Development and Differentiation of the Neural Tube

The 3 Part Stage

As the neural tube develops, the anterior portion will become the brain while the posterior postion will become the spinal cord. In the diagram, three bulgesof the brain region of the neural tube are shown. The most anterior part of the developing brain is called the prosencephalon (forebrain). The middle portion is called the mesencephalon (midbrain). The most posterior part is the rhombencepahlon. As development continues, the prosencephalon will divide into two parts - the telencephalon and the diencephalon. The rhombencephalon will also divide into two parts - the metencephalon and the myelencephalon.

The 5 Part Stage

Here we see the neural tube a little later in the chick's development. This stage is called the "five part" stage, as the neurocoele is divided into five portions along its midline. The three part origin is still obvious at this time, with the prosencephalon having divided into the telencephalon and the diencephalon, and the rhombencephalon having divided into the metencephalon and the myelencephalon. Due to this further differentiation of the neural tube, it is now possible to see where the various ventricles (expanded portions of the neurocoele) and the future constricted portions of the neurocoele will form.

The 50 Hour Stage

In this diagram, we see the chick at approximately 50 hours of incubation. Due to the twisting of the cranial aspect of the chick, we see the brain region of the neural tube from a lateral view (the previous two diagrams were dorsal views). The five parts continue to develop, but have not changed their basic shape substantially since the last diagram, despite the flexions, twisting and development of the optic vesicle as an evagination from the diencephalon.

The chart below illustrates the development of the subdivisions of the embryonic brain and the adult derivatives. The chart has been colour coded to match the colours representing the subdivisions of the brain in the diagrams of neural tube development above. The gradient effect seen with "4^th ventricle" indicates that it is a part of both the subdivisions. The differentiation of the four initial areas of the neural tube proceeds from left to right across the chart. The cavities listed in the right hand column show what remains of the neurocoele in the fully developed animal. The ventricles are expanded portions of the neurocoele.

Subdivisions and Derivatives of the Neural Tube
	Primary Divisions	Subdivisions	Main Constituent Parts of Adult	Cavities
	Prosencephalon	Telencephalon	- Olfactory lobes - Cerebral hemispheres	- Lateral ventricles - Rostral portion of the 3rd ventricle
		Diencephalon	- Epithalamus (epiphysis) - Thalamus - Hypothalamus - Infundibulum	- Most of the 3rd ventricle
	Mesencephalon	Mesencephalon	- Optic lobes (fish, reptiles, birds) - Colliculi/Corpora quadrigemini (mammals) - Cerebral peduncle	- Cerebral aqueduct
	Rhombencephalon	Metencephalon	- Cerebellum - Pons (mammals)	- 4th ventricle
		Myelencephalon	- Medulla oblongata
	Spinal cord	Spinal cord	- Spinal cord	- Central canal

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Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Page revised: May 2012