Lecture notes for Friday, February 8
Ectodermsubdivides by folding, to form 3 subdivisions: underlined below
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 the 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.
Section through chick embryo pharyngeal region
Olfactory nerve and placodes in a living Xenopus tadpole
Otoliths in the same tadpole
Histological section through embryonic chick eye
Lens of a mammal eye:
Eye cup with lens
pigment cells in a tadpole
Stomodeum and Digestive Tract
The most anterior end of the digestive tract is formed by an infolding of the ectoderm called the stomodeum.
mouse tongue seen with polarized light
TeethThe outer layer of teeth (Ameloblasts --> Enamel)
dentin and enamel
section of a molar
The dark area is empty space, where the enamel had been but broke off
In case you were wondering, the Eustachian tube is named for Bartolomeo Eustachia, a sixteenth-century Italian anatomist 16th century Italian anatomist. This question came up in the lecture, but will not be asked on any exam.
Second Pharyngeal Pouch --> Tonsils
Third Pharyngeal Pouch --> Thymus and Parathyroid Gland
Fourth Pharyngeal Pouch --> Thymus and Parathyroid Gland
A question that might show up on an exam: what would happen if the third and fourth pharyngeal pouches did not develop properly?
Palatal shelves (which are only in mammals, not birds, not reptiles,
not amphibia or fish) separate the oral cavity from the nasal cavity, very much
like a pair of doors closing.
One of the 3 pairs of salivary glands and the anterior pituitary gland are stomodeal ectoderm. The rest of the digestive tract develops from endoderm, which will be covered in a later lecture.