Primary Brain Vesicles

Constrictions in the neural tube appear to mark off the three primary brain vesicles

–Prosencephalon

•(forebrain)

–Mesencephalon

•(midbrain)

–Rhombencephalon

•(hindbrain)

The remainder of the neural tube becomes the spinal cord

Secondary Brain Vesicles

By the fifth week, the five brain regions of the secondary brain vesicles are evident

The forebrain has divided

–Telencephalon

–Diencephalon

The midbrain remains undivided

The hindbrain has constricted to form

–Metencephalon

–Myelencephalon

Secondary Brain Vesicles

Each of the five secondary brain vesicles develops rapidly to produce the major structures of the adult brain

The greatest change occurs in the telencephalon which sprouts two large swellings which project anteriorly

These paired expansions become the cerebral hemispheres known collectively as the cerebrum

Hemispheres house ventricles

Secondary Brain Vesicles

Various areas of the diencephalon specialize to form

– Hypothalamus

– Thalamus

– Epithalamus

Secondary Brain Vesicles

The mesencephalon develops into

–Midbrain

–Brain stem

Secondary Brain Vesicles

Various areas of the Metencephalon specialize to form

–Brain stem

–Pons

–Cerebellum

Secondary Brain Vesicles

Various areas of the Myelencephalon specialize to form

–Brain stem

–Medulla oblongata

All the midbrain and hindbrain structures, with the exception of the cerebellum, form portions of the brain stem

Development of Flexures

During this period of rapid brain growth change is also occurring in the relative position of its parts

Because the brain’s growth is restricted by the skull, midbrain and cervical flexures develop by the fifth week which bend the forebrain toward the brain stem

Effects of Space Restriction

A second consequence of restricted space is that the cerebral hemispheres are forced to take a horseshoe shaped course posteriorly and laterally

Development of the cerebral hemispheres at 13 weeks