Neural development

Question 1

Human morula formation

Answer 1

Morula (16-32 cells) forms by division from zygote

Contained within zone pellucida (no growth in size)

Question 2

Blastocyst/blastula formation

Answer 2

Inner cell mass cells are pluripotent embryonic cells (form embryo and nervous system)
Trophoblasts will form placenta
ICM cells form bilaminar disk. Epiblast cells near trophoblast cells (outer surface) and hypoblast cells near cavity

Question 3

Gastrulation

Answer 3

Forms primary germ layer
Epiblast cells from ICM converge at midline and ingress at primitive streak
Epiblast/hypoblast transformed to three primary germ layers
Ectoderm, mesoderm, endoderm

Question 4

Gastrulation in chick embryo

Answer 4

Hensen’s node is organiser for process of infolding
Order of cell arrival to blastocoel through node determines specification
Endoderm first, mesoderm, then ectoderm

Question 5

Germ layers

Answer 5

Ectoderm forms skin, nails, hair, nose and all parts of the nervous system
Mesoderm forms muscles, bones, lymphatic tissue
Endoderm forms lung lining, tongue, tonsils

Question 6

Gastrulation in human embryo

Answer 6

At day 5 blastocyst embeds into the endometrium (womb lining)
Day 14 primitive groove appears
Day 16 ingressing cells start to form early mesoderm

Question 7

Neuroectoderm formation

Answer 7

Subsection of ectoderm that gives rise to the nervous system
Cells move inwards from node (organiser)
Notochord is composed of cells derived from mesoderm. Defines axis of developing embryo
Part of ectoderm adjacent to notochord will form nervous system

Question 8

Transplantation in newts

Answer 8

Tissue taken from pigmented embryo and added to unpigmented embryo to determine which section induces gastrulation
Dorsal lip of blastopore

Question 9

Beta-catenin

Answer 9

Produced by Nieukwoop centre
Degraded by cells in vegetal pole but not animal pole (gradient)
Promotes action of beta-catenin in spemman’s organiser
Binds TCF3 to act as a TF. Activates genes (twin/siamois) that promote organiser protein synthesis
Wnt signalling stops beta-catenin degradation

Question 10

Neural inducer molecules

Answer 10

Diffusible signals from notochord causes neural differentiation in ectodermal cells (default fate)
BMP4 inhibits differentiation and leads to epidermal fate
Noggin, chordin and follistatin produced by notochord inhibit BMP4

Question 11

Neurulation

Answer 11

Neural plate induction
Neuroectodermal cells form neural plate (crest on each side)
Plate invaginates to form neural grove (crest along lips of groove)
Groove pinches off to form neural tube (neural crest combines)
Neural crest becomes PNS
Neural tube forms CNS

Question 12

Neural tube formation

Answer 12

Neural plate switches from E-cadherin to N-cadherin and N-CAM expression