Neurulation
• occurs at or near the end of gastrulation and transforms the
gastrula into a neurula by establishing the central nervous
system
• the ectoderm gives rise to neural folds flanking a neural groove
along an axis from the blastopore toward the future head - these
sink into the dorsum of the embryo and the folds meet middorsally, forming a neural tube, of which the anterior part
becomes the brain and the rest, the spinal cord
• a population of mesodermal cells called chordamesoderm
aggregates to form the notochord - chordamesoderm generally
induces (embryonic induction) the neural tube to form (if the
chordamesoderm is removed experimentally, the neural tube
will not form)
During neurulation
• the chordamesoderm that will go to form the notochord
induces neural plate formation, which is the first stage in the
formation of the neural tube.
• characterized in most vertebrates by three stages
- during the neural plate stage, the ectoderm on the dorsal side
of the embryo overlying the notochord thickens to form the
neural plate
- at the neural fold stage, the thickened ectoderm folds,
leaving an elevated area along the neural groove. The neural
fold is wider in the anterior portion of the vertebrate embryo,
which is the region that will form the brain.
- during the neural tube stage, the neural folds move closer
together and fuse - the neural groove becomes the cavity within
the neural tube, which will later be capable of circulating
cerebrospinal fluid that aids in the function of the central
nervous system.
One derived characteristic found in vertebrates is the formation
of neural crest cells
• ectodermally derived
• develop along the top of the neural tube as the neural folds
close
• most neural crest cells change into mesenchyme, an embryonic
tissue that consists of star-shaped cells from all three germ
layers
• develop into the visceral skeleton (i.e. gill arches, some of
which will develop into jaws), pigment cells, sensory and
postganglionic neurons, the dentine-producing cells of teeth,
Schwann cells that help protect neurons, and bony scales