Ectoderm

A collection of high-yield flashcards covering key terms and concepts in developmental biology.

Cleavage

Rapid mitotic divisions without growth between divisions; increases cell number only.

Karyokinesis

Division of the nucleus via mitotic spindle (microtubules).

Cytokinesis

Division of cytoplasm via actin contractile ring.

Holoblastic cleavage

Complete cleavage of the entire embryo (sparse yolk).

Meroblastic cleavage

Partial cleavage; yolk blocks full division.

Isolecithal egg

Uniform yolk distribution (e.g., sea urchin).

Telolecithal egg

Yolk concentrated in vegetal hemisphere (e.g., frog).

Centrolecithal egg

Yolk concentrated in center (e.g., fly).

Blastomere

Cell formed during cleavage.

Blastula

Hollow ball of cells formed after cleavage.

Blastocoel

Fluid-filled cavity inside blastula.

Blastopore

First opening of the developing GI tract.

Archenteron

Primitive gut formed during gastrulation.

Gastrulation

Coordinated cell movements forming the GI tract and three germ layers.

Invagination

Infolding of a sheet of cells that remains intact.

Ingression

Individual cells leave a sheet and migrate inward.

Epiboly

Expansion of epithelial sheet over embryo.

Delamination

Splitting of one cellular sheet into two parallel sheets.

Ectoderm

Outer germ layer; forms nervous system and epidermis.

Mesoderm

Middle germ layer; forms muscle, skeleton, connective tissue.

Endoderm

Inner germ layer; forms GI tract lining.

Neurulation

Rolling of ectoderm to form the neural tube.

Neural plate

Thickened ectoderm that forms neural tube.

Neural tube

Structure that becomes brain and spinal cord.

Neural crest

Migratory cells from neural tube border forming many structures.

Prosencephalon

Primary forebrain vesicle.

Mesencephalon

Primary midbrain vesicle.

Rhombencephalon

Primary hindbrain vesicle.

Telencephalon

Forms cerebral hemispheres.

Diencephalon

Forms thalamus, hypothalamus, optic vesicles.

Metencephalon

Forms cerebellum.

Myelencephalon

Forms medulla oblongata.

Dendrite

Receives neural input.

Axon

Sends neural output.

Synapse

Gap between neurons where signaling occurs.

Myelin sheath

Insulating layer around axon increasing signal speed.

Node of Ranvier

Gap in myelin enabling saltatory conduction.

Microtubules

Provide structure and axonal transport.

Microfilaments (Actin)

Responsible for cell movement and shape changes.

Monospermy

Entry of one sperm into egg.

Polyspermy

Entry of multiple sperm; lethal to embryo.