Gastrulation, Neurulation, and Somitogenesis – Key Vocabulary

A comprehensive set of vocabulary flashcards summarizing essential terms from the lecture on gastrulation, neurulation, neural crest, and somitogenesis.

Epithelial cells

Tightly connected, polarized embryonic cells that form sheets or tubes.

Mesenchymal cells

Loosely connected, migratory embryonic connective-tissue cells capable of independent movement.

Epithelial-to-mesenchymal transition (EMT)

Process by which epithelial cells lose polarity and adhesions, becoming invasive mesenchyme.

Mesenchymal-to-epithelial transition (MET)

Conversion of migratory mesenchymal cells back into polarized, tightly joined epithelial cells.

Gastrulation

Early embryonic process that forms the trilaminar disc (ectoderm, mesoderm, endoderm) via cell ingress through the primitive streak.

Primitive streak

Midline groove in epiblast whose formation marks the start of gastrulation and guides germ-layer formation.

Primitive (Hensen’s) node

Cranial end of the primitive streak that helps establish the embryo’s longitudinal axis and initiates notochord formation.

Trilaminar embryo

Embryo composed of three primary germ layers: ectoderm, mesoderm, and endoderm.

Endoderm

Innermost germ layer derived from epiblast cells that displace the hypoblast; forms gut lining and related organs.

Mesoderm

Middle germ layer formed by migrating epiblast cells; gives rise to muscle, bone, blood, and connective tissues.

Ectoderm

Outer germ layer consisting of remaining epiblast; produces epidermis and nervous system.

Notochord

Midline rod derived from notochordal process that induces neurulation and later becomes the nucleus pulposus.

Neurulation

Formation of the neural plate, folding into the neural tube, and closure of cranial and caudal neuropores.

Neural plate

Thickened ectoderm overlying the notochord that will fold to create the neural tube.

Neural groove

Midline depression between neural folds during neurulation.

Neural folds

Elevated lateral edges of the neural plate that converge and fuse to form the neural tube.

Neural tube

Closed structure formed from fused neural folds; precursor of brain and spinal cord.

Cranial (anterior) neuropore

Rostral opening of the neural tube that normally closes around day 25.

Caudal (posterior) neuropore

Caudal opening of the neural tube that normally closes around day 28.

Anencephaly

Congenital absence of major portions of the brain due to failure of cranial neuropore closure (days 23-25).

Encephalocele

Herniation of brain tissue through skull defect from incomplete cranial neuropore closure.

Spina bifida

Spectrum of defects resulting from failure of the caudal neuropore to close between days 22-28.

Neural crest cells

Cells arising from dorsal neural tube that migrate widely and generate diverse tissues.

Neural crest derivatives

Structures such as sensory and autonomic ganglia, Schwann cells, craniofacial bone, melanocytes, and adrenal medulla.

Situs inversus

Complete or partial mirror-image arrangement of organs, linked to abnormal left-right patterning during gastrulation.

Sirenomelia (Caudal dysgenesis)

Lower-body malformations (e.g., fused limbs) caused by insufficient caudal mesoderm production.

Sacrococcygeal teratoma

Tumor derived from persistent primitive streak cells containing multiple tissue types.

Embryonic folding

Transformation of flat germ-disc into cylindrical body through lateral and cephalocaudal folds.

Lateral folding

Rapid growth of parietal mesoderm and ectoderm that brings body walls ventrally to create body cavity.

Cephalocaudal folding

Ventral curvature caused by forebrain growth that positions heart and diaphragm into thorax.

Paraxial mesoderm

Mesoderm flanking the notochord that segments into somites.

Somitogenesis

Sequential formation of paired somites from paraxial mesoderm in a cranial-to-caudal wave.

Somite

Segmented block containing dermomyotome and sclerotome that gives rise to axial skeleton and skeletal muscle.

Dermatome

Somitic portion that forms dermis of back and trunk.

Myotome

Somitic cells that differentiate into skeletal muscle.

Sclerotome

Ventromedial somite derivative that forms vertebrae and ribs.

Lateral plate mesoderm

Peripheral mesoderm that splits into parietal (somatic) and visceral (splanchnic) layers.

Parietal (somatic) lateral plate

Dorsal layer forming limb bones, sternum, dermis of body wall, and parietal serous membranes.

Visceral (splanchnic) lateral plate

Ventral layer forming gut wall, cardiac muscle, visceral serous membranes, and connective tissue.

Somatopleure

Parietal lateral plate mesoderm plus overlying ectoderm; forms ventral body wall.

Splanchnopleure

Visceral lateral plate mesoderm plus endoderm; forms gut tube wall.

Lateral somitic frontier (LSF)

Boundary between somite and parietal lateral plate mesoderm crossed by migrating myogenic cells.

Abaxial domain

Muscle territory formed by myotome cells that cross the LSF into parietal lateral plate; becomes body-wall and limb muscles.

Primaxial domain

Muscles derived from myotome cells that remain medial to the LSF; includes intrinsic back and intercostal muscles.

Head mesoderm (Prechordal plate)

Anterior paraxial mesoderm that, with neural crest, forms skull and facial musculature without true somite segmentation.

Nucleus pulposus

Remnant of the notochord retained within intervertebral discs.