Lecture notes for Monday, February 19
Ectoderm subdivides by folding, to form 3 subdivisions:
Neural Tube Ectoderm: Which itself subdivides to form the following.
Motor nerves (one segmental motor nerve per somite).
Preganglionic Autonomic Nerves
Neural Crest Ectoderm, which differentiates into many diverse cell types
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
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.