neurons,
as well as glial cells. As neurons mature, they extend axons and dendrites. Axons
carry outgoing electrical impulses to other neurons, while dendrites transmit
incoming impulses from other neurons. Glial cells provide structural and metabolic
support for the neurons.
As the hemispheres grow and develop, their walls thicken into a layered structure
surrounding fluid-filled ventricles. Neurons divide near the ventricles and migrate
along radial glial fibers toward the outer surface of the brain, where they form the
cerebral cortex. The cortex is composed mostly of cell bodies and dendrites (gray
matter), while the subcortical layers consist mainly of glia and axons (white matter),
which connect different regions of the cortex.
In most large mammals, the cortex eventually folds into a convoluted shape
consisting of gyri (outward folds) and sulci (inward folds). Cortical folding, which
occurs during the third trimester in humans (Fig. 1.6), greatly increases the surface