VAN 211: Veterinary Histology and Embryology (2+2)

Nervous system-CNS

NERVOUS SYSTEM

• The primordium of the nervous system is one of the first structures to appear in the embryo. A thickening of the dorsal ectoderm called neural plate develops first along the mid dorsal line of the embryo. By unequal growth the neural plate is folded into a neural groove bounded by neural fold.
• The groove deepens and the folds meet above thus forming a neural tube. At this point of formation of a neural tube, some of the neural plate cells escape into the space between the neural tube and surface ectoderm.
• The escaped cells form two ridges parallel to the dorsal half of the neural tube called neural crest.

Central Nervous System

• The cranial end of the neural tube presents two constrictions separating three brain vesicles. An expansion at the most rostral end of the neural tube forms the prosencephalon. An evagination growing outwards from each side of the prosencephalon is the optic vesicles. Caudal to this, two enlarged regions are formed, the mesencephalon and rhombencephalon.
• The rostral end of the neural tube begins to expand bilaterally marking the division of prosencephalon into telencephalon and diencephalons. The paired telencephalic vesicles will develop into the cerebral hemispheres. The diencephalons is located in the midline and connected to the expanding optic vesicles. The thalamus, hypothalamus and neural component of pituitary gland develop in this part of the brain.
• The rhombencephalon divides into rostral metencephalon and caudal myelencephalon. The metencephalon gives rise to cerebellum dorsally and pons ventrally. The myclencephalon forms the medulla oblongata. The rest of the neural tube develops as spinal cord.
• Within each telencephalic vesicle lateral ventricles are formed. The third ventricle is developed in the diencephalons. The cavity of the midbrain vesicle remains as cerebral aqueduct. The lumen of the rest of the neural tube forms the central canal of the spinal cord.