Lecture notes for Monday, March 7, 2016




subdivides by folding, to form 3 subdivisions: underlined below

Neural Tube Ectoderm: Which itself subdivides to form the following.


    Spinal cord

    Motor nerves (one segmental motor nerve per somite).

    Preganglionic Autonomic Nerves

    Neural Retina

    Pigmented Retina


Neural Crest Ectoderm:Which differentiates into many diverse cell types..

    Sensory nerves, dorsal root ganglia (one per somite)..

    Postganglionic autonomic nerves

    Melanocytes, and other mesenchymal pigment cells.

    Schwann Cells (but not oligodendrocytes).

    Facial Skeleton (Cell types that would be mesodermal in any other part of the body!).


Somatic Ectoderm: most of which becomes epidermis

    Some parts in the head become placodes

    A pair of olfactory placodes become nerves of nose

    A pair of lens placodes become the lenses of the eyes

    A pair of otic placodes become the inner ear (semi-circular canals, cochlea, etc.)

    In fish and amphibians, the lateral line system develops from placodes.

    The inner ear uses neuromast cells to detect sound, gravity & water flow; The lateral line system also uses neuromast cells to detect flow.










      Neuromast cells, right above here

Semi-Circular Canals in a living Xenopus tadpole



Otoliths in the same living Xenopus tadpole
These granules of calcium carbonate are embedded in a gel,
and detect which way is down, by pressure on neuromast cells.





Lens of a mammal eye:
Each cell is extremely long, extending from the posterior
side of the lens, almost all the way to the front





Eye cup with lens
























video: axons in culture




Retino-Tectal Projections were discussed on Friday, March 11. The remaining illustrations on this page have been moved to the new lecture notes for that date.







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