The central nervous system arises from the ectoderm as the neural plate. The neural plate folds to form a neural tube.
Day 18 (crown rump length CRL = 1.5mms)
The neural plate begins to thicken at the margins and the neural groove begins to form
The prosencephalon, mesencephalon and the rhomboencephalon, are differentiated by small neural folds.Day 21 (CRL = 3mms)
optic vesicles formed
The folding of the neural tube begins
At about day 25 after closure of the neural tube, sthere is subdivision and expansion of the neural tube with the prosencephalon mesencephalon and rhombencephalon becoming more distinct.
About 4th Week 3 primary Fluid Filled Vesicles
Day 26 (CRL = 3.00 mms)
The neural canal communicates with the amniotic fluid via the cranial and caudal openings or neuropores which close at about this time.
Rapid growth causes the neural tube to fold ventrally
Day 27 (CRL = 3.3mms)
closure of posterior neuropore
ventral horns appear
Brain and head represent 50% of total body length
Day 31 (CRL = 4.3mms )
At this stage during week 5 there is division of the prosencephalon and rhombencephalon, each, into two separate or secondary vesicles. The prosencephalon divides into an anterior telencephalon and a posterior diencephalon. The rhombencephalon divides into the metencephalon (future cerebellum and pons) and myelencephalon (future medulla).
The lateral ventricles form within the telencephalon, and the central lumen of the diencephalon will develop into the the third ventricle. The aqueduct of Sylvius is formed from within the mesencephalon and the fourth ventricle is frormed from within the rhomboencephalon.
It is during this time also, at about the fourth week that the primitive nervous system starts to fold. There are a few bends or flexures – The cranial flexure results in the prosencephalon flexing ventrally. The midbrain flexure is the most prominent flexure and develops along the ventral aspect of the mesencephalon.The cervical flexure develops at the junction of the myelencephalon and spinal cord.. There is also a pontine flexure between the midbrain and rhombencephalon.
5 Vesicles and Flexures Formed During Rapid Growth and Differentiation
Courtesy Ashley Davidoff MD Copyright 2010 98481b02b01.8s
Day 35 (CRL = 5.0mms)
5 cerebral vesicles are recognised
Prosencephalon (telencephalon diencephalon)
Rhombencephalon (metencephalon and myelencephalon)
In each of the 5 vesicles of the neural tube, the central lumen develops into the ventricular system .
Further Flexion and Bending With Rapid Growth
Courtesy Ashley Davidoff MD Copyright 2010 98481b03b05.8s
Day 42 (CRL = 13mms )
Day 56 (CRL = 25mms)
differentiation of cerebral cortex and meninges
Day 150 (CRL = 225mms)
primary cerebral fissures appear
Day 180 (CRL = 230mms)
Secondary cerebral sulci
Rapid brain growth
Head 25% of body length
The Final Product – Ready to Take on the World
Courtesy Ashley Davidoff MD Copyright 2010 98481b06b01.9s
Bionalogy.com – Excellent Graphics