Development of nervous system Assist Prof. Naziha Sultan Ahmed The dura mater and arachnoid (layers ofmeninges) , still extend to the middle of the sacral canal. The spinal meninges contain a pool of cerebrospinal fluid (CSF) which can be tapped for diagnostic purposes. In the adult the spinal cord usually extends to the level of the first lumbar vertebra , Hence , when one is performing spinal lumbar punctures to obtain CSF , the needle usually inserted between the vertebral arches of third and fourth lumbar vertebrae to avoid damage to the spinal cord. The spinal cord has two enlargments : 1-Cervical enlargement ,from which brachial plexus arises. 2-Lumbosacral enlargement , from which the lumbosacral plexus arises. Derivatives of the layers of neural tube : =The ependymal layer cells giverise to neuroblasts and glioblasts , dorsal median septum , ventral median fissure and central canal . =The mantle layer cells giverise to dorsal gray horn , ventral gray horn , dorsal gray commissure , ventral gray commissure. =The marginal layer cells giverise to dorsal funiculus (found between septum and root) and lateral funiculus(found between the two roots). Development of the brain: Before the neural tube forms , the neural plate is expanded rostrally where the brain will develop . As the neural tube forms and rostral neuropore closes , the thickened neural folds rise to form three primary brain vesicles ; forebrain (prosencephalon) vesicle , midbrain (mesencephalon) , hindbrain (rhombencephalon). ve 2-Midbrain vesicle (Mesencephalon) Midbrain 3-Hindbrain vesicle Metencephalon Pons , cerebellum & vermis (Rhombencephalon) Myelencephalon Medulla oblongata The development of the head fold in 4th week produces a cervical flexure in the neural tube near the junction of the hindbrain and future spinal cord . As the brain vesicle enlarge , two other flexures form ; midbrain flexure (flexure) which convex dorsally in the region , and the pontine flexure which is convex ventrally in the hindbrain region . .