Embryology Biology 441 Spring 2009 Albert Harris
Which fact surprised you most so far?(The class will please vote about this.)
B) Mammal embryos have such a thick, strong jelly layer around them? (as you saw in a movie) C) Fusing with more than one sperm is fatal to further development? (called "P--------y") D) Oocytes have a resting voltage, like that of nerve and muscle cells? E) Potassium ions create a positive voltage outside cells, although their concentration is much higher inside? F) Fusion with the first sperm starts a wave of electrical depolarization, that spreads all over the egg cell's surface? G) This wave of depolarization has the same basic mechanism as nerve impulses? (although not as fast) H) This depolarization also allows calcium ions to enter (or sometimes be released) into the cytoplasm of the oocyte? I) The increased calcium concentration induces secretion of the contents of about 20,000 cortical granules, per oocyte (analogous to the secretion of synaptic vesicles by depolarized nerve axons). J) Which organ an embryonic cell will become part of is decided by cell location, i.e. where that cell is located at the blastula stage embryo, relative to the other cells. K) Decisions about which cells will become parts of which organs are (somehow!) decided in a branching pathway, in which the first three branches are...what? (called E-------, M------- and E-------) L) This subdivision of the embryo is done by an active geometrical rearrangement of cells? (This process of active cell rearrangement is called what? Starts with the letter G) M) Each of the three germ layers themselves get subdivided by other active geometric rearrangements? (For example, the cell rearrangement called n----------?, which subdivides what into what 3 parts.) N) All the differentiated cells of the body have a resting voltage, like nerves & muscles, & all will change their movements and shapes if a direct current voltage is imposed on them? O) When sea urchin larvae were first discovered (likewise starfish larvae, etc.) , they were thought to be adults of some new, unknown species of animals? P) Developing mammal embryos undergo rhythmic waves of active contraction, for many hours, at the age when they have about 30 to 80 cells! Q) Early cell divisions of mammal embryos occur with long time intervals between them (like ~20 hours) and are not synchronous (all cells don't divide at the same times). In contrast, in early embryos of sea urchins, fish, frogs, birds and flies, among many others, early divisions are very rapid (~every half hour, or even faster), and are synchronous (= simultaneous). Of these 17 facts, which ones had you not known before this semester?
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