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Development of the Nervous system

zygote forms and divides in two - further division is contineous and there is little increase in size until DAY 7  when implantation occurs.

By DAY 15 structures to sustain embryo are developed (placenta, amniotic cavity and yolk sac)

At this stage Embryo is a flat germ disc comprising of 2 layers of cells 


At about day 15 - 2 layers separate and form a cavity

ECTODERM cells flow into the cavity to create the MESODERM

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Process starts on DAY 22, roughly halfway along NEURAL PLATE

cranial and caudal end open

Cranial Neuropore closes DAY 25  and Caudal Neuropore closes DAY 27

cells just above neural tube form the neural crest and migrate from neural tube

neurons and glia of the sensory and sympathetic ganglia

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Embryology of the spinal cord

develops from part of neural tube - caudal to 4th pair of somites - paired blocks of Mesoderm,segmentally arranged alongside neural groove

AFTER NEURALATION - lateral walls of tubes thicken and covered with Neuroplithelium

Cells form BASAL PLATE (anterior) and ALAR PLATE (posterior). separated by shallow groove - sulous lumitans

By week 10 - lumen of neural tube become a small central canal, Alar plate cells develop into ascending projection neurones and interneurones

involved in sensory pathways and reflex circuits

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Basal plate cells

differentiate into motor neurones and interneurones

cells in Thoracic segement develop into sympathetic Perganglionic neurones

Meninges around Spinal cord - develop from mesenchymal tissue surrounding neural tube - forms a membrane

Inner layer - Pia mater

Outer layer - dura mater

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Failure of caudal neuropore to close 

Disruption of Lumbal and Sacral segments of cord

Structures superficial to card also involved

Meringes, vertebral arch, paravertebral muscle skin

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Spina Bifida

Cleft spine - incomplete closure of spinal column - 3 Main types

SPINA BIFIFDA OCULTA - called oculta because its not obvious and involves only the bony part of the spine, nervous system develops normally, no symptoms. Only malformation is the incomplete closure of bone

SPINA BIFIDA MENINGOCELE - fairly common, covering of the spinal cord, defect of bone and soft tissue - sac filled with cerebrospinal fluid leads to bulge in the bulge.

Meninges - coverings of the brain and the spinal cord

Dura mater, the arachnoid mater + pia mater, moderate form of spina bifida, lumbar part of the spine spinal cord is not involved

SPINA BIFIDA MYELOMENIGOCELE - Herniation of the meninges and spinal cord through defect in the neural arches - Leads to spinal cord damage and paralysis, nerves roots are abnormally situated.

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