Brain flexures

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6 stages of CNS maturation

• As the primary brain vesicles develop, the brain flexes (bends) to form:
• Mesencephalic flexure (or cephalic flexure)
• In the region of the midbrain
• The mesencephalon and the rhombencephalon are separated by a constriction called the isthmus rhombencephalii
• Cervical flexure:
• Junction of the hindbrain and the spinal cord
• Compensatory pontine flexure:
• Forms between the cephalic and cervical flexures.
• At the middle of the rhombencephalon,
• Dividing it into the metencephalon and myelencephalon
• Bending at pontine flexure causes the 4th ventricle to look like a look like a rhomboid shape.
• Telencephalic flexure
• Forms the sylvian fissure
• both the dorsal (frontal) and ventral (temporal) lips of the fissure are derived from the ventral part of the primitive telencephalon (ORANGE)
• Ventrodorsal genetic gradients in the vertical axis can affect both lips, as in schizencephaly.
• The insula is an infolding of tissue secondary to bending of the hemisphere.
• Original posterior pole of the primitive telencephalic hemisphere becomes the temporal, not the occipital pole of the mature brain.
• The occipital horn of the lateral ventricle is a new recess that forms after folding of the telencephalon.